diff --git a/en_US.ISO8859-1/books/handbook/basics/chapter.xml b/en_US.ISO8859-1/books/handbook/basics/chapter.xml index d4500684b6..7642af7668 100644 --- a/en_US.ISO8859-1/books/handbook/basics/chapter.xml +++ b/en_US.ISO8859-1/books/handbook/basics/chapter.xml @@ -1,3717 +1,3752 @@ UNIX Basics Synopsis This chapter covers the basic commands and functionality of the &os; operating system. Much of this material is relevant for any &unix;-like operating system. New &os; users are encouraged to read through this chapter carefully. After reading this chapter, you will know: How to use and configure virtual consoles. How to create and manage users and groups on &os;. How &unix; file permissions and &os; file flags work. The default &os; file system layout. The &os; disk organization. How to mount and unmount file systems. What processes, daemons, and signals are. What a shell is, and how to change the default login environment. How to use basic text editors. What devices and device nodes are. How to read manual pages for more information. Virtual Consoles and Terminals virtual consoles terminals console Unless &os; has been configured to automatically start a graphical environment during startup, the system will boot into a command line login prompt, as seen in this example: FreeBSD/amd64 (pc3.example.org) (ttyv0) login: The first line contains some information about the system. The amd64 indicates that the system in this example is running a 64-bit version of &os;. The hostname is pc3.example.org, and ttyv0 indicates that this is the system console. The second line is the login prompt. Since &os; is a multiuser system, it needs some way to distinguish between different users. This is accomplished by requiring every user to log into the system before gaining access to the programs on the system. Every user has a unique name username and a personal password. To log into the system console, type the username that was configured during system installation, as described in , and press Enter. Then enter the password associated with the username and press Enter. The password is not echoed for security reasons. Once the correct password is input, the message of the day (MOTD) will be displayed followed by a command prompt. Depending upon the shell that was selected when the user was created, this prompt will be a #, $, or % character. The prompt indicates that the user is now logged into the &os; system console and ready to try the available commands. Virtual Consoles While the system console can be used to interact with the system, a user working from the command line at the keyboard of a &os; system will typically instead log into a virtual console. This is because system messages are configured by default to display on the system console. These messages will appear over the command or file that the user is working on, making it difficult to concentrate on the work at hand. By default, &os; is configured to provide several virtual consoles for inputting commands. Each virtual console has its own login prompt and shell and it is easy to switch between virtual consoles. This essentially provides the command line equivalent of having several windows open at the same time in a graphical environment. The key combinations AltF1 through AltF8 have been reserved by &os; for switching between virtual consoles. Use AltF1 to switch to the system console (ttyv0), AltF2 to access the first virtual console (ttyv1), AltF3 to access the second virtual console (ttyv2), and so on. When switching from one console to the next, &os; takes manages the screen output. The result is an illusion of having multiple virtual screens and keyboards that can be used to type commands for &os; to run. The programs that are launched in one virtual console do not stop running when the user switches to a different virtual console. Refer to &man.syscons.4;, &man.atkbd.4;, &man.vidcontrol.1; and &man.kbdcontrol.1; for a more technical description of the &os; console and its keyboard drivers. In &os;, the number of available virtual consoles is configured in this section of /etc/ttys: # name getty type status comments # ttyv0 "/usr/libexec/getty Pc" cons25 on secure # Virtual terminals ttyv1 "/usr/libexec/getty Pc" cons25 on secure ttyv2 "/usr/libexec/getty Pc" cons25 on secure ttyv3 "/usr/libexec/getty Pc" cons25 on secure ttyv4 "/usr/libexec/getty Pc" cons25 on secure ttyv5 "/usr/libexec/getty Pc" cons25 on secure ttyv6 "/usr/libexec/getty Pc" cons25 on secure ttyv7 "/usr/libexec/getty Pc" cons25 on secure ttyv8 "/usr/X11R6/bin/xdm -nodaemon" xterm off secure To disable a virtual console, put a comment symbol (#) at the beginning of the line representing that virtual console. For example, to reduce the number of available virtual consoles from eight to four, put a # in front of the last four lines representing virtual consoles ttyv5 through ttyv8. Do not comment out the line for the system console ttyv0. Note that the last virtual console (ttyv8) is used to access the graphical environment if &xorg; has been installed and configured as described in . For a detailed description of every column in this file and the available options for the virtual consoles, refer to &man.ttys.5;. Single User Mode The &os; boot menu provides an option labelled as Boot Single User. If this option is selected, the system will boot into a special mode known as single user mode. This mode is typically used to repair a system that will not boot or to reset the root password when it is not known. While in single user mode, networking and other virtual consoles are not available. However, full root access to the system is available, and by default, the root password is not needed. For these reasons, physical access to the keyboard is needed to boot into this mode and determining who has physical access to the keyboard is something to consider when securing a &os; system. The settings which control single user mode are found in this section of /etc/ttys: # name getty type status comments # # If console is marked "insecure", then init will ask for the root password # when going to single-user mode. console none unknown off secure By default, the status is set to secure. This assumes that who has physical access to the keyboard is either not important or it is controlled by a physical security policy. If this setting is changed to insecure, the assumption is that the environment itself is insecure because anyone can access the keyboard. When this line is changed to insecure, &os; will prompt for the root password when a user selects to boot into single user mode. Be careful when changing this setting to insecure! If the root password is forgotten, booting into single user mode is still possible, but may be difficult for someone who is not familiar with the &os; booting process. Changing Console Video Modes The &os; console default video mode may be adjusted to 1024x768, 1280x1024, or any other size supported by the graphics chip and monitor. To use a different video mode load the VESA module: &prompt.root; kldload vesa To determine which video modes are supported by the hardware, use &man.vidcontrol.1;. To get a list of supported video modes issue the following: &prompt.root; vidcontrol -i mode The output of this command lists the video modes that are supported by the hardware. To select a new video mode, specify the mode using &man.vidcontrol.1; as the root user: &prompt.root; vidcontrol MODE_279 If the new video mode is acceptable, it can be permanently set on boot by adding it to /etc/rc.conf: allscreens_flags="MODE_279" Users and Basic Account Management &os; allows multiple users to use the computer at the same time. While only one user can sit in front of the screen and use the keyboard at any one time, any number of users can log in to the system through the network. To use the system, each user should have their own user account. This chapter describes: The different types of user accounts on a &os; system. How to add, remove, and modify user accounts. How to set limits to control the resources that users and groups are allowed to access. How to create groups and add users as members of a group. Account Types Since all access to the &os; system is achieved using accounts and all processes are run by users, user and account management is important. There are three main types of accounts: system accounts, user accounts, and the superuser account. System Accounts accounts system System accounts are used to run services such as DNS, mail, and web servers. The reason for this is security; if all services ran as the superuser, they could act without restriction. accounts daemon accounts operator Examples of system accounts are daemon, operator, bind, news, and www. accounts nobody nobody is the generic unprivileged system account. However, the more services that use nobody, the more files and processes that user will become associated with, and hence the more privileged that user becomes. User Accounts accounts user User accounts are assigned to real people and are used to log in and use the system. Every person accessing the system should have a unique user account. This allows the administrator to find out who is doing what and prevents users from clobbering the settings of other users. Each user can set up their own environment to accommodate their use of the system, by configuring their default shell, editor, key bindings, and language settings. Every user account on a &os; system has certain information associated with it: User name The user name is typed at the login: prompt. Each user must have a unique user name. There are a number of rules for creating valid user names which are documented in &man.passwd.5;. It is recommended to use user names that consist of eight or fewer, all lower case characters in order to maintain backwards compatibility with applications. Password Each account has an associated password. User ID (UID) The User ID (UID) is a number used to uniquely identify the user to the &os; system. Commands that allow a user name to be specified will first convert it to the UID. It is recommended to use a UID less than 65535, since higher values may cause compatibility issues with some software. Group ID (GID) The Group ID (GID) is a number used to uniquely identify the primary group that the user belongs to. Groups are a mechanism for controlling access to resources based on a user's GID rather than their UID. This can significantly reduce the size of some configuration files and allows users to be members of more than one group. It is recommended to use a GID of 65535 or lower as higher GIDs may break some software. Login class Login classes are an extension to the group mechanism that provide additional flexibility when tailoring the system to different users. Login classes are discussed further in . Password change time By default, passwords do not expire. However, password expiration can be enabled on a per-user basis, forcing some or all users to change their passwords after a certain amount of time has elapsed. Account expiry time By default, &os; does not expire accounts. When creating accounts that need a limited lifespan, such as student accounts in a school, specify the account expiry date using &man.pw.8;. After the expiry time has elapsed, the account cannot be used to log in to the system, although the account's directories and files will remain. User's full name The user name uniquely identifies the account to &os;, but does not necessarily reflect the user's real name. Similar to a comment, this information can contain spaces, uppercase characters, and be more than 8 characters long. Home directory The home directory is the full path to a directory on the system. This is the user's starting directory when the user logs in. A common convention is to put all user home directories under /home/username or /usr/home/username. Each user stores their personal files and subdirectories in their own home directory. User shell The shell provides the user's default environment for interacting with the system. There are many different kinds of shells and experienced users will have their own preferences, which can be reflected in their account settings. The Superuser Account accounts superuser (root) The superuser account, usually called root, is used to manage the system with no limitations on privileges. For this reason, it should not be used for day-to-day tasks like sending and receiving mail, general exploration of the system, or programming. The superuser, unlike other user accounts, can operate without limits, and misuse of the superuser account may result in spectacular disasters. User accounts are unable to destroy the operating system by mistake, so it is recommended to login as a user account and to only become the superuser when a command requires extra privilege. Always double and triple-check any commands issued as the superuser, since an extra space or missing character can mean irreparable data loss. There are several ways to gain superuser privilege. While one can log in as root, this is highly discouraged. Instead, use &man.su.1; to become the superuser. If - is specified when running this command, the user will also inherit the root user's environment. The user running this command must be in the wheel group or else the command will fail. The user must also know the password for the root user account. In this example, the user only becomes superuser in order to run make install as this step requires superuser privilege. Once the command completes, the user types exit to leave the superuser account and return to the privilege of their user account. Install a Program As the Superuser &prompt.user; configure &prompt.user; make &prompt.user; su - Password: &prompt.root; make install &prompt.root; exit &prompt.user; The built-in &man.su.1; framework works well for single systems or small networks with just one system administrator. An alternative is to install the security/sudo package or port. This software provides activity logging and allows the administrator to configure which users can run which commands as the superuser. Managing Accounts accounts modifying &os; provides a variety of different commands to manage user accounts. The most common commands are summarized in , followed by some examples of their usage. See the manual page for each utility for more details and usage examples. Utilities for Managing User Accounts Command Summary &man.adduser.8; The recommended command-line application for adding new users. &man.rmuser.8; The recommended command-line application for removing users. &man.chpass.1; A flexible tool for changing user database information. &man.passwd.1; The command-line tool to change user passwords. &man.pw.8; A powerful and flexible tool for modifying all aspects of user accounts.
<command>adduser</command> accounts adding adduser /usr/share/skel skeleton directory The recommended program for adding new users is &man.adduser.8;. When a new user is added, this program automatically updates /etc/passwd and /etc/group. It also creates a home directory for the new user, copies in the default configuration files from /usr/share/skel, and can optionally mail the new user a welcome message. This utility must be run as the superuser. The &man.adduser.8; utility is interactive and walks through the steps for creating a new user account. As seen in , either input the required information or press Return to accept the default value shown in square brackets. In this example, the user has been invited into the wheel group, allowing them to become the superuser with &man.su.1;. When finished, the utility will prompt to either create another user or to exit. Adding a User on &os; &prompt.root; adduser Username: jru Full name: J. Random User Uid (Leave empty for default): Login group [jru]: Login group is jru. Invite jru into other groups? []: wheel Login class [default]: Shell (sh csh tcsh zsh nologin) [sh]: zsh Home directory [/home/jru]: Home directory permissions (Leave empty for default): Use password-based authentication? [yes]: Use an empty password? (yes/no) [no]: Use a random password? (yes/no) [no]: Enter password: Enter password again: Lock out the account after creation? [no]: Username : jru Password : **** Full Name : J. Random User Uid : 1001 Class : Groups : jru wheel Home : /home/jru Shell : /usr/local/bin/zsh Locked : no OK? (yes/no): yes adduser: INFO: Successfully added (jru) to the user database. Add another user? (yes/no): no Goodbye! &prompt.root; Since the password is not echoed when typed, be careful to not mistype the password when creating the user account. <command>rmuser</command> rmuser accounts removing To completely remove a user from the system, run &man.rmuser.8; as the superuser. This command performs the following steps: Removes the user's &man.crontab.1; entry, if one exists. Removes any &man.at.1; jobs belonging to the user. Kills all processes owned by the user. Removes the user from the system's local password file. Optionally removes the user's home directory, if it is owned by the user. Removes the incoming mail files belonging to the user from /var/mail. Removes all files owned by the user from temporary file storage areas such as /tmp. Finally, removes the username from all groups to which it belongs in /etc/group. If a group becomes empty and the group name is the same as the username, the group is removed. This complements the per-user unique groups created by &man.adduser.8;. &man.rmuser.8; cannot be used to remove superuser accounts since that is almost always an indication of massive destruction. By default, an interactive mode is used, as shown in the following example. <command>rmuser</command> Interactive Account Removal &prompt.root; rmuser jru Matching password entry: jru:*:1001:1001::0:0:J. Random User:/home/jru:/usr/local/bin/zsh Is this the entry you wish to remove? y Remove user's home directory (/home/jru)? y Removing user (jru): mailspool home passwd. &prompt.root; <command>chpass</command> chpass Any user can use &man.chpass.1; to change their default shell and personal information associated with their user account. The superuser can use this utility to change additional account information for any user. When passed no options, aside from an optional username, &man.chpass.1; displays an editor containing user information. When the user exits from the editor, the user database is updated with the new information. This utility will prompt for the user's password when exiting the editor, unless the utility is run as the superuser. In , the superuser has typed chpass jru and is now viewing the fields that can be changed for this user. If jru runs this command instead, only the last six fields will be displayed and available for editing. This is shown in . Using <command>chpass</command> as Superuser #Changing user database information for jru. Login: jru Password: * Uid [#]: 1001 Gid [# or name]: 1001 Change [month day year]: Expire [month day year]: Class: Home directory: /home/jru Shell: /usr/local/bin/zsh Full Name: J. Random User Office Location: Office Phone: Home Phone: Other information: Using <command>chpass</command> as Regular User #Changing user database information for jru. Shell: /usr/local/bin/zsh Full Name: J. Random User Office Location: Office Phone: Home Phone: Other information: The commands &man.chfn.1; and &man.chsh.1; are links to &man.chpass.1;, as are &man.ypchpass.1;, &man.ypchfn.1;, and &man.ypchsh.1;. Since NIS support is automatic, specifying the yp before the command is not necessary. How to configure NIS is covered in . <command>passwd</command> passwd accounts changing password Any user can easily change their password using &man.passwd.1;. To prevent accidental or unauthorized changes, this command will prompt for the user's original password before a new password can be set: Changing Your Password &prompt.user; passwd Changing local password for jru. Old password: New password: Retype new password: passwd: updating the database... passwd: done The superuser can change any user's password by specifying the username when running &man.passwd.1;. When this utility is run as the superuser, it will not prompt for the user's current password. This allows the password to be changed when a user cannot remember the original password. Changing Another User's Password as the Superuser &prompt.root; passwd jru Changing local password for jru. New password: Retype new password: passwd: updating the database... passwd: done As with &man.chpass.1;, &man.yppasswd.1; is a link to &man.passwd.1;, so NIS works with either command. <command>pw</command> pw The &man.pw.8; utility can create, remove, modify, and display users and groups. It functions as a front end to the system user and group files. &man.pw.8; has a very powerful set of command line options that make it suitable for use in shell scripts, but new users may find it more complicated than the other commands presented in this section. Limiting Users limiting users accounts limiting &os; provides several methods for an administrator to limit the amount of system resources an individual may use. These limits are discussed in two sections: disk quotas and other resource limits. quotas limiting users quotas disk quotas Disk quotas limit the amount of disk space available to users and provide a way to quickly check that usage without calculating it every time. Quotas are discussed in . The other resource limits include ways to limit the amount of CPU, memory, and other resources a user may consume. These are defined using login classes and are discussed here. /etc/login.conf Login classes are defined in /etc/login.conf and are described in detail in &man.login.conf.5;. Each user account is assigned to a login class, default by default, and each login class has a set of login capabilities associated with it. A login capability is a name=value pair, where name is a well-known identifier and value is an arbitrary string which is processed accordingly depending on the name. Setting up login classes and capabilities is rather straightforward and is also described in &man.login.conf.5;. &os; does not normally read the configuration in /etc/login.conf directly, but instead reads the /etc/login.conf.db database which provides faster lookups. Whenever /etc/login.conf is edited, the /etc/login.conf.db must be updated by executing the following command: &prompt.root; cap_mkdb /etc/login.conf Resource limits differ from the default login capabilities in two ways. First, for every limit, there is a soft (current) and hard limit. A soft limit may be adjusted by the user or application, but may not be set higher than the hard limit. The hard limit may be lowered by the user, but can only be raised by the superuser. Second, most resource limits apply per process to a specific user, not to the user as a whole. These differences are mandated by the specific handling of the limits, not by the implementation of the login capability framework. Below are the most commonly used resource limits. The rest of the limits, along with all the other login capabilities, can be found in &man.login.conf.5;. coredumpsize The limit on the size of a core file coredumpsize generated by a program is subordinate to other limits limiting users coredumpsize on disk usage, such as filesize, or disk quotas. This limit is often used as a less-severe method of controlling disk space consumption. Since users do not generate core files themselves, and often do not delete them, setting this may save them from running out of disk space should a large program crash. cputime The maximum amount of CPU cputime limiting users cputime time a user's process may consume. Offending processes will be killed by the kernel. This is a limit on CPU time consumed, not percentage of the CPU as displayed in some fields by &man.top.1; and &man.ps.1;. filesize The maximum size of a file filesize limiting users filesize the user may own. Unlike disk quotas, this limit is enforced on individual files, not the set of all files a user owns. maxproc The maximum number of processes maxproc limiting users maxproc a user can run. This includes foreground and background processes. This limit may not be larger than the system limit specified by the kern.maxproc &man.sysctl.8;. Setting this limit too small may hinder a user's productivity as it is often useful to be logged in multiple times or to execute pipelines. Some tasks, such as compiling a large program, start lots of processes. memorylocked The maximum amount of memory memorylocked limiting users memorylocked a process may request to be locked into main memory using &man.mlock.2;. Some system-critical programs, such as &man.amd.8;, lock into main memory so that if the system begins to swap, they do not contribute to disk thrashing. memoryuse The maximum amount of memory memoryuse limiting users memoryuse a process may consume at any given time. It includes both core memory and swap usage. This is not a catch-all limit for restricting memory consumption, but is a good start. openfiles The maximum number of files a process may have open openfiles limiting users openfiles . In &os;, files are used to represent sockets and IPC channels, so be careful not to set this too low. The system-wide limit for this is defined by the kern.maxfiles &man.sysctl.8;. sbsize The limit on the amount of network memory, and thus mbufs sbsize limiting users sbsize , a user may consume. This can be generally used to limit network communications. stacksize The maximum size of a process stack stacksize limiting users stacksize . This alone is not sufficient to limit the amount of memory a program may use so it should be used in conjunction with other limits. There are a few other things to remember when setting resource limits. Following are some general tips, suggestions, and miscellaneous comments. Processes started at system startup by /etc/rc are assigned to the daemon login class. Although the /etc/login.conf that comes with the system is a good source of reasonable values for most limits, they may not be appropriate for every system. Setting a limit too high may open the system up to abuse, while setting it too low may put a strain on productivity. Users of &xorg; should probably be granted more resources than other users. &xorg; by itself takes a lot of resources, but it also encourages users to run more programs simultaneously. Many limits apply to individual processes, not the user as a whole. For example, setting openfiles to 50 means that each process the user runs may open up to 50 files. The total amount of files a user may open is the value of openfiles multiplied by the value of maxproc. This also applies to memory consumption. For further information on resource limits and login classes and capabilities in general, refer to &man.cap.mkdb.1;, &man.getrlimit.2;, and &man.login.conf.5;. Managing Groups groups /etc/groups accounts groups A group is a list of users. A group is identified by its group name and GID. In &os;, the kernel uses the UID of a process, and the list of groups it belongs to, to determine what the process is allowed to do. Most of the time, the GID of a user or process usually means the first group in the list. The group name to GID mapping is listed in /etc/group. This is a plain text file with four colon-delimited fields. The first field is the group name, the second is the encrypted password, the third the GID, and the fourth the comma-delimited list of members. For a more complete description of the syntax, refer to &man.group.5;. The superuser can modify /etc/group using a text editor. Alternatively, &man.pw.8; can be used to add and edit groups. For example, to add a group called teamtwo and then confirm that it exists: Adding a Group Using &man.pw.8; &prompt.root; pw groupadd teamtwo &prompt.root; pw groupshow teamtwo teamtwo:*:1100: In this example, 1100 is the GID of teamtwo. Right now, teamtwo has no members. This command will add jru as a member of teamtwo. Adding User Accounts to a New Group Using &man.pw.8; &prompt.root; pw groupmod teamtwo -M jru &prompt.root; pw groupshow teamtwo teamtwo:*:1100:jru The argument to is a comma-delimited list of users to be added to a new (empty) group or to replace the members of an existing group. To the user, this group membership is different from (and in addition to) the user's primary group listed in the password file. This means that the user will not show up as a member when using with &man.pw.8;, but will show up when the information is queried via &man.id.1; or a similar tool. When &man.pw.8; is used to add a user to a group, it only manipulates /etc/group and does not attempt to read additional data from /etc/passwd. Adding a New Member to a Group Using &man.pw.8; &prompt.root; pw groupmod teamtwo -m db &prompt.root; pw groupshow teamtwo teamtwo:*:1100:jru,db In this example, the argument to is a comma-delimited list of users who are to be added to the group. Unlike the previous example, these users are appended to the group and do not replace existing users in the group. Using &man.id.1; to Determine Group Membership &prompt.user; id jru uid=1001(jru) gid=1001(jru) groups=1001(jru), 1100(teamtwo) In this example, jru is a member of the groups jru and teamtwo. For more information about this command and the format of /etc/group, refer to &man.pw.8; and &man.group.5;. Permissions UNIX In &os;, every file and directory has an associated set of permissions and several utilities are available for viewing and modifying these permissions. Understanding how permissions work is necessary to make sure that users are able to access the files that they need and are unable to improperly access the files used by the operating system or owned by other users. This section discusses the traditional &unix; permissions used in &os;. For finer grained file system access control, refer to . In &unix;, basic permissions are assigned using three types of access: read, write, and execute. These access types are used to determine file access to the file's owner, group, and others (everyone else). The read, write, and execute permissions can be represented as the letters r, w, and x. They can also be represented as binary numbers as each permission is either on or off (0). When represented as a number, the order is always read as rwx, where r has an on value of 4, w has an on value of 2 and x has an on value of 1. Table 4.1 summarizes the possible numeric and alphabetic possibilities. When reading the Directory Listing column, a - is used to represent a permission that is set to off. permissions file permissions &unix; Permissions Value Permission Directory Listing 0 No read, no write, no execute --- 1 No read, no write, execute --x 2 No read, write, no execute -w- 3 No read, write, execute -wx 4 Read, no write, no execute r-- 5 Read, no write, execute r-x 6 Read, write, no execute rw- 7 Read, write, execute rwx
&man.ls.1; directories Use the argument to &man.ls.1; to view a long directory listing that includes a column of information about a file's permissions for the owner, group, and everyone else. For example, a ls -l in an arbitrary directory may show: &prompt.user; ls -l total 530 -rw-r--r-- 1 root wheel 512 Sep 5 12:31 myfile -rw-r--r-- 1 root wheel 512 Sep 5 12:31 otherfile -rw-r--r-- 1 root wheel 7680 Sep 5 12:31 email.txt The first (leftmost) character in the first column indicates whether this file is a regular file, a directory, a special character device, a socket, or any other special pseudo-file device. In this example, the - indicates a regular file. The next three characters, rw- in this example, give the permissions for the owner of the file. The next three characters, r--, give the permissions for the group that the file belongs to. The final three characters, r--, give the permissions for the rest of the world. A dash means that the permission is turned off. In this example, the permissions are set so the owner can read and write to the file, the group can read the file, and the rest of the world can only read the file. According to the table above, the permissions for this file would be 644, where each digit represents the three parts of the file's permission. How does the system control permissions on devices? &os; treats most hardware devices as a file that programs can open, read, and write data to. These special device files are stored in /dev/. Directories are also treated as files. They have read, write, and execute permissions. The executable bit for a directory has a slightly different meaning than that of files. When a directory is marked executable, it means it is possible to change into that directory using &man.cd.1;. This also means that it is possible to access the files within that directory, subject to the permissions on the files themselves. In order to perform a directory listing, the read permission must be set on the directory. In order to delete a file that one knows the name of, it is necessary to have write and execute permissions to the directory containing the file. There are more permission bits, but they are primarily used in special circumstances such as setuid binaries and sticky directories. For more information on file permissions and how to set them, refer to &man.chmod.1;. Symbolic Permissions Tom Rhodes Contributed by permissions symbolic Symbolic permissions use characters instead of octal values to assign permissions to files or directories. Symbolic permissions use the syntax of (who) (action) (permissions), where the following values are available: Option Letter Represents (who) u User (who) g Group owner (who) o Other (who) a All (world) (action) + Adding permissions (action) - Removing permissions (action) = Explicitly set permissions (permissions) r Read (permissions) w Write (permissions) x Execute (permissions) t Sticky bit (permissions) s Set UID or GID These values are used with &man.chmod.1;, but with letters instead of numbers. For example, the following command would block other users from accessing FILE: &prompt.user; chmod go= FILE A comma separated list can be provided when more than one set of changes to a file must be made. For example, the following command removes the group and world write permission on FILE, and adds the execute permissions for everyone: &prompt.user; chmod go-w,a+x FILE &os; File Flags Tom Rhodes Contributed by In addition to file permissions, &os; supports the use of file flags. These flags add an additional level of security and control over files, but not directories. With file flags, even root can be prevented from removing or altering files. File flags are modified using &man.chflags.1;. For example, to enable the system undeletable flag on the file file1, issue the following command: &prompt.root; chflags sunlink file1 To disable the system undeletable flag, put a no in front of the : &prompt.root; chflags nosunlink file1 To view the flags of a file, use with &man.ls.1;: &prompt.root; ls -lo file1 -rw-r--r-- 1 trhodes trhodes sunlnk 0 Mar 1 05:54 file1 Several file flags may only be added or removed by the root user. In other cases, the file owner may set its file flags. Refer to &man.chflags.1; and &man.chflags.2; for more information. The <literal>setuid</literal>, <literal>setgid</literal>, and <literal>sticky</literal> Permissions Tom Rhodes Contributed by Other than the permissions already discussed, there are three other specific settings that all administrators should know about. They are the setuid, setgid, and sticky permissions. These settings are important for some &unix; operations as they provide functionality not normally granted to normal users. To understand them, the difference between the real user ID and effective user ID must be noted. The real user ID is the UID who owns or starts the process. The effective UID is the user ID the process runs as. As an example, &man.passwd.1; runs with the real user ID when a user changes their password. However, in order to update the password database, the command runs as the effective ID of the root user. This allows users to change their passwords without seeing a Permission Denied error. The setuid permission may be set by prefixing a permission set with the number four (4) as shown in the following example: &prompt.root; chmod 4755 suidexample.sh The permissions on suidexample.sh now look like the following: -rwsr-xr-x 1 trhodes trhodes 63 Aug 29 06:36 suidexample.sh Note that a s is now part of the permission set designated for the file owner, replacing the executable bit. This allows utilities which need elevated permissions, such as &man.passwd.1;. The nosuid &man.mount.8; option will cause such binaries to silently fail without alerting the user. That option is not completely reliable as a nosuid wrapper may be able to circumvent it. To view this in real time, open two terminals. On one, type passwd as a normal user. While it waits for a new password, check the process table and look at the user information for &man.passwd.1;: In terminal A: Changing local password for trhodes Old Password: In terminal B: &prompt.root; ps aux | grep passwd trhodes 5232 0.0 0.2 3420 1608 0 R+ 2:10AM 0:00.00 grep passwd root 5211 0.0 0.2 3620 1724 2 I+ 2:09AM 0:00.01 passwd Although &man.passwd.1; is run as a normal user, it is using the effective UID of root. The setgid permission performs the same function as the setuid permission; except that it alters the group settings. When an application or utility executes with this setting, it will be granted the permissions based on the group that owns the file, not the user who started the process. To set the setgid permission on a file, provide &man.chmod.1; with a leading two (2): &prompt.root; chmod 2755 sgidexample.sh In the following listing, notice that the s is now in the field designated for the group permission settings: -rwxr-sr-x 1 trhodes trhodes 44 Aug 31 01:49 sgidexample.sh In these examples, even though the shell script in question is an executable file, it will not run with a different EUID or effective user ID. This is because shell scripts may not access the &man.setuid.2; system calls. The setuid and setgid permission bits may lower system security, by allowing for elevated permissions. The third special permission, the sticky bit, can strengthen the security of a system. When the sticky bit is set on a directory, it allows file deletion only by the file owner. This is useful to prevent file deletion in public directories, such as /tmp, by users who do not own the file. To utilize this permission, prefix the permission set with a one (1): &prompt.root; chmod 1777 /tmp The sticky bit permission will display as a t at the very end of the permission set: &prompt.root; ls -al / | grep tmp drwxrwxrwt 10 root wheel 512 Aug 31 01:49 tmp Directory Structure directory hierarchy The &os; directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important directory is root or, /. This directory is the first one mounted at boot time and it contains the base system necessary to prepare the operating system for multi-user operation. The root directory also contains mount points for other file systems that are mounted during the transition to multi-user operation. A mount point is a directory where additional file systems can be grafted onto a parent file system (usually the root file system). This is further described in . Standard mount points include /usr/, /var/, /tmp/, /mnt/, and /cdrom/. These directories are usually referenced to entries in /etc/fstab. This file is a table of various file systems and mount points and is read by the system. Most of the file systems in /etc/fstab are mounted automatically at boot time from the script &man.rc.8; unless their entry includes . Details can be found in . A complete description of the file system hierarchy is available in &man.hier.7;. The following table provides a brief overview of the most common directories. Directory Description / Root directory of the file system. /bin/ User utilities fundamental to both single-user and multi-user environments. /boot/ Programs and configuration files used during operating system bootstrap. /boot/defaults/ Default boot configuration files. Refer to &man.loader.conf.5; for details. /dev/ Device nodes. Refer to &man.intro.4; for details. /etc/ System configuration files and scripts. /etc/defaults/ Default system configuration files. Refer to &man.rc.8; for details. /etc/mail/ Configuration files for mail transport agents such as &man.sendmail.8;. /etc/namedb/ &man.named.8; configuration files. /etc/periodic/ Scripts that run daily, weekly, and monthly, via &man.cron.8;. Refer to &man.periodic.8; for details. /etc/ppp/ &man.ppp.8; configuration files. /mnt/ Empty directory commonly used by system administrators as a temporary mount point. /proc/ Process file system. Refer to &man.procfs.5;, &man.mount.procfs.8; for details. /rescue/ Statically linked programs for emergency recovery as described in &man.rescue.8;. /root/ Home directory for the root account. /sbin/ System programs and administration utilities fundamental to both single-user and multi-user environments. /tmp/ Temporary files which are usually not preserved across a system reboot. A memory-based file system is often mounted at /tmp. This can be automated using the tmpmfs-related variables of &man.rc.conf.5; or with an entry in /etc/fstab; refer to &man.mdmfs.8; for details. /usr/ The majority of user utilities and applications. /usr/bin/ Common utilities, programming tools, and applications. /usr/include/ Standard C include files. /usr/lib/ Archive libraries. /usr/libdata/ Miscellaneous utility data files. /usr/libexec/ System daemons and system utilities executed by other programs. /usr/local/ Local executables and libraries. Also used as the default destination for the &os; ports framework. Within /usr/local, the general layout sketched out by &man.hier.7; for /usr should be used. Exceptions are the man directory, which is directly under /usr/local rather than under /usr/local/share, and the ports documentation is in share/doc/port. /usr/obj/ Architecture-specific target tree produced by building the /usr/src tree. /usr/ports/ The &os; Ports Collection (optional). /usr/sbin/ System daemons and system utilities executed by users. /usr/share/ Architecture-independent files. /usr/src/ BSD and/or local source files. /var/ Multi-purpose log, temporary, transient, and spool files. A memory-based file system is sometimes mounted at /var. This can be automated using the varmfs-related variables in &man.rc.conf.5; or with an entry in /etc/fstab; refer to &man.mdmfs.8; for details. /var/log/ Miscellaneous system log files. /var/mail/ User mailbox files. /var/spool/ Miscellaneous printer and mail system spooling directories. /var/tmp/ Temporary files which are usually preserved across a system reboot, unless /var is a memory-based file system. /var/yp/ NIS maps. Disk Organization The smallest unit of organization that &os; uses to find files is the filename. Filenames are case-sensitive, which means that readme.txt and README.TXT are two separate files. &os; does not use the extension of a file to determine whether the file is a program, document, or some other form of data. Files are stored in directories. A directory may contain no files, or it may contain many hundreds of files. A directory can also contain other directories, allowing a hierarchy of directories within one another in order to organize data. Files and directories are referenced by giving the file or directory name, followed by a forward slash, /, followed by any other directory names that are necessary. For example, if the directory foo contains a directory bar which contains the file readme.txt, the full name, or path, to the file is foo/bar/readme.txt. Note that this is different from &windows; which uses \ to separate file and directory names. &os; does not use drive letters, or other drive names in the path. For example, one would not type c:\foo\bar\readme.txt on &os;. Directories and files are stored in a file system. Each file system contains exactly one directory at the very top level, called the root directory for that file system. This root directory can contain other directories. One file system is designated the root file system or /. Every other file system is mounted under the root file system. No matter how many disks are on the &os; system, every directory appears to be part of the same disk. Consider three file systems, called A, B, and C. Each file system has one root directory, which contains two other directories, called A1, A2 (and likewise B1, B2 and C1, C2). Call A the root file system. If &man.ls.1; is used to view the contents of this directory, it will show two subdirectories, A1 and A2. The directory tree looks like this: / | +--- A1 | `--- A2 A file system must be mounted on to a directory in another file system. When mounting file system B on to the directory A1, the root directory of B replaces A1, and the directories in B appear accordingly: / | +--- A1 | | | +--- B1 | | | `--- B2 | `--- A2 Any files that are in the B1 or B2 directories can be reached with the path /A1/B1 or /A1/B2 as necessary. Any files that were in /A1 have been temporarily hidden. They will reappear if B is unmounted from A. If B had been mounted on A2 then the diagram would look like this: / | +--- A1 | `--- A2 | +--- B1 | `--- B2 and the paths would be /A2/B1 and /A2/B2 respectively. File systems can be mounted on top of one another. Continuing the last example, the C file system could be mounted on top of the B1 directory in the B file system, leading to this arrangement: / | +--- A1 | `--- A2 | +--- B1 | | | +--- C1 | | | `--- C2 | `--- B2 Or C could be mounted directly on to the A file system, under the A1 directory: / | +--- A1 | | | +--- C1 | | | `--- C2 | `--- A2 | +--- B1 | `--- B2 It is entirely possible to have one large root file system, and not need to create any others. There are some drawbacks to this approach, and one advantage. Benefits of Multiple File Systems Different file systems can have different mount options. For example, the root file system can be mounted read-only, making it impossible for users to inadvertently delete or edit a critical file. Separating user-writable file systems, such as /home, from other file systems allows them to be mounted nosuid. This option prevents the suid/guid bits on executables stored on the file system from taking effect, possibly improving security. &os; automatically optimizes the layout of files on a file system, depending on how the file system is being used. So a file system that contains many small files that are written frequently will have a different optimization to one that contains fewer, larger files. By having one big file system this optimization breaks down. &os;'s file systems are robust if power is lost. However, a power loss at a critical point could still damage the structure of the file system. By splitting data over multiple file systems it is more likely that the system will still come up, making it easier to restore from backup as necessary. Benefit of a Single File System File systems are a fixed size. If you create a file system when you install &os; and give it a specific size, you may later discover that you need to make the partition bigger. This is not easily accomplished without backing up, recreating the file system with the new size, and then restoring the backed up data. &os; features the &man.growfs.8; command, which makes it possible to increase the size of file system on the fly, removing this limitation. File systems are contained in partitions. This does not have the same meaning as the common usage of the term partition (for example, &ms-dos; partition), because of &os;'s &unix; heritage. Each partition is identified by a letter from a through to h. Each partition can contain only one file system, which means that file systems are often described by either their typical mount point in the file system hierarchy, or the letter of the partition they are contained in. &os; also uses disk space for swap space to provide virtual memory. This allows your computer to behave as though it has much more memory than it actually does. When &os; runs out of memory, it moves some of the data that is not currently being used to the swap space, and moves it back in (moving something else out) when it needs it. Some partitions have certain conventions associated with them. Partition Convention a Normally contains the root file system. b Normally contains swap space. c Normally the same size as the enclosing slice. This allows utilities that need to work on the entire slice, such as a bad block scanner, to work on the c partition. A file system would not normally be created on this partition. d Partition d used to have a special meaning associated with it, although that is now gone and d may work as any normal partition. Disks in &os; are divided into slices, referred to in &windows; as partitions, which are numbered from 1 to 4. These are then divided into partitions, which contain file systems, and are labeled using letters. slices partitions dangerously dedicated Slice numbers follow the device name, prefixed with an s, starting at 1. So da0s1 is the first slice on the first SCSI drive. There can only be four physical slices on a disk, but there can be logical slices inside physical slices of the appropriate type. These extended slices are numbered starting at 5, so ad0s5 is the first extended slice on the first IDE disk. These devices are used by file systems that expect to occupy a slice. Slices, dangerously dedicated physical drives, and other drives contain partitions, which are represented as letters from a to h. This letter is appended to the device name, so da0a is the a partition on the first da drive, which is dangerously dedicated. ad1s3e is the fifth partition in the third slice of the second IDE disk drive. Finally, each disk on the system is identified. A disk name starts with a code that indicates the type of disk, and then a number, indicating which disk it is. Unlike slices, disk numbering starts at 0. Common codes are listed in - . + . When referring to a partition, include the disk name, s, the slice number, and then the partition letter. Examples are shown in . shows a conceptual model of a disk layout. When installing &os;, configure the disk slices, create partitions within the slice to be used for &os;, create a file system or swap space in each partition, and decide where each file system will be mounted. - - Disk Device Codes +
+ Disk Device Names - Code - Meaning + Drive Type + Drive Device Name - ad - ATAPI (IDE) disk + IDE and SATA hard drives + ad or + ada - da - SCSI direct access disk + SCSI hard drives and + USB storage + devices + da - acd - ATAPI (IDE) CDROM + IDE and SATA CD-ROM + drives + acd or + cd - cd - SCSI CDROM + SCSI CD-ROM + drives + cd - fd - Floppy disk + Floppy drives + fd + + + + Assorted non-standard CD-ROM + drives + mcd for Mitsumi + CD-ROM and + scd for Sony + CD-ROM devices + + + + SCSI tape drives + sa + + + + IDE tape drives + ast + + + + RAID drives + Examples include aacd for &adaptec; AdvancedRAID, + mlxd and mlyd + for &mylex;, + amrd for AMI &megaraid;, + idad for Compaq Smart RAID, + twed for &tm.3ware; RAID.
Sample Disk, Slice, and Partition Names Name Meaning ad0s1a The first partition (a) on the first slice (s1) on the first IDE disk (ad0). da1s2e The fifth partition (e) on the second slice (s2) on the second SCSI disk (da1). Conceptual Model of a Disk This diagram shows &os;'s view of the first IDE disk attached to the system. Assume that the disk is 4 GB in size, and contains two 2 GB slices (&ms-dos; partitions). The first slice contains a &ms-dos; disk, C:, and the second slice contains a &os; installation. This example &os; installation has three data partitions, and a swap partition. The three partitions will each hold a file system. Partition a will be used for the root file system, e for the /var/ directory hierarchy, and f for the /usr/ directory hierarchy. .-----------------. --. | | | | DOS / Windows | | : : > First slice, ad0s1 : : | | | | :=================: ==: --. | | | Partition a, mounted as / | | | > referred to as ad0s2a | | | | | :-----------------: ==: | | | | Partition b, used as swap | | | > referred to as ad0s2b | | | | | :-----------------: ==: | Partition c, no | | | Partition e, used as /var > file system, all | | > referred to as ad0s2e | of FreeBSD slice, | | | | ad0s2c :-----------------: ==: | | | | | : : | Partition f, used as /usr | : : > referred to as ad0s2f | : : | | | | | | | | --' | `-----------------' --' Mounting and Unmounting File Systems The file system is best visualized as a tree, rooted, as it were, at /. /dev, /usr, and the other directories in the root directory are branches, which may have their own branches, such as /usr/local, and so on. root file system There are various reasons to house some of these directories on separate file systems. /var contains the directories log/, spool/, and various types of temporary files, and as such, may get filled up. Filling up the root file system is not a good idea, so splitting /var from / is often favorable. Another common reason to contain certain directory trees on other file systems is if they are to be housed on separate physical disks, or are separate virtual disks, such as Network File System mounts, described in , or CDROM drives. The <filename>fstab</filename> File file systems mounted with fstab During the boot process (), file systems listed in /etc/fstab are automatically mounted except for the entries containing . This file contains entries in the following format: device /mount-point fstype options dumpfreq passno device An existing device name as explained in . mount-point An existing directory on which to mount the file system. fstype The file system type to pass to &man.mount.8;. The default &os; file system is ufs. options Either for read-write file systems, or for read-only file systems, followed by any other options that may be needed. A common option is for file systems not normally mounted during the boot sequence. Other options are listed in &man.mount.8;. dumpfreq Used by &man.dump.8; to determine which file systems require dumping. If the field is missing, a value of zero is assumed. passno Determines the order in which file systems should be checked. File systems that should be skipped should have their passno set to zero. The root file system needs to be checked before everything else and should have its passno set to one. The other file systems should be set to values greater than one. If more than one file system has the same passno, &man.fsck.8; will attempt to check file systems in parallel if possible. Refer to &man.fstab.5; for more information on the format of /etc/fstab and its options. Using &man.mount.8; file systems mounting File systems are mounted using &man.mount.8;. The most basic syntax is as follows: &prompt.root; mount device mountpoint This command provides many options which are described in &man.mount.8;, The most commonly used options include: Mount Options Mount all the file systems listed in /etc/fstab, except those marked as noauto, excluded by the flag, or those that are already mounted. Do everything except for the actual mount system call. This option is useful in conjunction with the flag to determine what &man.mount.8; is actually trying to do. Force the mount of an unclean file system (dangerous), or the revocation of write access when downgrading a file system's mount status from read-write to read-only. Mount the file system read-only. This is identical to using . fstype Mount the specified file system type or mount only file systems of the given type, if is included. ufs is the default file system type. Update mount options on the file system. Be verbose. Mount the file system read-write. The following options can be passed to as a comma-separated list: nosuid Do not interpret setuid or setgid flags on the file system. This is also a useful security option. Using &man.umount.8; file systems unmounting To unmount a file system use &man.umount.8;. This command takes one parameter which can be a mountpoint, device name, or . All forms take to force unmounting, and for verbosity. Be warned that is not generally a good idea as it might crash the computer or damage data on the file system. To unmount all mounted file systems, or just the file system types listed after , use or . Note that does not attempt to unmount the root file system. Processes and Daemons &os; is a multi-tasking operating system. Each program running at any one time is called a process. Every running command starts at least one new process and there are a number of system processes that are run by &os;. Each process is uniquely identified by a number called a process ID (PID). Similar to files, each process has one owner and group, and the owner and group permissions are used to determine which files and devices the process can open. Most processes also have a parent process that started them. For example, the shell is a process, and any command started in the shell is a process which has the shell as its parent process. The exception is a special process called &man.init.8; which is always the first process to start at boot time and which always has a PID of 1. Some programs are not designed to be run with continuous user input and disconnect from the terminal at the first opportunity. For example, a web server responds to web requests, rather than user input. Mail servers are another example of this type of application. These types of programs are known as daemons. The term daemon comes from Greek mythology and represents an entity that is neither good nor evil, and which invisibly performs useful tasks. This is why the BSD mascot is the cheerful-looking daemon with sneakers and a pitchfork. There is a convention to name programs that normally run as daemons with a trailing d. For example, BIND is the Berkeley Internet Name Domain, but the actual program that executes is named. The Apache web server program is httpd and the line printer spooling daemon is lpd. This is only a naming convention. For example, the main mail daemon for the Sendmail application is sendmail, and not maild. Viewing Processes To see the processes running on the system, use &man.ps.1; or &man.top.1;. To display a static list of the currently running processes, their PIDs, how much memory they are using, and the command they were started with, use &man.ps.1;. To display all the running processes and update the display every few seconds in order to interactively see what the computer is doing, use &man.top.1;. By default, &man.ps.1; only shows the commands that are running and owned by the user. For example: &prompt.user; ps PID TT STAT TIME COMMAND 8203 0 Ss 0:00.59 /bin/csh 8895 0 R+ 0:00.00 ps The output from &man.ps.1; is organized into a number of columns. The PID column displays the process ID. PIDs are assigned starting at 1, go up to 99999, then wrap around back to the beginning. However, a PID is not reassigned if it is already in use. The TT column shows the tty the program is running on and STAT shows the program's state. TIME is the amount of time the program has been running on the CPU. This is usually not the elapsed time since the program was started, as most programs spend a lot of time waiting for things to happen before they need to spend time on the CPU. Finally, COMMAND is the command that was used to start the program. A number of different options are available to change the information that is displayed. One of the most useful sets is auxww, where displays information about all the running processes of all users, displays the username and memory usage of the process' owner, displays information about daemon processes, and causes &man.ps.1; to display the full command line for each process, rather than truncating it once it gets too long to fit on the screen. The output from &man.top.1; is similar: &prompt.user; top last pid: 9609; load averages: 0.56, 0.45, 0.36 up 0+00:20:03 10:21:46 107 processes: 2 running, 104 sleeping, 1 zombie CPU: 6.2% user, 0.1% nice, 8.2% system, 0.4% interrupt, 85.1% idle Mem: 541M Active, 450M Inact, 1333M Wired, 4064K Cache, 1498M Free ARC: 992M Total, 377M MFU, 589M MRU, 250K Anon, 5280K Header, 21M Other Swap: 2048M Total, 2048M Free PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND 557 root 1 -21 r31 136M 42296K select 0 2:20 9.96% Xorg 8198 dru 2 52 0 449M 82736K select 3 0:08 5.96% kdeinit4 8311 dru 27 30 0 1150M 187M uwait 1 1:37 0.98% firefox 431 root 1 20 0 14268K 1728K select 0 0:06 0.98% moused 9551 dru 1 21 0 16600K 2660K CPU3 3 0:01 0.98% top 2357 dru 4 37 0 718M 141M select 0 0:21 0.00% kdeinit4 8705 dru 4 35 0 480M 98M select 2 0:20 0.00% kdeinit4 8076 dru 6 20 0 552M 113M uwait 0 0:12 0.00% soffice.bin 2623 root 1 30 10 12088K 1636K select 3 0:09 0.00% powerd 2338 dru 1 20 0 440M 84532K select 1 0:06 0.00% kwin 1427 dru 5 22 0 605M 86412K select 1 0:05 0.00% kdeinit4 The output is split into two sections. The header (the first five or six lines) shows the PID of the last process to run, the system load averages (which are a measure of how busy the system is), the system uptime (time since the last reboot) and the current time. The other figures in the header relate to how many processes are running, how much memory and swap space has been used, and how much time the system is spending in different CPU states. If the ZFS file system module has been loaded, an ARC line indicates how much data was read from the memory cache instead of from disk. Below the header is a series of columns containing similar information to the output from &man.ps.1;, such as the PID, username, amount of CPU time, and the command that started the process. By default, &man.top.1; also displays the amount of memory space taken by the process. This is split into two columns: one for total size and one for resident size. Total size is how much memory the application has needed and the resident size is how much it is actually using now. &man.top.1; automatically updates the display every two seconds. A different interval can be specified with . Killing Processes One way to communicate with any running process or daemon is to send a signal using &man.kill.1;. There are a number of different signals; some have a specific meaning while others are described in the application's documentation. A user can only send a signal to a process they own and sending a signal to someone else's process will result in a permission denied error. The exception is the root user, who can send signals to anyone's processes. The operating system can also send a signal to a process. If an application is badly written and tries to access memory that it is not supposed to, &os; will send the process the Segmentation Violation signal (SIGSEGV). If an application has been written to use the &man.alarm.3; system call to be alerted after a period of time has elapsed, it will be sent the Alarm signal (SIGALRM). Two signals can be used to stop a process: SIGTERM and SIGKILL. SIGTERM is the polite way to kill a process as the process can read the signal, close any log files it may have open, and attempt to finish what it is doing before shutting down. In some cases, a process may ignore SIGTERM if it is in the middle of some task that can not be interrupted. SIGKILL can not be ignored by a process. Sending a SIGKILL to a process will usually stop that process there and then. There are a few tasks that can not be interrupted. For example, if the process is trying to read from a file that is on another computer on the network, and the other computer is unavailable, the process is said to be uninterruptible. Eventually the process will time out, typically after two minutes. As soon as this time out occurs the process will be killed.. Other commonly used signals are SIGHUP, SIGUSR1, and SIGUSR2. Since these are general purpose signals, different applications will respond differently. For example, after changing a web server's configuration file, the web server needs to be told to re-read its configuration. Restarting httpd would result in a brief outage period on the web server. Instead, send the daemon the SIGHUP signal. Be aware that different daemons will have different behavior, so refer to the documentation for the daemon to determine if SIGHUP will achieve the desired results. Sending a Signal to a Process This example shows how to send a signal to &man.inetd.8;. The &man.inetd.8; configuration file is /etc/inetd.conf, and &man.inetd.8; will re-read this configuration file when it is sent a SIGHUP. Find the PID of the process to send the signal to using &man.pgrep.1;. In this example, the PID for &man.inetd.8; is 198: &prompt.user; pgrep -l inetd 198 inetd -wW Use &man.kill.1; to send the signal. Because &man.inetd.8; is owned by root, use &man.su.1; to become root first. &prompt.user; su Password: &prompt.root; /bin/kill -s HUP 198 Like most &unix; commands, &man.kill.1; will not print any output if it is successful. If a signal is sent to a process not owned by that user, the message kill: PID: Operation not permitted will be displayed. Mistyping the PID will either send the signal to the wrong process, which could have negative results, or will send the signal to a PID that is not currently in use, resulting in the error kill: PID: No such process. Why Use <command>/bin/kill</command>? Many shells provide kill as a built in command, meaning that the shell will send the signal directly, rather than running /bin/kill. Be aware that different shells have a different syntax for specifying the name of the signal to send. Rather than try to learn all of them, it can be simpler to specify /bin/kill. When sending other signals, substitute TERM or KILL with the name of the signal. Killing a random process on the system is a bad idea. In particular, &man.init.8;, PID 1, is special. Running /bin/kill -s KILL 1 is a quick, and unrecommended, way to shutdown the system. Always double check the arguments to &man.kill.1; before pressing Return. Shells shells command line A shell provides a command line interface for interacting with the operating system. A shell receives commands from the input channel and executes them. Many shells provide built in functions to help with everyday tasks such as file management, file globbing, command line editing, command macros, and environment variables. &os; comes with several shells, including the Bourne shell (&man.sh.1;) and the extended C shell (&man.tcsh.1;). Other shells are available from the &os; Ports Collection, such as zsh and bash. The shell that is used is really a matter of taste. A C programmer might feel more comfortable with a C-like shell such as &man.tcsh.1;. A &linux; user might prefer bash. Each shell has unique properties that may or may not work with a user's preferred working environment, which is why there is a choice of which shell to use. One common shell feature is filename completion. After a user types the first few letters of a command or filename and presses Tab, the shell completes the rest of the command or filename. Consider two files called foobar and football. To delete foobar, the user might type rm foo and press Tab to complete the filename. But the shell only shows rm foo. It was unable to complete the filename because both foobar and football start with foo. Some shells sound a beep or show all the choices if more than one name matches. The user must then type more characters to identify the desired filename. Typing a t and pressing Tab again is enough to let the shell determine which filename is desired and fill in the rest. environment variables Another feature of the shell is the use of environment variables. Environment variables are a variable/key pair stored in the shell's environment. This environment can be read by any program invoked by the shell, and thus contains a lot of program configuration. provides a list of common environment variables and their meanings. Note that the names of environment variables are always in uppercase. Common Environment Variables Variable Description USER Current logged in user's name. PATH Colon-separated list of directories to search for binaries. DISPLAY Network name of the &xorg; display to connect to, if available. SHELL The current shell. TERM The name of the user's type of terminal. Used to determine the capabilities of the terminal. TERMCAP Database entry of the terminal escape codes to perform various terminal functions. OSTYPE Type of operating system. MACHTYPE The system's CPU architecture. EDITOR The user's preferred text editor. PAGER The user's preferred utility for viewing text one page at a time. MANPATH Colon-separated list of directories to search for manual pages.
Bourne shells How to set an environment variable differs between shells. In &man.tcsh.1; and &man.csh.1;, use setenv to set environment variables. In &man.sh.1; and bash, use export to set the current environment variables. This example sets the default EDITOR to /usr/local/bin/emacs for the &man.tcsh.1; shell: &prompt.user; setenv EDITOR /usr/local/bin/emacs The equivalent command for bash would be: &prompt.user; export EDITOR="/usr/local/bin/emacs" To expand an environment variable in order to see its current setting, type a $ character in front of its name on the command line. For example, echo $TERM displays the current $TERM setting. Shells treat special characters, known as meta-characters, as special representations of data. The most common meta-character is *, which represents any number of characters in a filename. Meta-characters can be used to perform filename globbing. For example, echo * is equivalent to ls because the shell takes all the files that match * and echo lists them on the command line. To prevent the shell from interpreting a special character, escape it from the shell by starting it with a backslash (\). For example, echo $TERM prints the terminal setting whereas echo \$TERM literally prints the string $TERM. Changing the Shell The easiest way to permanently change the default shell is to use chsh. Running this command will open the editor that is configured in the EDITOR environment variable, which by default is set to &man.vi.1;. Change the Shell: line to the full path of the new shell. Alternately, use chsh -s which will set the specified shell without opening an editor. For example, to change the shell to bash: &prompt.user; chsh -s /usr/local/bin/bash The new shell must be present in /etc/shells. If the shell was installed from the &os; Ports Collection as described in , it should be automatically added to this file. If it is missing, add it using this command, replacing the path with the path of the shell: &prompt.root; echo /usr/local/bin/bash >> /etc/shells Then, rerun &man.chsh.1;. Advanced Shell Techniques Tom Rhodes Written by The &unix; shell is not just a command interpreter, it acts as a powerful tool which allows users to execute commands, redirect their output, redirect their input and chain commands together to improve the final command output. When this functionality is mixed with built in commands, the user is provided with an environment that can maximize efficiency. Shell redirection is the action of sending the output or the input of a command into another command or into a file. To capture the output of the &man.ls.1; command, for example, into a file, simply redirect the output: &prompt.user; ls > directory_listing.txt The directory_listing.txt file will now contain the directory contents. Some commands allow you to read input in a similar one, such as &man.sort.1;. To sort this listing, redirect the input: &prompt.user; sort < directory_listing.txt The input will be sorted and placed on the screen. To redirect that input into another file, one could redirect the output of &man.sort.1; by mixing the direction: &prompt.user; sort < directory_listing.txt > sorted.txt In all of the previous examples, the commands are performing redirection using file descriptors. Every unix system has file descriptors; however, here we will focus on three, so named as Standard Input, Standard Output, and Standard Error. Each one has a purpose, where input could be a keyboard or a mouse, something that provides input. Output could be a screen or paper in a printer for example. And error would be anything that is used for diagnostic or error messages. All three are considered I/O based file descriptors and sometimes considered streams. Through the use of these descriptors, short named stdin, stdout, and stderr, the shell allows output and input to be passed around through various commands and redirected to or from a file. Another method of redirection is the pipe operator. The &unix; pipe operator, | allows the output of one command to be directly passed, or directed to another program. Basically a pipe will allow the standard output of a command to be passed as standard input to another command, for example: &prompt.user; cat directory_listing.txt | sort | less In that example, the contents of directory_listing.txt will be sorted and the output passed to &man.less.1;. This allows the user to scroll through the output at their own pace and prevent it from scrolling off the screen. Text Editors text editors editors Most &os; configuration is done by editing text files. Because of this, it is a good idea to become familiar with a text editor. &os; comes with a few as part of the base system, and many more are available in the Ports Collection. ee editors &man.ee.1; A simple editor to learn is &man.ee.1;, which stands for easy editor. To start this editor, type ee filename where filename is the name of the file to be edited. Once inside the editor, all of the commands for manipulating the editor's functions are listed at the top of the display. The caret (^) represents Ctrl, so ^e expands to Ctrl e . To leave &man.ee.1;, press Esc, then choose the leave editor option from the main menu. The editor will prompt to save any changes if the file has been modified. vi editors emacs &os; also comes with more powerful text editors, such as &man.vi.1;, as part of the base system. Other editors, like editors/emacs and editors/vim, are part of the &os; Ports Collection. These editors offer more functionality at the expense of being more complicated to learn. Learning a more powerful editor such as vim or Emacs can save more time in the long run. Many applications which modify files or require typed input will automatically open a text editor. To change the default editor, set the EDITOR environment variable as described in . Devices and Device Nodes A device is a term used mostly for hardware-related activities in a system, including disks, printers, graphics cards, and keyboards. When &os; boots, the majority of the boot messages refer to devices being detected. A copy of the boot messages are saved to /var/run/dmesg.boot. Each device has a device name and number. For example, acd0 is the first IDE CD-ROM drive, while kbd0 represents the keyboard. Most devices in a &os; must be accessed through special files called device nodes, which are located in /dev. Manual Pages manual pages The most comprehensive documentation on &os; is in the form of manual pages. Nearly every program on the system comes with a short reference manual explaining the basic operation and available arguments. These manuals can be viewed using man: &prompt.user; man command where command is the name of the command to learn about. For example, to learn more about &man.ls.1;, type: &prompt.user; man ls Manual pages are divided into sections which represent the type of topic. In &os;, the following sections are available: User commands. System calls and error numbers. Functions in the C libraries. Device drivers. File formats. Games and other diversions. Miscellaneous information. System maintenance and operation commands. System kernel interfaces. In some cases, the same topic may appear in more than one section of the online manual. For example, there is a chmod user command and a chmod() system call. To tell &man.man.1; which section to display, specify the section number: &prompt.user; man 1 chmod This will display the manual page for the user command &man.chmod.1;. References to a particular section of the online manual are traditionally placed in parenthesis in written documentation, so &man.chmod.1; refers to the user command and &man.chmod.2; refers to the system call. If the name of the manual page is unknown, use man -k to search for keywords in the manual page descriptions: &prompt.user; man -k mail This command displays a list of commands that have the keyword mail in their descriptions. This is equivalent to using &man.apropos.1;. To read the descriptions for the commands in /usr/bin, type: &prompt.user; cd /usr/bin &prompt.user; man -f * | more or &prompt.user; cd /usr/bin &prompt.user; whatis * |more GNU Info Files Free Software Foundation &os; includes many applications and utilities produced by the Free Software Foundation (FSF). In addition to manual pages, these programs may include hypertext documents called info files. These can be viewed using &man.info.1; or, if editors/emacs is installed, the info mode of emacs. To use &man.info.1;, type: &prompt.user; info For a brief introduction, type h. For a quick command reference, type ?. diff --git a/en_US.ISO8859-1/books/handbook/disks/chapter.xml b/en_US.ISO8859-1/books/handbook/disks/chapter.xml index d9b79c541c..54e52885ce 100644 --- a/en_US.ISO8859-1/books/handbook/disks/chapter.xml +++ b/en_US.ISO8859-1/books/handbook/disks/chapter.xml @@ -1,3685 +1,3579 @@ Storage Synopsis This chapter covers the use of disks and storage media in &os;. This includes SCSI and IDE disks, CD and DVD media, memory-backed disks, and USB storage devices. After reading this chapter, you will know: - - The terminology &os; uses to describe the organization - of data on a physical disk. - - How to add additional hard disks to a &os; system. How to grow the size of a disk's partition on &os;. How to configure &os; to use USB storage devices. How to use CD and DVD media on a &os; system. How to use the backup programs available under &os;. How to set up memory disks. What file system snapshots are and how to use them efficiently. How to use quotas to limit disk space usage. How to encrypt disks and swap to secure them against attackers. How to configure a highly available storage network. Before reading this chapter, you should: Know how to configure and install a new &os; kernel. - - Device Names - - The following is a list of physical storage devices - supported in &os; and their associated device names. - - - Physical Disk Naming Conventions - - - - - Drive type - Drive device name - - - - - - IDE hard drives - ad or - ada - - - - IDE CD-ROM - drives - acd or - cd - - - - SATA hard drives - ad or - ada - - - - SATA CD-ROM - drives - acd or - cd - - - - SCSI hard drives and - USB Mass storage - devices - da - - - - SCSI CD-ROM - drives - cd - - - - Assorted non-standard CD-ROM - drives - mcd for Mitsumi - CD-ROM and - scd for Sony - CD-ROM devices - - - - Floppy drives - fd - - - - SCSI tape drives - sa - - - - IDE tape drives - ast - - - - Flash drives - fla for &diskonchip; Flash - device - - - - RAID drives - aacd for &adaptec; AdvancedRAID, - mlxd and mlyd - for &mylex;, - amrd for AMI &megaraid;, - idad for Compaq Smart RAID, - twed for &tm.3ware; RAID. - - - -
- - Adding Disks David O'Brien Originally contributed by disks adding This section describes how to add a new SATA disk to a machine that currently only has a single drive. First, turn off the computer and install the drive in the computer following the instructions of the computer, controller, and drive manufacturers. Reboot the system and become root. Inspect /var/run/dmesg.boot to ensure the new disk was found. In this example, the newly added SATA drive will appear as ada1. partitions gpart For this example, a single large partition will be created on the new disk. The GPT partitioning scheme will be used in preference to the older and less versatile MBR scheme. If the disk to be added is not blank, old partition information can be removed with gpart delete. See &man.gpart.8; for details. The partition scheme is created, and then a single partition is added: &prompt.root; gpart create -s GPT ada1 &prompt.root; gpart add -t freebsd-ufs ada1 Depending on use, several smaller partitions may be desired. See &man.gpart.8; for options to create partitions smaller than a whole disk. A file system is created on the new blank disk: &prompt.root; newfs -U /dev/ada1p1 An empty directory is created as a mountpoint, a location for mounting the new disk in the original disk's file system: &prompt.root; mkdir /newdisk Finally, an entry is added to /etc/fstab so the new disk will be mounted automatically at startup: /dev/ada1p1 /newdisk ufs rw 2 2 The new disk can be mounted manually, without restarting the system: &prompt.root; mount /newdisk Resizing and Growing Disks Allan Jude Originally contributed by disks resizing A disk's capacity can increase without any changes to the data already present. This happens commonly with virtual machines, when the virtual disk turns out to be too small and is enlarged. Sometimes a disk image is written to a USB memory stick, but does not use the full capacity. Here we describe how to resize or grow disk contents to take advantage of increased capacity. Determine the device name of the disk to be resized by inspecting /var/run/dmesg.boot. In this example, there is only one SATA disk in the system, so the drive will appear as ada0. partitions gpart List the partitions on the disk to see the current configuration: &prompt.root; gpart show ada0 => 34 83886013 ada0 GPT (48G) [CORRUPT] 34 128 1 freebsd-boot (64k) 162 79691648 2 freebsd-ufs (38G) 79691810 4194236 3 freebsd-swap (2G) 83886046 1 - free - (512B) If the disk was formatted with the GPT partitioning scheme, it may show as corrupted because the GPT backup partition table is no longer at the end of the drive. Fix the backup partition table with gpart: &prompt.root; gpart recover ada0 ada0 recovered Now the additional space on the disk is available for use by a new partition, or an existing partition can be expanded: &prompt.root; gpart show ada0 => 34 102399933 ada0 GPT (48G) 34 128 1 freebsd-boot (64k) 162 79691648 2 freebsd-ufs (38G) 79691810 4194236 3 freebsd-swap (2G) 83886046 18513921 - free - (8.8G) Partitions can only be resized into contiguous free space. Here, the last partition on the disk is the swap partition, but the second partition is the one that needs to be resized. Swap partitions only contain temporary data, so it can safely be unmounted, deleted, and then recreated after resizing other partitions. &prompt.root; swapoff /dev/ada0p3 &prompt.root; gpart delete -i 3 ada0 ada0p3 deleted &prompt.root; gpart show ada0 => 34 102399933 ada0 GPT (48G) 34 128 1 freebsd-boot (64k) 162 79691648 2 freebsd-ufs (38G) 79691810 22708157 - free - (10G) There is risk of data loss when modifying the partition table of a mounted file system. It is best to perform the following steps on an unmounted file system while running from a live CD-ROM or USB device. However, if absolutely necessary, a mounted file system can be resized after disabling GEOM safety features: &prompt.root; sysctl kern.geom.debugflags=16 Resize the partition, leaving room to recreate a swap partition of the desired size. This only modifies the size of the partition. The file system in the partition will be expanded in a separate step. &prompt.root; gpart resize -i 2 -a 4k -s 47G ada0 ada0p2 resized &prompt.root; gpart show ada0 => 34 102399933 ada0 GPT (48G) 34 128 1 freebsd-boot (64k) 162 98566144 2 freebsd-ufs (47G) 98566306 3833661 - free - (1.8G) Recreate the swap partition: &prompt.root; gpart add -t freebsd-swap -a 4k ada0 ada0p3 added &prompt.root; gpart show ada0 => 34 102399933 ada0 GPT (48G) 34 128 1 freebsd-boot (64k) 162 98566144 2 freebsd-ufs (47G) 98566306 3833661 3 freebsd-swap (1.8G) &prompt.root; swapon /dev/ada0p3 Grow the UFS file system to use the new capacity of the resized partition: Growing a live UFS file system is only possible in &os; 10.0-RELEASE and later. For earlier versions, the file system must not be mounted. &prompt.root; growfs /dev/ada0p2 Device is mounted read-write; resizing will result in temporary write suspension for /. It's strongly recommended to make a backup before growing the file system. OK to grow file system on /dev/ada0p2, mounted on /, from 38GB to 47GB? [Yes/No] Yes super-block backups (for fsck -b #) at: 80781312, 82063552, 83345792, 84628032, 85910272, 87192512, 88474752, 89756992, 91039232, 92321472, 93603712, 94885952, 96168192, 97450432 Both the partition and the file system on it have now been resized to use the newly-available disk space. <acronym>USB</acronym> Storage Devices Marc Fonvieille Contributed by USB disks Many external storage solutions, such as hard drives, USB thumbdrives, and CD and DVD burners, use the Universal Serial Bus (USB). &os; provides support for USB 1.x, 2.0, and 3.0 devices. USB 3.0 support is not compatible with some hardware, including Haswell (Lynx point) chipsets. If &os; boots with a failed with error 19 message, disable xHCI/USB3 in the system BIOS. Support for USB storage devices is built into the GENERIC kernel. For a custom kernel, be sure that the following lines are present in the kernel configuration file: device scbus # SCSI bus (required for ATA/SCSI) device da # Direct Access (disks) device pass # Passthrough device (direct ATA/SCSI access) device uhci # provides USB 1.x support device ohci # provides USB 1.x support device ehci # provides USB 2.0 support device xhci # provides USB 3.0 support device usb # USB Bus (required) device umass # Disks/Mass storage - Requires scbus and da device cd # needed for CD and DVD burners &os; uses the &man.umass.4; driver which uses the SCSI subsystem to access USB storage devices. Since any USB device will be seen as a SCSI device by the system, if the USB device is a CD or DVD burner, do not include in a custom kernel configuration file. The rest of this section demonstrates how to verify that a USB storage device is recognized by &os; and how to configure the device so that it can be used. Device Configuration To test the USB configuration, plug in the USB device. Use dmesg to confirm that the drive appears in the system message buffer. It should look something like this: umass0: <STECH Simple Drive, class 0/0, rev 2.00/1.04, addr 3> on usbus0 umass0: SCSI over Bulk-Only; quirks = 0x0100 umass0:4:0:-1: Attached to scbus4 da0 at umass-sim0 bus 0 scbus4 target 0 lun 0 da0: <STECH Simple Drive 1.04> Fixed Direct Access SCSI-4 device da0: Serial Number WD-WXE508CAN263 da0: 40.000MB/s transfers da0: 152627MB (312581808 512 byte sectors: 255H 63S/T 19457C) da0: quirks=0x2<NO_6_BYTE> The brand, device node (da0), speed, and size will differ according to the device. Since the USB device is seen as a SCSI one, camcontrol can be used to list the USB storage devices attached to the system: &prompt.root; camcontrol devlist <STECH Simple Drive 1.04> at scbus4 target 0 lun 0 (pass3,da0) Alternately, usbconfig can be used to list the device. Refer to &man.usbconfig.8; for more information about this command. &prompt.root; usbconfig ugen0.3: <Simple Drive STECH> at usbus0, cfg=0 md=HOST spd=HIGH (480Mbps) pwr=ON (2mA) If the device has not been formatted, refer to for instructions on how to format and create partitions on the USB drive. If the drive comes with a file system, it can be mounted by root using the instructions in . Allowing untrusted users to mount arbitrary media, by enabling vfs.usermount as described below, should not be considered safe from a security point of view. Most file systems were not built to safeguard against malicious devices. To make the device mountable as a normal user, one solution is to make all users of the device a member of the operator group using &man.pw.8;. Next, ensure that operator is able to read and write the device by adding these lines to /etc/devfs.rules: [localrules=5] add path 'da*' mode 0660 group operator If internal SCSI disks are also installed in the system, change the second line as follows: add path 'da[3-9]*' mode 0660 group operator This will exclude the first three SCSI disks (da0 to da2)from belonging to the operator group. Replace 3 with the number of internal SCSI disks. Refer to &man.devfs.rules.5; for more information about this file. Next, enable the ruleset in /etc/rc.conf: devfs_system_ruleset="localrules" Then, instruct the system to allow regular users to mount file systems by adding the following line to /etc/sysctl.conf: vfs.usermount=1 Since this only takes effect after the next reboot, use sysctl to set this variable now: &prompt.root; sysctl vfs.usermount=1 vfs.usermount: 0 -> 1 The final step is to create a directory where the file system is to be mounted. This directory needs to be owned by the user that is to mount the file system. One way to do that is for root to create a subdirectory owned by that user as /mnt/username. In the following example, replace username with the login name of the user and usergroup with the user's primary group: &prompt.root; mkdir /mnt/username &prompt.root; chown username:usergroup /mnt/username Suppose a USB thumbdrive is plugged in, and a device /dev/da0s1 appears. If the device is formatted with a FAT file system, the user can mount it using: &prompt.user; mount -t msdosfs -o -m=644,-M=755 /dev/da0s1 /mnt/username Before the device can be unplugged, it must be unmounted first: &prompt.user; umount /mnt/username After device removal, the system message buffer will show messages similar to the following: umass0: at uhub3, port 2, addr 3 (disconnected) da0 at umass-sim0 bus 0 scbus4 target 0 lun 0 da0: <STECH Simple Drive 1.04> s/n WD-WXE508CAN263 detached (da0:umass-sim0:0:0:0): Periph destroyed Creating and Using <acronym>CD</acronym> Media Mike Meyer Contributed by CD-ROMs creating Compact Disc (CD) media provide a number of features that differentiate them from conventional disks. They are designed so that they can be read continuously without delays to move the head between tracks. While CD media do have tracks, these refer to a section of data to be read continuously, and not a physical property of the disk. The ISO 9660 file system was designed to deal with these differences. ISO 9660 file systems ISO 9660 CD burner ATAPI The &os; Ports Collection provides several utilities for burning and duplicating audio and data CDs. This chapter demonstrates the use of several command line utilities. For CD burning software with a graphical utility, consider installing the sysutils/xcdroast or sysutils/k3b packages or ports. Supported Devices Marc Fonvieille Contributed by CD burner ATAPI/CAM driver The GENERIC kernel provides support for SCSI, USB, and ATAPI CD readers and burners. If a custom kernel is used, the options that need to be present in the kernel configuration file vary by the type of device. For a SCSI burner, make sure these options are present: device scbus # SCSI bus (required for ATA/SCSI) device da # Direct Access (disks) device pass # Passthrough device (direct ATA/SCSI access) device cd # needed for CD and DVD burners For a USB burner, make sure these options are present: device scbus # SCSI bus (required for ATA/SCSI) device da # Direct Access (disks) device pass # Passthrough device (direct ATA/SCSI access) device cd # needed for CD and DVD burners device uhci # provides USB 1.x support device ohci # provides USB 1.x support device ehci # provides USB 2.0 support device xhci # provides USB 3.0 support device usb # USB Bus (required) device umass # Disks/Mass storage - Requires scbus and da For an ATAPI burner, make sure these options are present: device ata # Legacy ATA/SATA controllers device scbus # SCSI bus (required for ATA/SCSI) device pass # Passthrough device (direct ATA/SCSI access) device cd # needed for CD and DVD burners On &os; versions prior to 10.x, this line is also needed in the kernel configuration file if the burner is an ATAPI device: device atapicam Alternately, this driver can be loaded at boot time by adding the following line to /boot/loader.conf: atapicam_load="YES" This will require a reboot of the system as this driver can only be loaded at boot time. To verify that &os; recognizes the device, run dmesg and look for an entry for the device. On systems prior to 10.x, the device name in the first line of the output will be acd0 instead of cd0. &prompt.user; dmesg | grep cd cd0 at ahcich1 bus 0 scbus1 target 0 lun 0 cd0: <HL-DT-ST DVDRAM GU70N LT20> Removable CD-ROM SCSI-0 device cd0: Serial Number M3OD3S34152 cd0: 150.000MB/s transfers (SATA 1.x, UDMA6, ATAPI 12bytes, PIO 8192bytes) cd0: Attempt to query device size failed: NOT READY, Medium not present - tray closed Burning a <acronym>CD</acronym> In &os;, cdrecord can be used to burn CDs. This command is installed with the sysutils/cdrtools package or port. &os; 8.x includes the built-in burncd utility for burning CDs using an ATAPI CD burner. Refer to the manual page for burncd for usage examples. While cdrecord has many options, basic usage is simple. Specify the name of the ISO file to burn and, if the system has multiple burner devices, specify the name of the device to use: &prompt.root; cdrecord dev=device imagefile.iso To determine the device name of the burner, use which might produce results like this: CD-ROMs burning &prompt.root; cdrecord -scanbus ProDVD-ProBD-Clone 3.00 (amd64-unknown-freebsd10.0) Copyright (C) 1995-2010 Jörg Schilling Using libscg version 'schily-0.9' scsibus0: 0,0,0 0) 'SEAGATE ' 'ST39236LW ' '0004' Disk 0,1,0 1) 'SEAGATE ' 'ST39173W ' '5958' Disk 0,2,0 2) * 0,3,0 3) 'iomega ' 'jaz 1GB ' 'J.86' Removable Disk 0,4,0 4) 'NEC ' 'CD-ROM DRIVE:466' '1.26' Removable CD-ROM 0,5,0 5) * 0,6,0 6) * 0,7,0 7) * scsibus1: 1,0,0 100) * 1,1,0 101) * 1,2,0 102) * 1,3,0 103) * 1,4,0 104) * 1,5,0 105) 'YAMAHA ' 'CRW4260 ' '1.0q' Removable CD-ROM 1,6,0 106) 'ARTEC ' 'AM12S ' '1.06' Scanner 1,7,0 107) * Locate the entry for the CD burner and use the three numbers separated by commas as the value for . In this case, the Yamaha burner device is 1,5,0, so the appropriate input to specify that device is . Refer to the manual page for cdrecord for other ways to specify this value and for information on writing audio tracks and controlling the write speed. Alternately, run the following command to get the device address of the burner: &prompt.root; camcontrol devlist <MATSHITA CDRW/DVD UJDA740 1.00> at scbus1 target 0 lun 0 (cd0,pass0) Use the numeric values for scbus, target, and lun. For this example, 1,0,0 is the device name to use. Writing Data to an <acronym>ISO</acronym> File System In order to produce a data CD, the data files that are going to make up the tracks on the CD must be prepared before they can be burned to the CD. In &os;, sysutils/cdrtools installs mkisofs, which can be used to produce an ISO 9660 file system that is an image of a directory tree within a &unix; file system. The simplest usage is to specify the name of the ISO file to create and the path to the files to place into the ISO 9660 file system: &prompt.root; mkisofs -o imagefile.iso /path/to/tree file systems ISO 9660 This command maps the file names in the specified path to names that fit the limitations of the standard ISO 9660 file system, and will exclude files that do not meet the standard for ISO file systems. file systems Joliet A number of options are available to overcome the restrictions imposed by the standard. In particular, enables the Rock Ridge extensions common to &unix; systems and enables Joliet extensions used by µsoft; systems. For CDs that are going to be used only on &os; systems, can be used to disable all filename restrictions. When used with , it produces a file system image that is identical to the specified &os; tree, even if it violates the ISO 9660 standard. CD-ROMs creating bootable The last option of general use is . This is used to specify the location of a boot image for use in producing an El Torito bootable CD. This option takes an argument which is the path to a boot image from the top of the tree being written to the CD. By default, mkisofs creates an ISO image in floppy disk emulation mode, and thus expects the boot image to be exactly 1200, 1440 or 2880 KB in size. Some boot loaders, like the one used by the &os; distribution media, do not use emulation mode. In this case, should be used. So, if /tmp/myboot holds a bootable &os; system with the boot image in /tmp/myboot/boot/cdboot, this command would produce /tmp/bootable.iso: &prompt.root; mkisofs -R -no-emul-boot -b boot/cdboot -o /tmp/bootable.iso /tmp/myboot The resulting ISO image can be mounted as a memory disk with: &prompt.root; mdconfig -a -t vnode -f /tmp/bootable.iso -u 0 &prompt.root; mount -t cd9660 /dev/md0 /mnt One can then verify that /mnt and /tmp/myboot are identical. There are many other options available for mkisofs to fine-tune its behavior. Refer to &man.mkisofs.8; for details. It is possible to copy a data CD to an image file that is functionally equivalent to the image file created with mkisofs. To do so, use dd with the device name as the input file and the name of the ISO to create as the output file: &prompt.root; dd if=/dev/cd0 of=file.iso bs=2048 The resulting image file can be burned to CD as described in . Using Data <acronym>CD</acronym>s Once an ISO has been burned to a CD, it can be mounted by specifying the file system type, the name of the device containing the CD, and an existing mount point: &prompt.root; mount -t cd9660 /dev/cd0 /mnt Since mount assumes that a file system is of type ufs, a Incorrect super block error will occur if -t cd9660 is not included when mounting a data CD. While any data CD can be mounted this way, disks with certain ISO 9660 extensions might behave oddly. For example, Joliet disks store all filenames in two-byte Unicode characters. If some non-English characters show up as question marks, specify the local charset with . For more information, refer to &man.mount.cd9660.8;. In order to do this character conversion with the help of , the kernel requires the cd9660_iconv.ko module to be loaded. This can be done either by adding this line to loader.conf: cd9660_iconv_load="YES" and then rebooting the machine, or by directly loading the module with kldload. Occasionally, Device not configured will be displayed when trying to mount a data CD. This usually means that the CD drive thinks that there is no disk in the tray, or that the drive is not visible on the bus. It can take a couple of seconds for a CD drive to realize that a media is present, so be patient. Sometimes, a SCSI CD drive may be missed because it did not have enough time to answer the bus reset. To resolve this, a custom kernel can be created which increases the default SCSI delay. Add the following option to the custom kernel configuration file and rebuild the kernel using the instructions in : options SCSI_DELAY=15000 This tells the SCSI bus to pause 15 seconds during boot, to give the CD drive every possible chance to answer the bus reset. It is possible to burn a file directly to CD, without creating an ISO 9660 file system. This is known as burning a raw data CD and some people do this for backup purposes. This type of disk can not be mounted as a normal data CD. In order to retrieve the data burned to such a CD, the data must be read from the raw device node. For example, this command will extract a compressed tar file located on the second CD device into the current working directory: &prompt.root; tar xzvf /dev/cd1 In order to mount a data CD, the data must be written using mkisofs. Duplicating Audio <acronym>CD</acronym>s To duplicate an audio CD, extract the audio data from the CD to a series of files, then write these files to a blank CD. describes how to duplicate and burn an audio CD. If the &os; version is less than 10.0 and the device is ATAPI, the module must be first loaded using the instructions in . Duplicating an Audio <acronym>CD</acronym> The sysutils/cdrecord package or port installs cdda2wav. This command can be used to extract all of the audio tracks, with each track written to a separate WAV file in the current working directory: &prompt.user; cdda2wav -vall -B -Owav A device name does not need to be specified if there is only one CD device on the system. Refer to the cdda2wav manual page for instructions on how to specify a device and to learn more about the other options available for this command. Use cdrecord to write the .wav files: &prompt.user; cdrecord -v dev=2,0 -dao -useinfo *.wav Make sure that 2,0 is set appropriately, as described in . Creating and Using <acronym>DVD</acronym> Media Marc Fonvieille Contributed by Andy Polyakov With inputs from DVD burning Compared to the CD, the DVD is the next generation of optical media storage technology. The DVD can hold more data than any CD and is the standard for video publishing. Five physical recordable formats can be defined for a recordable DVD: DVD-R: This was the first DVD recordable format available. The DVD-R standard is defined by the DVD Forum. This format is write once. DVD-RW: This is the rewritable version of the DVD-R standard. A DVD-RW can be rewritten about 1000 times. DVD-RAM: This is a rewritable format which can be seen as a removable hard drive. However, this media is not compatible with most DVD-ROM drives and DVD-Video players as only a few DVD writers support the DVD-RAM format. Refer to for more information on DVD-RAM use. DVD+RW: This is a rewritable format defined by the DVD+RW Alliance. A DVD+RW can be rewritten about 1000 times. DVD+R: This format is the write once variation of the DVD+RW format. A single layer recordable DVD can hold up to 4,700,000,000 bytes which is actually 4.38 GB or 4485 MB as 1 kilobyte is 1024 bytes. A distinction must be made between the physical media and the application. For example, a DVD-Video is a specific file layout that can be written on any recordable DVD physical media such as DVD-R, DVD+R, or DVD-RW. Before choosing the type of media, ensure that both the burner and the DVD-Video player are compatible with the media under consideration. Configuration To perform DVD recording, use &man.growisofs.1;. This command is part of the sysutils/dvd+rw-tools utilities which support all DVD media types. These tools use the SCSI subsystem to access the devices, therefore ATAPI/CAM support must be loaded or statically compiled into the kernel. This support is not needed if the burner uses the USB interface. Refer to for more details on USB device configuration. DMA access must also be enabled for ATAPI devices, by adding the following line to /boot/loader.conf: hw.ata.atapi_dma="1" Before attempting to use dvd+rw-tools, consult the Hardware Compatibility Notes. For a graphical user interface, consider using sysutils/k3b which provides a user friendly interface to &man.growisofs.1; and many other burning tools. Burning Data <acronym>DVD</acronym>s Since &man.growisofs.1; is a front-end to mkisofs, it will invoke &man.mkisofs.8; to create the file system layout and perform the write on the DVD. This means that an image of the data does not need to be created before the burning process. To burn to a DVD+R or a DVD-R the data in /path/to/data, use the following command: &prompt.root; growisofs -dvd-compat -Z /dev/cd0 -J -R /path/to/data In this example, is passed to &man.mkisofs.8; to create an ISO 9660 file system with Joliet and Rock Ridge extensions. Refer to &man.mkisofs.8; for more details. For the initial session recording, is used for both single and multiple sessions. Replace /dev/cd0, with the name of the DVD device. Using indicates that the disk will be closed and that the recording will be unappendable. This should also provide better media compatibility with DVD-ROM drives. To burn a pre-mastered image, such as imagefile.iso, use: &prompt.root; growisofs -dvd-compat -Z /dev/cd0=imagefile.iso The write speed should be detected and automatically set according to the media and the drive being used. To force the write speed, use . Refer to &man.growisofs.1; for example usage. In order to support working files larger than 4.38GB, an UDF/ISO-9660 hybrid file system must be created by passing to &man.mkisofs.8; and all related programs, such as &man.growisofs.1;. This is required only when creating an ISO image file or when writing files directly to a disk. Since a disk created this way must be mounted as an UDF file system with &man.mount.udf.8;, it will be usable only on an UDF aware operating system. Otherwise it will look as if it contains corrupted files. To create this type of ISO file: &prompt.user; mkisofs -R -J -udf -iso-level 3 -o imagefile.iso /path/to/data To burn files directly to a disk: &prompt.root; growisofs -dvd-compat -udf -iso-level 3 -Z /dev/cd0 -J -R /path/to/data When an ISO image already contains large files, no additional options are required for &man.growisofs.1; to burn that image on a disk. Be sure to use an up-to-date version of sysutils/cdrtools, which contains &man.mkisofs.8;, as an older version may not contain large files support. If the latest version does not work, install sysutils/cdrtools-devel and read its &man.mkisofs.8;. Burning a <acronym>DVD</acronym>-Video DVD DVD-Video A DVD-Video is a specific file layout based on the ISO 9660 and micro-UDF (M-UDF) specifications. Since DVD-Video presents a specific data structure hierarchy, a particular program such as multimedia/dvdauthor is needed to author the DVD. If an image of the DVD-Video file system already exists, it can be burned in the same way as any other image. If dvdauthor was used to make the DVD and the result is in /path/to/video, the following command should be used to burn the DVD-Video: &prompt.root; growisofs -Z /dev/cd0 -dvd-video /path/to/video is passed to &man.mkisofs.8; to instruct it to create a DVD-Video file system layout. This option implies the &man.growisofs.1; option. Using a <acronym>DVD+RW</acronym> DVD DVD+RW Unlike CD-RW, a virgin DVD+RW needs to be formatted before first use. It is recommended to let &man.growisofs.1; take care of this automatically whenever appropriate. However, it is possible to use dvd+rw-format to format the DVD+RW: &prompt.root; dvd+rw-format /dev/cd0 Only perform this operation once and keep in mind that only virgin DVD+RW medias need to be formatted. Once formatted, the DVD+RW can be burned as usual. To burn a totally new file system and not just append some data onto a DVD+RW, the media does not need to be blanked first. Instead, write over the previous recording like this: &prompt.root; growisofs -Z /dev/cd0 -J -R /path/to/newdata The DVD+RW format supports appending data to a previous recording. This operation consists of merging a new session to the existing one as it is not considered to be multi-session writing. &man.growisofs.1; will grow the ISO 9660 file system present on the media. For example, to append data to a DVD+RW, use the following: &prompt.root; growisofs -M /dev/cd0 -J -R /path/to/nextdata The same &man.mkisofs.8; options used to burn the initial session should be used during next writes. Use for better media compatibility with DVD-ROM drives. When using DVD+RW, this option will not prevent the addition of data. To blank the media, use: &prompt.root; growisofs -Z /dev/cd0=/dev/zero Using a <acronym>DVD-RW</acronym> DVD DVD-RW A DVD-RW accepts two disc formats: incremental sequential and restricted overwrite. By default, DVD-RW discs are in sequential format. A virgin DVD-RW can be directly written without being formatted. However, a non-virgin DVD-RW in sequential format needs to be blanked before writing a new initial session. To blank a DVD-RW in sequential mode: &prompt.root; dvd+rw-format -blank=full /dev/cd0 A full blanking using will take about one hour on a 1x media. A fast blanking can be performed using , if the DVD-RW will be recorded in Disk-At-Once (DAO) mode. To burn the DVD-RW in DAO mode, use the command: &prompt.root; growisofs -use-the-force-luke=dao -Z /dev/cd0=imagefile.iso Since &man.growisofs.1; automatically attempts to detect fast blanked media and engage DAO write, should not be required. One should instead use restricted overwrite mode with any DVD-RW as this format is more flexible than the default of incremental sequential. To write data on a sequential DVD-RW, use the same instructions as for the other DVD formats: &prompt.root; growisofs -Z /dev/cd0 -J -R /path/to/data To append some data to a previous recording, use with &man.growisofs.1;. However, if data is appended on a DVD-RW in incremental sequential mode, a new session will be created on the disc and the result will be a multi-session disc. A DVD-RW in restricted overwrite format does not need to be blanked before a new initial session. Instead, overwrite the disc with . It is also possible to grow an existing ISO 9660 file system written on the disc with . The result will be a one-session DVD. To put a DVD-RW in restricted overwrite format, the following command must be used: &prompt.root; dvd+rw-format /dev/cd0 To change back to sequential format, use: &prompt.root; dvd+rw-format -blank=full /dev/cd0 Multi-Session Few DVD-ROM drives support multi-session DVDs and most of the time only read the first session. DVD+R, DVD-R and DVD-RW in sequential format can accept multiple sessions. The notion of multiple sessions does not exist for the DVD+RW and the DVD-RW restricted overwrite formats. Using the following command after an initial non-closed session on a DVD+R, DVD-R, or DVD-RW in sequential format, will add a new session to the disc: &prompt.root; growisofs -M /dev/cd0 -J -R /path/to/nextdata Using this command with a DVD+RW or a DVD-RW in restricted overwrite mode will append data while merging the new session to the existing one. The result will be a single-session disc. Use this method to add data after an initial write on these types of media. Since some space on the media is used between each session to mark the end and start of sessions, one should add sessions with a large amount of data to optimize media space. The number of sessions is limited to 154 for a DVD+R, about 2000 for a DVD-R, and 127 for a DVD+R Double Layer. For More Information To obtain more information about a DVD, use dvd+rw-mediainfo /dev/cd0 while the disc in the specified drive. More information about dvd+rw-tools can be found in &man.growisofs.1;, on the dvd+rw-tools web site, and in the cdwrite mailing list archives. When creating a problem report related to the use of dvd+rw-tools, always include the output of dvd+rw-mediainfo. Using a <acronym>DVD-RAM</acronym> DVD DVD-RAM DVD-RAM writers can use either a SCSI or ATAPI interface. For ATAPI devices, DMA access has to be enabled by adding the following line to /boot/loader.conf: hw.ata.atapi_dma="1" A DVD-RAM can be seen as a removable hard drive. Like any other hard drive, the DVD-RAM must be formatted before it can be used. In this example, the whole disk space will be formatted with a standard UFS2 file system: &prompt.root; dd if=/dev/zero of=/dev/acd0 bs=2k count=1 &prompt.root; bsdlabel -Bw acd0 &prompt.root; newfs /dev/acd0 The DVD device, acd0, must be changed according to the configuration. Once the DVD-RAM has been formatted, it can be mounted as a normal hard drive: &prompt.root; mount /dev/acd0 /mnt Once mounted, the DVD-RAM will be both readable and writeable. Creating and Using Floppy Disks This section explains how to format a 3.5 inch floppy disk in &os;. Steps to Format a Floppy A floppy disk needs to be low-level formatted before it can be used. This is usually done by the vendor, but formatting is a good way to check media integrity. To low-level format the floppy disk on &os;, use &man.fdformat.1;. When using this utility, make note of any error messages, as these can help determine if the disk is good or bad. To format the floppy, insert a new 3.5 inch floppy disk into the first floppy drive and issue: &prompt.root; /usr/sbin/fdformat -f 1440 /dev/fd0 After low-level formatting the disk, create a disk label as it is needed by the system to determine the size of the disk and its geometry. The supported geometry values are listed in /etc/disktab. To write the disk label, use &man.bsdlabel.8;: &prompt.root; /sbin/bsdlabel -B -w /dev/fd0 fd1440 The floppy is now ready to be high-level formatted with a file system. The floppy's file system can be either UFS or FAT, where FAT is generally a better choice for floppies. To format the floppy with FAT, issue: &prompt.root; /sbin/newfs_msdos /dev/fd0 The disk is now ready for use. To use the floppy, mount it with &man.mount.msdosfs.8;. One can also install and use emulators/mtools from the Ports Collection. Backup Basics Implementing a backup plan is essential in order to have the ability to recover from disk failure, accidental file deletion, random file corruption, or complete machine destruction, including destruction of on-site backups. The backup type and schedule will vary, depending upon the importance of the data, the granularity needed for file restores, and the amount of acceptable downtime. Some possible backup techniques include: Archives of the whole system, backed up onto permanent, off-site media. This provides protection against all of the problems listed above, but is slow and inconvenient to restore from, especially for non-privileged users. File system snapshots, which are useful for restoring deleted files or previous versions of files. Copies of whole file systems or disks which are sychronized with another system on the network using a scheduled net/rsync. Hardware or software RAID, which minimizes or avoids downtime when a disk fails. Typically, a mix of backup techniques is used. For example, one could create a schedule to automate a weekly, full system backup that is stored off-site and to supplement this backup with hourly ZFS snapshots. In addition, one could make a manual backup of individual directories or files before making file edits or deletions. This section describes some of the utilities which can be used to create and manage backups on a &os; system. File System Backups backup software dump / restore dump restore The traditional &unix; programs for backing up a file system are &man.dump.8;, which creates the backup, and &man.restore.8;, which restores the backup. These utilities work at the disk block level, below the abstractions of the files, links, and directories that are created by file systems. Unlike other backup software, dump backs up an entire file system and is unable to backup only part of a file system or a directory tree that spans multiple file systems. Instead of writing files and directories, dump writes the raw data blocks that comprise files and directories. If dump is used on the root directory, it will not back up /home, /usr or many other directories since these are typically mount points for other file systems or symbolic links into those file systems. When used to restore data, restore stores temporary files in /tmp/ by default. When using a recovery disk with a small /tmp, set TMPDIR to a directory with more free space in order for the restore to succeed. When using dump, be aware that some quirks remain from its early days in Version 6 of AT&T &unix;,circa 1975. The default parameters assume a backup to a 9-track tape, rather than to another type of media or to the high-density tapes available today. These defaults must be overridden on the command line. .rhosts It is possible to backup a file system across the network to a another system or to a tape drive attached to another computer. While the &man.rdump.8; and &man.rrestore.8; utilities can be used for this purpose, they are not considered to be secure. Instead, one can use dump and restore in a more secure fashion over an SSH connection. This example creates a full, compressed backup of the /usr file system and sends the backup file to the specified host over a SSH connection. Using <command>dump</command> over <application>ssh</application> &prompt.root; /sbin/dump -0uan -f - /usr | gzip -2 | ssh -c blowfish \ targetuser@targetmachine.example.com dd of=/mybigfiles/dump-usr-l0.gz This example sets RSH in order to write the backup to a tape drive on a remote system over a SSH connection: Using <command>dump</command> over <application>ssh</application> with <envar>RSH</envar> Set &prompt.root; env RSH=/usr/bin/ssh /sbin/dump -0uan -f targetuser@targetmachine.example.com:/dev/sa0 /usr Directory Backups backup software tar Several built-in utilities are available for backing up and restoring specified files and directories as needed. A good choice for making a backup of all of the files in a directory is &man.tar.1;. This utility dates back to Version 6 of AT&T &unix; and by default assumes a recursive backup to a local tape device. Switches can be used to instead specify the name of a backup file. tar This example creates a compressed backup of the current directory and saves it to /tmp/mybackup.tgz. When creating a backup file, make sure that the backup is not saved to the same directory that is being backed up. Backing Up the Current Directory With <command>tar</command> &prompt.root; tar czvf /tmp/mybackup.tgz . To restore the entire backup, cd into the directory to restore into and specify the name of the backup. Note that this will overwrite any newer versions of files in the restore directory. When in doubt, restore to a temporary directory or specify the name of the file within the backup to restore. Restoring Up the Current Directory With <command>tar</command> &prompt.root; tar xzvf /tmp/mybackup.tgz There are dozens of available switches which are described in &man.tar.1;. This utility also supports the use of exclude patterns to specify which files should not be included when backing up the specified directory or restoring files from a backup. backup software cpio To create a backup using a specified list of files and directories, &man.cpio.1; is a good choice. Unlike tar, cpio does not know how to walk the directory tree and it must be provided the list of files to backup. For example, a list of files can be created using ls or find. This example creates a recursive listing of the current directory which is then piped to cpio in order to create an output backup file named /tmp/mybackup.cpio. Using<command>ls</command> and <command>cpio</command> to Make a Recursive Backup of the Current Directory &prompt.root; ls -R | cpio -ovF /tmp/mybackup.cpio backup software pax pax POSIX IEEE A backup utility which tries to bridge the features provided by tar and cpio is &man.pax.1;. Over the years, the various versions of tar and cpio became slightly incompatible. &posix; created pax which attempts to read and write many of the various cpio and tar formats, plus new formats of its own. The pax equivalent to the previous examples would be: Backing Up the Current Directory With <command>pax</command> &prompt.root; pax -wf /tmp/mybackup.pax . Using Data Tapes for Backups tape media While tape technology has continued to evolve, modern backup systems tend to combine off-site backups with local removable media. &os; supports any tape drive that uses SCSI, such as LTO or DAT. There is limited support for SATA and USB tape drives. For SCSI tape devices, &os; uses the &man.sa.4; driver and the /dev/sa0, /dev/nsa0, and /dev/esa0 devices. The physical device name is /dev/sa0. When /dev/nsa0 is used, the backup application will not rewind the tape after writing a file, which allows writing more than one file to a tape. Using /dev/esa0 ejects the tape after the device is closed. In &os;, mt is used to control operations of the tape drive, such as seeking through files on a tape or writing tape control marks to the tape. For example, the first three files on a tape can be preserved by skipping past them before writing a new file: &prompt.root; mt -f /dev/nsa0 fsf 3 This utility supports many operations. Refer to &man.mt.1; for details. To write a single file to tape using tar, specify the name of the tape device and the file to backup: &prompt.root; tar cvf /dev/sa0 file To recover files from a tar archive on tape into the current directory: &prompt.root; tar xvf /dev/sa0 To backup a UFS file system, use dump. This examples backs up /usr without rewinding the tape when finished: &prompt.root; dump -0aL -b64 -f /dev/nsa0 /usr To interactively restore files from a dump file on tape into the current directory: &prompt.root; restore -i -f /dev/nsa0 Third-Party Backup Utilities backup software The &os; Ports Collection provides many third-party utilities which can be used to schedule the creation of backups, simplify tape backup, and make backups easier and more convenient. Many of these applications are client/server based and can be used to automate the backups of a single system or all of the computers in a network. Popular utilities include Amanda, Bacula, rsync, and duplicity. Emergency Recovery In addition to regular backups, it is recommended to perform the following steps as part of an emergency preparedness plan. bsdlabel Create a print copy of the output of the following commands: gpart show more /etc/fstab dmesg livefs CD Store this printout and a copy of the installation media in a secure location. Should an emergency restore be needed, boot into the installation media and select Live CD to access a rescue shell. This rescue mode can be used to view the current state of the system, and if needed, to reformat disks and restore data from backups. The installation media for &os;/&arch.i386; &rel2.current;-RELEASE does not include a rescue shell. For this version, instead download and burn a Livefs CD image from ftp://ftp.FreeBSD.org/pub/FreeBSD/releases/&arch.i386;/ISO-IMAGES/&rel2.current;/&os;-&rel2.current;-RELEASE-&arch.i386;-livefs.iso. Next, test the rescue shell and the backups. Make notes of the procedure. Store these notes with the media, the printouts, and the backups. These notes may prevent the inadvertent destruction of the backups while under the stress of performing an emergency recovery. For an added measure of security, store the latest backup at a remote location which is physically separated from the computers and disk drives by a significant distance. Memory Disks Marc Fonvieille Reorganized and enhanced by In addition to physical disks, &os; also supports the creation and use of memory disks. One possible use for a memory disk is to access the contents of an ISO file system without the overhead of first burning it to a CD or DVD, then mounting the CD/DVD media. In &os;, the &man.md.4; driver is used to provide support for memory disks. The GENERIC kernel includes this driver. When using a custom kernel configuration file, ensure it includes this line: device md Attaching and Detaching Existing Images disks memory To mount an existing file system image, use mdconfig to specify the name of the ISO file and a free unit number. Then, refer to that unit number to mount it on an existing mount point. Once mounted, the files in the ISO will appear in the mount point. This example attaches diskimage.iso to the memory device /dev/md0 then mounts that memory device on /mnt: &prompt.root; mdconfig -f diskimage.iso -u 0 &prompt.root; mount /dev/md0 /mnt If a unit number is not specified with , mdconfig will automatically allocate an unused memory device and output the name of the allocated unit, such as md4. Refer to &man.mdconfig.8; for more details about this command and its options. disks detaching a memory disk When a memory disk is no longer in use, its resources should be released back to the system. First, unmount the file system, then use mdconfig to detach the disk from the system and release its resources. To continue this example: &prompt.root; umount /mnt &prompt.root; mdconfig -d -u 0 To determine if any memory disks are still attached to the system, type mdconfig -l. Creating a File- or Memory-Backed Memory Disk disks memory file system &os; also supports memory disks where the storage to use is allocated from either a hard disk or an area of memory. The first method is commonly referred to as a file-backed file system and the second method as a memory-backed file system. Both types can be created using mdconfig. To create a new memory-backed file system, specify a type of swap and the size of the memory disk to create. Then, format the memory disk with a file system and mount as usual. This example creates a 5M memory disk on unit 1. That memory disk is then formatted with the UFS file system before it is mounted: &prompt.root; mdconfig -a -t swap -s 5m -u 1 &prompt.root; newfs -U md1 /dev/md1: 5.0MB (10240 sectors) block size 16384, fragment size 2048 using 4 cylinder groups of 1.27MB, 81 blks, 192 inodes. with soft updates super-block backups (for fsck -b #) at: 160, 2752, 5344, 7936 &prompt.root; mount /dev/md1 /mnt &prompt.root; df /mnt Filesystem 1K-blocks Used Avail Capacity Mounted on /dev/md1 4718 4 4338 0% /mnt To create a new file-backed memory disk, first allocate an area of disk to use. This example creates an empty 5K file named newimage: &prompt.root; dd if=/dev/zero of=newimage bs=1k count=5k 5120+0 records in 5120+0 records out Next, attach that file to a memory disk, label the memory disk and format it with the UFS file system, mount the memory disk, and verify the size of the file-backed disk: &prompt.root; mdconfig -f newimage -u 0 &prompt.root; bsdlabel -w md0 auto &prompt.root; newfs md0a /dev/md0a: 5.0MB (10224 sectors) block size 16384, fragment size 2048 using 4 cylinder groups of 1.25MB, 80 blks, 192 inodes. super-block backups (for fsck -b #) at: 160, 2720, 5280, 7840 &prompt.root; mount /dev/md0a /mnt &prompt.root; df /mnt Filesystem 1K-blocks Used Avail Capacity Mounted on /dev/md0a 4710 4 4330 0% /mnt It takes several commands to create a file- or memory-backed file system using mdconfig. &os; also comes with mdmfs which automatically configures a memory disk, formats it with the UFS file system, and mounts it. For example, after creating newimage with dd, this one command is equivalent to running the bsdlabel, newfs, and mount commands shown above: &prompt.root; mdmfs -F newimage -s 5m md0 /mnt To instead create a new memory-based memory disk with mdmfs, use this one command: &prompt.root; mdmfs -s 5m md1 /mnt If the unit number is not specified, mdmfs will automatically select an unused memory device. For more details about mdmfs, refer to &man.mdmfs.8;. File System Snapshots Tom Rhodes Contributed by file systems snapshots &os; offers a feature in conjunction with Soft Updates: file system snapshots. UFS snapshots allow a user to create images of specified file systems, and treat them as a file. Snapshot files must be created in the file system that the action is performed on, and a user may create no more than 20 snapshots per file system. Active snapshots are recorded in the superblock so they are persistent across unmount and remount operations along with system reboots. When a snapshot is no longer required, it can be removed using &man.rm.1;. While snapshots may be removed in any order, all the used space may not be acquired because another snapshot will possibly claim some of the released blocks. The un-alterable file flag is set by &man.mksnap.ffs.8; after initial creation of a snapshot file. &man.unlink.1; makes an exception for snapshot files since it allows them to be removed. Snapshots are created using &man.mount.8;. To place a snapshot of /var in the file /var/snapshot/snap, use the following command: &prompt.root; mount -u -o snapshot /var/snapshot/snap /var Alternatively, use &man.mksnap.ffs.8; to create the snapshot: &prompt.root; mksnap_ffs /var /var/snapshot/snap One can find snapshot files on a file system, such as /var, using &man.find.1;: &prompt.root; find /var -flags snapshot Once a snapshot has been created, it has several uses: Some administrators will use a snapshot file for backup purposes, because the snapshot can be transferred to CDs or tape. The file system integrity checker, &man.fsck.8;, may be run on the snapshot. Assuming that the file system was clean when it was mounted, this should always provide a clean and unchanging result. Running &man.dump.8; on the snapshot will produce a dump file that is consistent with the file system and the timestamp of the snapshot. &man.dump.8; can also take a snapshot, create a dump image, and then remove the snapshot in one command by using . The snapshot can be mounted as a frozen image of the file system. To &man.mount.8; the snapshot /var/snapshot/snap run: &prompt.root; mdconfig -a -t vnode -f /var/snapshot/snap -u 4 &prompt.root; mount -r /dev/md4 /mnt The frozen /var is now available through /mnt. Everything will initially be in the same state it was during the snapshot creation time. The only exception is that any earlier snapshots will appear as zero length files. To unmount the snapshot, use: &prompt.root; umount /mnt &prompt.root; mdconfig -d -u 4 For more information about and file system snapshots, including technical papers, visit Marshall Kirk McKusick's website at http://www.mckusick.com/. Disk Quotas accounting disk space disk quotas Disk quotas can be used to limit the amount of disk space or the number of files a user or members of a group may allocate on a per-file system basis. This prevents one user or group of users from consuming all of the available disk space. This section describes how to configure disk quotas for the UFS file system. To configure quotas on the ZFS file system, refer to Enabling Disk Quotas To determine if the &os; kernel provides support for disk quotas: &prompt.user; sysctl kern.features.ufs_quota kern.features.ufs_quota: 1 In this example, the 1 indicates quota support. If the value is instead 0, add the following line to a custom kernel configuration file and rebuild the kernel using the instructions in : options QUOTA Next, enable disk quotas in /etc/rc.conf: quota_enable="YES" disk quotas checking Normally on bootup, the quota integrity of each file system is checked by &man.quotacheck.8;. This program insures that the data in the quota database properly reflects the data on the file system. This is a time consuming process that will significantly affect the time the system takes to boot. To skip this step, add this variable to /etc/rc.conf: check_quotas="NO" Finally, edit /etc/fstab to enable disk quotas on a per-file system basis. To enable per-user quotas on a file system, add to the options field in the /etc/fstab entry for the file system to enable quotas on. For example: /dev/da1s2g /home ufs rw,userquota 1 2 To enable group quotas, use instead. To enable both user and group quotas, separate the options with a comma: /dev/da1s2g /home ufs rw,userquota,groupquota 1 2 By default, quota files are stored in the root directory of the file system as quota.user and quota.group. Refer to &man.fstab.5; for more information. Specifying an alternate location for the quota files is not recommended. Once the configuration is complete, reboot the system and /etc/rc will automatically run the appropriate commands to create the initial quota files for all of the quotas enabled in /etc/fstab. In the normal course of operations, there should be no need to manually run &man.quotacheck.8;, &man.quotaon.8;, or &man.quotaoff.8;. However, one should read these manual pages to be familiar with their operation. Setting Quota Limits disk quotas limits To verify that quotas are enabled, run: &prompt.root; quota -v There should be a one line summary of disk usage and current quota limits for each file system that quotas are enabled on. The system is now ready to be assigned quota limits with edquota. Several options are available to enforce limits on the amount of disk space a user or group may allocate, and how many files they may create. Allocations can be limited based on disk space (block quotas), number of files (inode quotas), or a combination of both. Each limit is further broken down into two categories: hard and soft limits. hard limit A hard limit may not be exceeded. Once a user reaches a hard limit, no further allocations can be made on that file system by that user. For example, if the user has a hard limit of 500 kbytes on a file system and is currently using 490 kbytes, the user can only allocate an additional 10 kbytes. Attempting to allocate an additional 11 kbytes will fail. soft limit Soft limits can be exceeded for a limited amount of time, known as the grace period, which is one week by default. If a user stays over their limit longer than the grace period, the soft limit turns into a hard limit and no further allocations are allowed. When the user drops back below the soft limit, the grace period is reset. In the following example, the quota for the test account is being edited. When edquota is invoked, the editor specified by EDITOR is opened in order to edit the quota limits. The default editor is set to vi. &prompt.root; edquota -u test Quotas for user test: /usr: kbytes in use: 65, limits (soft = 50, hard = 75) inodes in use: 7, limits (soft = 50, hard = 60) /usr/var: kbytes in use: 0, limits (soft = 50, hard = 75) inodes in use: 0, limits (soft = 50, hard = 60) There are normally two lines for each file system that has quotas enabled. One line represents the block limits and the other represents the inode limits. Change the value to modify the quota limit. For example, to raise the block limit on /usr to a soft limit of 500 and a hard limit of 600, change the values in that line as follows: /usr: kbytes in use: 65, limits (soft = 500, hard = 600) The new quota limits take affect upon exiting the editor. Sometimes it is desirable to set quota limits on a range of users. This can be done by first assigning the desired quota limit to a user. Then, use to duplicate that quota to a specified range of user IDs (UIDs). The following command will duplicate those quota limits for UIDs 10,000 through 19,999: &prompt.root; edquota -p test 10000-19999 For more information, refer to &man.edquota.8;. Checking Quota Limits and Disk Usage disk quotas checking To check individual user or group quotas and disk usage, use &man.quota.1;. A user may only examine their own quota and the quota of a group they are a member of. Only the superuser may view all user and group quotas. To get a summary of all quotas and disk usage for file systems with quotas enabled, use &man.repquota.8;. Normally, file systems that the user is not using any disk space on will not show in the output of quota, even if the user has a quota limit assigned for that file system. Use to display those file systems. The following is sample output from quota -v for a user that has quota limits on two file systems. Disk quotas for user test (uid 1002): Filesystem usage quota limit grace files quota limit grace /usr 65* 50 75 5days 7 50 60 /usr/var 0 50 75 0 50 60 grace period In this example, the user is currently 15 kbytes over the soft limit of 50 kbytes on /usr and has 5 days of grace period left. The asterisk * indicates that the user is currently over the quota limit. Quotas over NFS NFS Quotas are enforced by the quota subsystem on the NFS server. The &man.rpc.rquotad.8; daemon makes quota information available to quota on NFS clients, allowing users on those machines to see their quota statistics. On the NFS server, enable rpc.rquotad by removing the # from this line in /etc/inetd.conf: rquotad/1 dgram rpc/udp wait root /usr/libexec/rpc.rquotad rpc.rquotad Then, restart inetd: &prompt.root; service inetd restart Encrypting Disk Partitions Lucky Green Contributed by
shamrock@cypherpunks.to
disks encrypting &os; offers excellent online protections against unauthorized data access. File permissions and Mandatory Access Control (MAC) help prevent unauthorized users from accessing data while the operating system is active and the computer is powered up. However, the permissions enforced by the operating system are irrelevant if an attacker has physical access to a computer and can move the computer's hard drive to another system to copy and analyze the data. Regardless of how an attacker may have come into possession of a hard drive or powered-down computer, the GEOM-based cryptographic subsystems built into &os; are able to protect the data on the computer's file systems against even highly-motivated attackers with significant resources. Unlike encryption methods that encrypt individual files, the built-in gbde and geli utilities can be used to transparently encrypt entire file systems. No cleartext ever touches the hard drive's platter. This chapter demonstrates how to create an encrypted file system on &os;. It first demonstrates the process using gbde and then demonstrates the same example using geli. Disk Encryption with <application>gbde</application> The objective of the &man.gbde.4; facility is to provide a formidable challenge for an attacker to gain access to the contents of a cold storage device. However, if the computer is compromised while up and running and the storage device is actively attached, or the attacker has access to a valid passphrase, it offers no protection to the contents of the storage device. Thus, it is important to provide physical security while the system is running and to protect the passphrase used by the encryption mechanism. This facility provides several barriers to protect the data stored in each disk sector. It encrypts the contents of a disk sector using 128-bit AES in CBC mode. Each sector on the disk is encrypted with a different AES key. For more information on the cryptographic design, including how the sector keys are derived from the user-supplied passphrase, refer to &man.gbde.4;. &os; provides a kernel module for gbde which can be loaded with this command: &prompt.root; kldload geom_bde If using a custom kernel configuration file, ensure it contains this line: options GEOM_BDE The following example demonstrates adding a new hard drive to a system that will hold a single encrypted partition that will be mounted as /private. Encrypting a Partition with <application>gbde</application> Add the New Hard Drive Install the new drive to the system as explained in . For the purposes of this example, a new hard drive partition has been added as /dev/ad4s1c and /dev/ad0s1* represents the existing standard &os; partitions. &prompt.root; ls /dev/ad* /dev/ad0 /dev/ad0s1b /dev/ad0s1e /dev/ad4s1 /dev/ad0s1 /dev/ad0s1c /dev/ad0s1f /dev/ad4s1c /dev/ad0s1a /dev/ad0s1d /dev/ad4 Create a Directory to Hold <command>gbde</command> Lock Files &prompt.root; mkdir /etc/gbde The gbde lock file contains information that gbde requires to access encrypted partitions. Without access to the lock file, gbde will not be able to decrypt the data contained in the encrypted partition without significant manual intervention which is not supported by the software. Each encrypted partition uses a separate lock file. Initialize the <command>gbde</command> Partition A gbde partition must be initialized before it can be used. This initialization needs to be performed only once. This command will open the default editor, in order to set various configuration options in a template. For use with the UFS file system, set the sector_size to 2048: &prompt.root; gbde init /dev/ad4s1c -i -L /etc/gbde/ad4s1c.lock# $FreeBSD: src/sbin/gbde/template.txt,v 1.1.36.1 2009/08/03 08:13:06 kensmith Exp $ # # Sector size is the smallest unit of data which can be read or written. # Making it too small decreases performance and decreases available space. # Making it too large may prevent filesystems from working. 512 is the # minimum and always safe. For UFS, use the fragment size # sector_size = 2048 [...] Once the edit is saved, the user will be asked twice to type the passphrase used to secure the data. The passphrase must be the same both times. The ability of gbde to protect data depends entirely on the quality of the passphrase. For tips on how to select a secure passphrase that is easy to remember, see http://world.std.com/~reinhold/diceware.htm. This initialization creates a lock file for the gbde partition. In this example, it is stored as /etc/gbde/ad4s1c.lock. Lock files must end in .lock in order to be correctly detected by the /etc/rc.d/gbde start up script. Lock files must be backed up together with the contents of any encrypted partitions. Without the lock file, the legitimate owner will be unable to access the data on the encrypted partition. Attach the Encrypted Partition to the Kernel &prompt.root; gbde attach /dev/ad4s1c -l /etc/gbde/ad4s1c.lock This command will prompt to input the passphrase that was selected during the initialization of the encrypted partition. The new encrypted device will appear in /dev as /dev/device_name.bde: &prompt.root; ls /dev/ad* /dev/ad0 /dev/ad0s1b /dev/ad0s1e /dev/ad4s1 /dev/ad0s1 /dev/ad0s1c /dev/ad0s1f /dev/ad4s1c /dev/ad0s1a /dev/ad0s1d /dev/ad4 /dev/ad4s1c.bde Create a File System on the Encrypted Device Once the encrypted device has been attached to the kernel, a file system can be created on the device. This example creates a UFS file system with soft updates enabled. Be sure to specify the partition which has a *.bde extension: &prompt.root; newfs -U /dev/ad4s1c.bde Mount the Encrypted Partition Create a mount point and mount the encrypted file system: &prompt.root; mkdir /private &prompt.root; mount /dev/ad4s1c.bde /private Verify That the Encrypted File System is Available The encrypted file system should now be visible and available for use: &prompt.user; df -H Filesystem Size Used Avail Capacity Mounted on /dev/ad0s1a 1037M 72M 883M 8% / /devfs 1.0K 1.0K 0B 100% /dev /dev/ad0s1f 8.1G 55K 7.5G 0% /home /dev/ad0s1e 1037M 1.1M 953M 0% /tmp /dev/ad0s1d 6.1G 1.9G 3.7G 35% /usr /dev/ad4s1c.bde 150G 4.1K 138G 0% /private After each boot, any encrypted file systems must be manually re-attached to the kernel, checked for errors, and mounted, before the file systems can be used. To configure these steps, add the following lines to /etc/rc.conf: gbde_autoattach_all="YES" gbde_devices="ad4s1c" gbde_lockdir="/etc/gbde" This requires that the passphrase be entered at the console at boot time. After typing the correct passphrase, the encrypted partition will be mounted automatically. Additional gbde boot options are available and listed in &man.rc.conf.5;. sysinstall is incompatible with gbde-encrypted devices. All *.bde devices must be detached from the kernel before starting sysinstall or it will crash during its initial probing for devices. To detach the encrypted device used in the example, use the following command: &prompt.root; gbde detach /dev/ad4s1c Disk Encryption with <command>geli</command> Daniel Gerzo Contributed by An alternative cryptographic GEOM class is available using geli. This control utility adds some features and uses a different scheme for doing cryptographic work. It provides the following features: Utilizes the &man.crypto.9; framework and automatically uses cryptographic hardware when it is available. Supports multiple cryptographic algorithms such as AES, Blowfish, and 3DES. Allows the root partition to be encrypted. The passphrase used to access the encrypted root partition will be requested during system boot. Allows the use of two independent keys. It is fast as it performs simple sector-to-sector encryption. Allows backup and restore of master keys. If a user destroys their keys, it is still possible to get access to the data by restoring keys from the backup. Allows a disk to attach with a random, one-time key which is useful for swap partitions and temporary file systems. More features and usage examples can be found in &man.geli.8;. The following example describes how to generate a key file which will be used as part of the master key for the encrypted provider mounted under /private. The key file will provide some random data used to encrypt the master key. The master key will also be protected by a passphrase. The provider's sector size will be 4kB. The example describes how to attach to the geli provider, create a file system on it, mount it, work with it, and finally, how to detach it. Encrypting a Partition with <command>geli</command> Load <command>geli</command> Support Support for geli is built into the GENERIC kernel. To configure the system to automatically load the module at boot time, add the following line to /boot/loader.conf: geom_eli_load="YES" To load the kernel module now: &prompt.root; kldload geom_eli For a custom kernel, ensure the kernel configuration file contains these lines: options GEOM_ELI device crypto Generate the Master Key The following commands generate a master key (/root/da2.key) that is protected with a passphrase. The data source for the key file is /dev/random and the sector size of the provider (/dev/da2.eli) is 4kB as a bigger sector size provides better performance: &prompt.root; dd if=/dev/random of=/root/da2.key bs=64 count=1 &prompt.root; geli init -s 4096 -K /root/da2.key /dev/da2 Enter new passphrase: Reenter new passphrase: It is not mandatory to use both a passphrase and a key file as either method of securing the master key can be used in isolation. If the key file is given as -, standard input will be used. For example, this command generates three key files: &prompt.root; cat keyfile1 keyfile2 keyfile3 | geli init -K - /dev/da2 Attach the Provider with the Generated Key To attach the provider, specify the key file, the name of the disk, and the passphrase: &prompt.root; geli attach -k /root/da2.key /dev/da2 Enter passphrase: This creates a new device with an .eli extension: &prompt.root; ls /dev/da2* /dev/da2 /dev/da2.eli Create the New File System Next, format the device with the UFS file system and mount it on an existing mount point: &prompt.root; dd if=/dev/random of=/dev/da2.eli bs=1m &prompt.root; newfs /dev/da2.eli &prompt.root; mount /dev/da2.eli /private The encrypted file system should now be available for use: &prompt.root; df -H Filesystem Size Used Avail Capacity Mounted on /dev/ad0s1a 248M 89M 139M 38% / /devfs 1.0K 1.0K 0B 100% /dev /dev/ad0s1f 7.7G 2.3G 4.9G 32% /usr /dev/ad0s1d 989M 1.5M 909M 0% /tmp /dev/ad0s1e 3.9G 1.3G 2.3G 35% /var /dev/da2.eli 150G 4.1K 138G 0% /private Once the work on the encrypted partition is done, and the /private partition is no longer needed, it is prudent to put the device into cold storage by unmounting and detaching the geli encrypted partition from the kernel: &prompt.root; umount /private &prompt.root; geli detach da2.eli An rc.d script is provided to simplify the mounting of geli-encrypted devices at boot time. For this example, add these lines to /etc/rc.conf: geli_devices="da2" geli_da2_flags="-p -k /root/da2.key" This configures /dev/da2 as a geli provider with a master key of /root/da2.key. The system will automatically detach the provider from the kernel before the system shuts down. During the startup process, the script will prompt for the passphrase before attaching the provider. Other kernel messages might be shown before and after the password prompt. If the boot process seems to stall, look carefully for the password prompt among the other messages. Once the correct passphrase is entered, the provider is attached. The file system is then mounted, typically by an entry in /etc/fstab. Refer to for instructions on how to configure a file system to mount at boot time. Encrypting Swap Christian Brüffer Written by swap encrypting Like the encryption of disk partitions, encryption of swap space is used to protect sensitive information. Consider an application that deals with passwords. As long as these passwords stay in physical memory, they are not written to disk and will be cleared after a reboot. However, if &os; starts swapping out memory pages to free space, the passwords may be written to the disk unencrypted. Encrypting swap space can be a solution for this scenario. This section demonstrates how to configure an encrypted swap partition using &man.gbde.8; or &man.geli.8; encryption. It assumes a UFS file system where /dev/ad0s1b is the swap partition. Configuring Encrypted Swap Swap partitions are not encrypted by default and should be cleared of any sensitive data before continuing. To overwrite the current swap partition with random garbage, execute the following command: &prompt.root; dd if=/dev/random of=/dev/ad0s1b bs=1m To encrypt the swap partition using &man.gbde.8;, add the .bde suffix to the swap line in /etc/fstab: # Device Mountpoint FStype Options Dump Pass# /dev/ad0s1b.bde none swap sw 0 0 To instead encrypt the swap partition using &man.geli.8;, use the .eli suffix: # Device Mountpoint FStype Options Dump Pass# /dev/ad0s1b.eli none swap sw 0 0 By default, &man.geli.8; uses the AES algorithm with a key length of 128 bit. These defaults can be altered by using geli_swap_flags in /etc/rc.conf. The following flags configure encryption using the Blowfish algorithm with a key length of 128 bits and a sectorsize of 4 kilobytes, and sets detach on last close: geli_swap_flags="-e blowfish -l 128 -s 4096 -d" Refer to the description of onetime in &man.geli.8; for a list of possible options. Encrypted Swap Verification Once the system has rebooted, proper operation of the encrypted swap can be verified using swapinfo. If &man.gbde.8; is being used: &prompt.user; swapinfo Device 1K-blocks Used Avail Capacity /dev/ad0s1b.bde 542720 0 542720 0% If &man.geli.8; is being used: &prompt.user; swapinfo Device 1K-blocks Used Avail Capacity /dev/ad0s1b.eli 542720 0 542720 0% Highly Available Storage (<acronym>HAST</acronym>) Daniel Gerzo Contributed by Freddie Cash With inputs from Pawel Jakub Dawidek Michael W. Lucas Viktor Petersson HAST high availability High availability is one of the main requirements in serious business applications and highly-available storage is a key component in such environments. In &os;, the Highly Available STorage (HAST) framework allows transparent storage of the same data across several physically separated machines connected by a TCP/IP network. HAST can be understood as a network-based RAID1 (mirror), and is similar to the DRBD® storage system used in the GNU/&linux; platform. In combination with other high-availability features of &os; like CARP, HAST makes it possible to build a highly-available storage cluster that is resistant to hardware failures. The following are the main features of HAST: Can be used to mask I/O errors on local hard drives. File system agnostic as it works with any file system supported by &os;. Efficient and quick resynchronization as only the blocks that were modified during the downtime of a node are synchronized. Can be used in an already deployed environment to add additional redundancy. Together with CARP, Heartbeat, or other tools, it can be used to build a robust and durable storage system. After reading this section, you will know: What HAST is, how it works, and which features it provides. How to set up and use HAST on &os;. How to integrate CARP and &man.devd.8; to build a robust storage system. Before reading this section, you should: Understand &unix; and &os; basics (). Know how to configure network interfaces and other core &os; subsystems (). Have a good understanding of &os; networking (). The HAST project was sponsored by The &os; Foundation with support from http://www.omc.net/ and http://www.transip.nl/. HAST Operation HAST provides synchronous block-level replication between two physical machines: the primary, also known as the master node, and the secondary, or slave node. These two machines together are referred to as a cluster. Since HAST works in a primary-secondary configuration, it allows only one of the cluster nodes to be active at any given time. The primary node, also called active, is the one which will handle all the I/O requests to HAST-managed devices. The secondary node is automatically synchronized from the primary node. The physical components of the HAST system are the local disk on primary node, and the disk on the remote, secondary node. HAST operates synchronously on a block level, making it transparent to file systems and applications. HAST provides regular GEOM providers in /dev/hast/ for use by other tools or applications. There is no difference between using HAST-provided devices and raw disks or partitions. Each write, delete, or flush operation is sent to both the local disk and to the remote disk over TCP/IP. Each read operation is served from the local disk, unless the local disk is not up-to-date or an I/O error occurs. In such cases, the read operation is sent to the secondary node. HAST tries to provide fast failure recovery. For this reason, it is important to reduce synchronization time after a node's outage. To provide fast synchronization, HAST manages an on-disk bitmap of dirty extents and only synchronizes those during a regular synchronization, with an exception of the initial sync. There are many ways to handle synchronization. HAST implements several replication modes to handle different synchronization methods: memsync: This mode reports a write operation as completed when the local write operation is finished and when the remote node acknowledges data arrival, but before actually storing the data. The data on the remote node will be stored directly after sending the acknowledgement. This mode is intended to reduce latency, but still provides good reliability. fullsync: This mode reports a write operation as completed when both the local write and the remote write complete. This is the safest and the slowest replication mode. This mode is the default. async: This mode reports a write operation as completed when the local write completes. This is the fastest and the most dangerous replication mode. It should only be used when replicating to a distant node where latency is too high for other modes. HAST Configuration The HAST framework consists of several components: The &man.hastd.8; daemon which provides data synchronization. When this daemon is started, it will automatically load geom_gate.ko. The userland management utility, &man.hastctl.8;. The &man.hast.conf.5; configuration file. This file must exist before starting hastd. Users who prefer to statically build GEOM_GATE support into the kernel should add this line to the custom kernel configuration file, then rebuild the kernel using the instructions in : options GEOM_GATE The following example describes how to configure two nodes in master-slave/primary-secondary operation using HAST to replicate the data between the two. The nodes will be called hasta, with an IP address of 172.16.0.1, and hastb, with an IP address of 172.16.0.2. Both nodes will have a dedicated hard drive /dev/ad6 of the same size for HAST operation. The HAST pool, sometimes referred to as a resource or the GEOM provider in /dev/hast/, will be called test. Configuration of HAST is done using /etc/hast.conf. This file should be identical on both nodes. The simplest configuration is: resource test { on hasta { local /dev/ad6 remote 172.16.0.2 } on hastb { local /dev/ad6 remote 172.16.0.1 } } For more advanced configuration, refer to &man.hast.conf.5;. It is also possible to use host names in the remote statements if the hosts are resolvable and defined either in /etc/hosts or in the local DNS. Once the configuration exists on both nodes, the HAST pool can be created. Run these commands on both nodes to place the initial metadata onto the local disk and to start &man.hastd.8;: &prompt.root; hastctl create test &prompt.root; service hastd onestart It is not possible to use GEOM providers with an existing file system or to convert an existing storage to a HAST-managed pool. This procedure needs to store some metadata on the provider and there will not be enough required space available on an existing provider. A HAST node's primary or secondary role is selected by an administrator, or software like Heartbeat, using &man.hastctl.8;. On the primary node, hasta, issue this command: &prompt.root; hastctl role primary test Run this command on the secondary node, hastb: &prompt.root; hastctl role secondary test Verify the result by running hastctl on each node: &prompt.root; hastctl status test Check the status line in the output. If it says degraded, something is wrong with the configuration file. It should say complete on each node, meaning that the synchronization between the nodes has started. The synchronization completes when hastctl status reports 0 bytes of dirty extents. The next step is to create a file system on the GEOM provider and mount it. This must be done on the primary node. Creating the file system can take a few minutes, depending on the size of the hard drive. This example creates a UFS file system on /dev/hast/test: &prompt.root; newfs -U /dev/hast/test &prompt.root; mkdir /hast/test &prompt.root; mount /dev/hast/test /hast/test Once the HAST framework is configured properly, the final step is to make sure that HAST is started automatically during system boot. Add this line to /etc/rc.conf: hastd_enable="YES" Failover Configuration The goal of this example is to build a robust storage system which is resistant to the failure of any given node. If the primary node fails, the secondary node is there to take over seamlessly, check and mount the file system, and continue to work without missing a single bit of data. To accomplish this task, the Common Address Redundancy Protocol (CARP) is used to provide for automatic failover at the IP layer. CARP allows multiple hosts on the same network segment to share an IP address. Set up CARP on both nodes of the cluster according to the documentation available in . In this example, each node will have its own management IP address and a shared IP address of 172.16.0.254. The primary HAST node of the cluster must be the master CARP node. The HAST pool created in the previous section is now ready to be exported to the other hosts on the network. This can be accomplished by exporting it through NFS or Samba, using the shared IP address 172.16.0.254. The only problem which remains unresolved is an automatic failover should the primary node fail. In the event of CARP interfaces going up or down, the &os; operating system generates a &man.devd.8; event, making it possible to watch for state changes on the CARP interfaces. A state change on the CARP interface is an indication that one of the nodes failed or came back online. These state change events make it possible to run a script which will automatically handle the HAST failover. To catch state changes on the CARP interfaces, add this configuration to /etc/devd.conf on each node: notify 30 { match "system" "IFNET"; match "subsystem" "carp0"; match "type" "LINK_UP"; action "/usr/local/sbin/carp-hast-switch master"; }; notify 30 { match "system" "IFNET"; match "subsystem" "carp0"; match "type" "LINK_DOWN"; action "/usr/local/sbin/carp-hast-switch slave"; }; If the systems are running &os; 10 or higher, replace carp0 with the name of the CARP-configured interface. Restart &man.devd.8; on both nodes to put the new configuration into effect: &prompt.root; service devd restart When the specified interface state changes by going up or down , the system generates a notification, allowing the &man.devd.8; subsystem to run the specified automatic failover script, /usr/local/sbin/carp-hast-switch. For further clarification about this configuration, refer to &man.devd.conf.5;. Here is an example of an automated failover script: #!/bin/sh # Original script by Freddie Cash <fjwcash@gmail.com> # Modified by Michael W. Lucas <mwlucas@BlackHelicopters.org> # and Viktor Petersson <vpetersson@wireload.net> # The names of the HAST resources, as listed in /etc/hast.conf resources="test" # delay in mounting HAST resource after becoming master # make your best guess delay=3 # logging log="local0.debug" name="carp-hast" # end of user configurable stuff case "$1" in master) logger -p $log -t $name "Switching to primary provider for ${resources}." sleep ${delay} # Wait for any "hastd secondary" processes to stop for disk in ${resources}; do while $( pgrep -lf "hastd: ${disk} \(secondary\)" > /dev/null 2>&1 ); do sleep 1 done # Switch role for each disk hastctl role primary ${disk} if [ $? -ne 0 ]; then logger -p $log -t $name "Unable to change role to primary for resource ${disk}." exit 1 fi done # Wait for the /dev/hast/* devices to appear for disk in ${resources}; do for I in $( jot 60 ); do [ -c "/dev/hast/${disk}" ] && break sleep 0.5 done if [ ! -c "/dev/hast/${disk}" ]; then logger -p $log -t $name "GEOM provider /dev/hast/${disk} did not appear." exit 1 fi done logger -p $log -t $name "Role for HAST resources ${resources} switched to primary." logger -p $log -t $name "Mounting disks." for disk in ${resources}; do mkdir -p /hast/${disk} fsck -p -y -t ufs /dev/hast/${disk} mount /dev/hast/${disk} /hast/${disk} done ;; slave) logger -p $log -t $name "Switching to secondary provider for ${resources}." # Switch roles for the HAST resources for disk in ${resources}; do if ! mount | grep -q "^/dev/hast/${disk} on " then else umount -f /hast/${disk} fi sleep $delay hastctl role secondary ${disk} 2>&1 if [ $? -ne 0 ]; then logger -p $log -t $name "Unable to switch role to secondary for resource ${disk}." exit 1 fi logger -p $log -t $name "Role switched to secondary for resource ${disk}." done ;; esac In a nutshell, the script takes these actions when a node becomes master: Promotes the HAST pool to primary on the other node. Checks the file system under the HAST pool. Mounts the pool. When a node becomes secondary: Unmounts the HAST pool. Degrades the HAST pool to secondary. This is just an example script which serves as a proof of concept. It does not handle all the possible scenarios and can be extended or altered in any way, for example, to start or stop required services. For this example, a standard UFS file system was used. To reduce the time needed for recovery, a journal-enabled UFS or ZFS file system can be used instead. More detailed information with additional examples can be found at http://wiki.FreeBSD.org/HAST. Troubleshooting HAST should generally work without issues. However, as with any other software product, there may be times when it does not work as supposed. The sources of the problems may be different, but the rule of thumb is to ensure that the time is synchronized between the nodes of the cluster. When troubleshooting HAST, the debugging level of &man.hastd.8; should be increased by starting hastd with -d. This argument may be specified multiple times to further increase the debugging level. Consider also using -F, which starts hastd in the foreground. Recovering from the Split-brain Condition Split-brain occurs when the nodes of the cluster are unable to communicate with each other, and both are configured as primary. This is a dangerous condition because it allows both nodes to make incompatible changes to the data. This problem must be corrected manually by the system administrator. The administrator must decide which node has more important changes or merge them manually. Then, let HAST perform full synchronization of the node which has the broken data. To do this, issue these commands on the node which needs to be resynchronized: &prompt.root; hastctl role init test &prompt.root; hastctl create test &prompt.root; hastctl role secondary test