diff --git a/en_US.ISO8859-1/books/handbook/basics/chapter.xml b/en_US.ISO8859-1/books/handbook/basics/chapter.xml index dfa2d22d5a..8cfa367f3a 100644 --- a/en_US.ISO8859-1/books/handbook/basics/chapter.xml +++ b/en_US.ISO8859-1/books/handbook/basics/chapter.xml @@ -1,3646 +1,3645 @@ 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. User names must be - unique on the system as no two users can have the same + 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 user account should have an associated - password. While the password can be blank, this is - highly discouraged. + 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 of 65535 or lower as higher UIDs may cause compatibility issues with software that does not support integers larger than 32-bits. 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, &os; does not force users to change - their passwords periodically. Password expiration can - be enforced on a per-user basis using &man.pw.8;, + 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 a space, 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 become gain superuser + 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 Table 4.1, followed by some examples of their usage. Refer to 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 + superuser. The &man.adduser.8; utility is interactive and walks through the steps for creating a new user account. As seen - in Example 4.2, either input the required information or + 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, which is required to provide the account with superuser access. 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 exists from the editor, the 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 Example 4.4, the superuser has typed + 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 Example - 4.5. + 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: &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 &man.pw.8; is a command line utility to 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, spawn multiple - processes and other intermediate preprocessors. + 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 in order to limit network - communications. + 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 list and do not replace the list of existing + 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 Code Meaning ad ATAPI (IDE) disk da SCSI direct access disk acd ATAPI (IDE) CDROM cd SCSI CDROM fd Floppy disk
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: 72257; load averages: 0.13, 0.09, 0.03 up 0+13:38:33 22:39:10 47 processes: 1 running, 46 sleeping CPU states: 12.6% user, 0.0% nice, 7.8% system, 0.0% interrupt, 79.7% idle Mem: 36M Active, 5256K Inact, 13M Wired, 6312K Cache, 15M Buf, 408K Free Swap: 256M Total, 38M Used, 217M Free, 15% Inuse 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 system has been formatted with the ZFS file system, the ARC line provides an indication of 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;. 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/users/Makefile b/en_US.ISO8859-1/books/handbook/users/Makefile deleted file mode 100644 index b44bd80628..0000000000 --- a/en_US.ISO8859-1/books/handbook/users/Makefile +++ /dev/null @@ -1,15 +0,0 @@ -# -# Build the Handbook with just the content from this chapter. -# -# $FreeBSD$ -# - -CHAPTERS= users/chapter.xml - -VPATH= .. - -MASTERDOC= ${.CURDIR}/../${DOC}.${DOCBOOKSUFFIX} - -DOC_PREFIX?= ${.CURDIR}/../../../.. - -.include "../Makefile" diff --git a/en_US.ISO8859-1/books/handbook/users/chapter.xml b/en_US.ISO8859-1/books/handbook/users/chapter.xml deleted file mode 100644 index 03f2dcca59..0000000000 --- a/en_US.ISO8859-1/books/handbook/users/chapter.xml +++ /dev/null @@ -1,1026 +0,0 @@ - - - - Users and Basic Account Management - - NeilBlakey-MilnerContributed by - - - - - - - - Synopsis - - &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, every - user must have a user account. - - After reading this chapter, you will know: - - - - The differences between the various user accounts on a - &os; system. - - - - How to add and remove user accounts. - - - - How to change account details, such as the user's full - name or preferred shell. - - - - How to set limits on a per-account basis to control the - resources, such as memory and CPU time, that accounts and - groups of accounts are allowed to access. - - - - How to use groups to make account management - easier. - - - - Before reading this chapter, you should: - - - - Understand the basics of &unix; - and &os;. - - - - - - Introduction - - Since all access to the &os; system is achieved via accounts - and all processes are run by users, user and account management - is important. - - Every account on a &os; system has certain information - associated with it to identify the account. - - - - User name - - - The user name is typed at the login: - prompt. User names must be unique on the system as no two - users can have the same user name. There are a number of - rules for creating valid user names, documented in - &man.passwd.5;. Typically user names consist of eight or - fewer all lower case characters in order to maintain - backwards compatibility with applications. - - - - - Password - - - Each account has an associated password. While the - password can be blank, this is highly discouraged and - every account should have a password. - - - - - User ID (UID) - - - The User ID (UID) is a number, - traditionally from 0 to 65535 - It is possible to use - UIDs/GIDs as - large as 4294967295, but such IDs can cause serious - problems with software that makes assumptions about - the values of IDs. - , used to uniquely identify the user to the - system. Internally, &os; uses the - UID to identify users. Commands that - allow a user name to be specified will first convert it to - the UID. Though unlikely, it is - possible for several accounts with different user names to - share the same UID. As far as &os; is - concerned, these accounts are one user. - - - - - Group ID (GID) - - - The Group ID (GID) is a number, - traditionally from 0 to 65535, 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. A user may also be a - member of more than one group. - - - - - Login class - - - Login classes are an extension to the group mechanism - that provide additional flexibility when tailoring the - system to different users. - - - - - Password change time - - - By default &os; does not force users to change their - passwords periodically. Password expiration can be - enforced 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. 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. - This information can be associated with the - account. - - - - - 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 default environment users use - to interact 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. - - - - - There are three main types of accounts: the superuser, system accounts, and user accounts. The superuser - account, usually called root, is used to - manage the system with no limitations on privileges. System - accounts are used to run services. User accounts are - assigned to real people and are used to log in and use the - system. - - - The Superuser Account - - - accounts - superuser (root) - - The superuser account, usually called - root, is used to perform system - administration tasks and should not be used for day-to-day - tasks like sending and receiving mail, general exploration of - the system, or programming. - - This is because the superuser, unlike normal user - accounts, can operate without limits, and misuse of the - superuser account may result in spectacular disasters. User - accounts are unable to destroy the system by mistake, so it is - generally best to use normal user accounts whenever possible, - unless extra privilege is required. - - Always double and triple-check any commands issued as the - superuser, since an extra space or missing character can mean - irreparable data loss. - - Always create a user account for the system administrator - and use this account to log in to the system for general - usage. This applies equally to multi-user or single-user - systems. Later sections will discuss how to create additional - accounts and how to change between the normal user and - superuser. - - - - 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 the primary means of access for real - people to the system. User accounts insulate the user and - the environment, preventing users from damaging the system - or other users, and allowing users to customize their - environment without affecting others. - - Every person accessing the system should have a unique - user account. This allows the administrator to find out who - is doing what, prevents users from clobbering each others' - settings or reading each others' mail, and so forth. - - Each user can set up their own environment to accommodate - their use of the system, by using alternate shells, editors, - key bindings, and language. - - - - - Modifying Accounts - - - accounts - modifying - - - &os; provides a variety of different commands to manage - user accounts. The most common commands are summarized below, - followed by more detailed examples of their usage. - - - - - - - - - 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 simple 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 - &man.adduser.8; is a simple program for adding new users - 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. - - - 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 use - &man.rmuser.8;. 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. - - - - 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 -Updating password file, updating databases, done. -Updating group file: trusted (removing group jru -- personal group is empty) done. -Removing user's incoming mail file /var/mail/jru: done. -Removing files belonging to jru from /tmp: done. -Removing files belonging to jru from /var/tmp: done. -Removing files belonging to jru from /var/tmp/vi.recover: done. -&prompt.root; - - - - - <command>chpass</command> - - chpass - &man.chpass.1; can be used to change user database - information such as passwords, shells, and personal - information. - - Only the superuser can change other users' information and - passwords with &man.chpass.1;. - - When passed no options, aside from an optional username, - &man.chpass.1; displays an editor containing user information. - When the user exists from the editor, the user database is - updated with the new information. - - - You will be asked for your password after exiting the - editor if you are not the superuser. - - - - Interactive <command>chpass</command> by - 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: - - - A user can change only a small subset of this - information, and only for their own user account. - - - Interactive <command>chpass</command> by Normal - 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: - - - - &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;. NIS support is - automatic, so specifying the yp before - the command is not necessary. How to configure NIS is - covered in . - - - - <command>passwd</command> - - passwd - - accounts - changing password - - &man.passwd.1; is the usual way to change your own - password as a user, or another user's password as the - superuser. - - - To prevent accidental or unauthorized changes, the user - must enter their original password before a new password can - be set. This is not the case when the superuser changes a - user's password. - - - - Changing Your Password - - &prompt.user; passwd -Changing local password for jru. -Old password: -New password: -Retype new password: -passwd: updating the database... -passwd: done - - - - 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 - - &man.pw.8; is a command line utility to 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 filecoredumpsize generated by a - program is subordinate to other limitslimiting userscoredumpsize 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 CPUcputimelimiting userscputime 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 filefilesizelimiting usersfilesize 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 processesmaxproclimiting usersmaxproc 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, spawn multiple processes and other intermediate - preprocessors. - - - - - memorylocked - - - The maximum amount of memorymemorylockedlimiting usersmemorylocked 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 memorymemoryuselimiting usersmemoryuse 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 openopenfileslimiting usersopenfiles. - 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 mbufssbsizelimiting userssbsize, a user may consume in order to limit network - communications. - - - - - stacksize - - - The maximum size of a process stackstacksizelimiting usersstacksize. 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;. - - - - 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 list and do not replace the list of 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;. - - - - Becoming Superuser - - There are several ways to do things as the superuser. The - worst way is to log in as root directly. - Usually very little activity requires root - so logging off and logging in as root, - performing tasks, then logging off and on again as a normal user - is a waste of time. - - A better way is to use &man.su.1; without providing a login - but using - to inherit the root environment. - Not providing a login will imply super user. For this to work - the login that must be in the wheel group. - An example of a typical software installation would involve the - administrator unpacking the software as a normal user and then - elevating their privileges for the build and installation of - the software. - - - 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; - - - Note in this example the transition to - root is less painful than logging off - and back on twice. - - Using &man.su.1; works well for single systems or small - networks with just one system administrator. For more complex - environments (or even for these simple environments) - sudo should be used. It is provided as a port, - security/sudo. It allows for - things like activity logging, granting users the ability to only - run certain commands as the superuser, and several other - options. - -