SUDO(8)

NAME
sudo, sudoedit - execute a command as another user

SYNOPSIS
sudo -h | -K | -k | -L | -V
sudo -v [-AknS] [-a auth_type] [-g group name | #gid] [-p prompt] [-u user name | #uid]
sudo -l [-AknS] [-a auth_type] [-g group name | #gid] [-p prompt] [-U user name] [-u user name | #uid] [command]
sudo [-AbEHnPS] [-a auth_type] [-C fd] [-c class | -] [-g group name | #gid] [-p prompt] [-u user name | #uid] [VAR=value] -i | -s [command]
sudoedit [-AnS] [-a auth_type] [-C fd] [-c class | -] [-g group name | #gid] [-p prompt] [-u user name | #uid] file ...

DESCRIPTION
sudo allows a permitted user to execute a command as the superuser or another user, as specified by the sudoers file. The real and effective uid and gid are set to match those of the target user, as specified in the password database, and the group vector is initialized based on the group database (unless the -P option was specified). See the Command Environment section below for more details.

sudo determines who is an authorized user by consulting the file /etc/sudoers. By running sudo with the -v option, a user can update the time stamp without running a command. If authentication is required, sudo will exit if the user's password is not entered within a configurable time limit. The default password prompt timeout is 5 minutes.

When invoked as sudoedit, the -e option (described below), is implied.

The options are as follows:

-A  Normally, if sudo requires a password, it will read it from the user's terminal. If the -A (askpass) option is specified, a (possibly graphical) helper program is executed to read the user's password and output the password to the standard output. If the SUDO_ASKPASS environment variable is set, it specifies the path to the helper program. Otherwise, the value specified by the askpass option in sudoers(5) is used. If no askpass program is available, sudo will exit with an error.

-a type
    The -a (authentication type) option causes sudo to use the specified authentication type when validating the user, as allowed by /etc/login.conf. The system administrator may specify a list of sudo-specific authentication methods by adding an “auth-sudo” entry in /etc/login.conf. This option is only available on systems that support BSD authentication.

-b  The -b (background) option tells sudo to run the given command in the background. Note that if you use the -b option you cannot use shell job control to manipulate the process. Most interactive commands will fail to work properly in background mode.

-C fd
    Normally, sudo will close all open file descriptors other than standard input, standard output and standard error. The -C (close from) option allows the user to specify a starting point above the standard error (file descriptor three). Values less than three are not permitted. This option is only available when the administrator has enabled the closefrom_override option in sudoers(5).

-c class
    The -c (class) option causes sudo to run the command with resource limits and scheduling priority of the specified login class. The class argument can be either a class name as defined in /etc/login.conf, or a single ‘-’ character. If class is -, the default login class of the target user will be used. Otherwise, the command must be run as the superuser (user ID 0), or sudo must be run from a shell that is already running as the superuser. If the command is being run as a login shell, additional /etc/login.conf settings, such as the umask and environment variables, will be applied, if present. This option is only available on systems with BSD login classes.

-E  The -E (preserve environment) option will override the env_reset option in sudoers(5). It is only available when either the matching command has the SETENV tag or the setenv option is set in sudoers(5). sudo will return an error if the -E option is specified and the user does not have permission to preserve the environment.

-e  The -e (edit) option indicates that, instead of running a command, the user wishes to edit one or more files. In lieu of a command, the string "sudoedit" is used when consulting the sudoers file. If the user is authorized by sudoers, the following steps are taken:

    1.  Temporary copies are made of the files to be edited with the owner set to the invoking user.

    2.  The editor specified by the SUDO_EDITOR, VISUAL or EDITOR environment variables (in that order) is run to edit the temporary files. If none of SUDO_EDITOR, VISUAL or EDITOR are set, the first program listed in the editor sudoers(5) option is used.

    3.  If they have been modified, the temporary files are copied back to their original location and the temporary versions are removed.

    If the specified file does not exist, it will be created. Note that unlike most commands run by sudo, the editor is run with the invoking user's environment unmodified. If, for some reason, sudo is unable to update a file with its edited version, the user will receive a warning and the edited copy will remain in a temporary file.

-g group
    Normally, sudo runs a command with the primary group set to the one specified by the password database for the user the command is being run as (by default, root). The -g (group) option causes sudo to run the command with the primary group set to group instead. To specify a gid instead of a group name, use #gid. When running commands as a gid, many shells require that the ‘#’ be escaped with a backslash (‘\’). If no -u option is specified, the command will be run as the invoking user (not root). In either case, the primary group will be set to group.

-H  The -H (HOME) option option sets the HOME environment variable to the home directory of the target user (root by default) as specified by the password database. The default handling of the HOME environment variable depends on sudoers(5) settings. By default, sudo will not modify HOME (see set_home and always_set_home in sudoers(5)).

-h  The -h (help) option causes sudo to print a short help message to the standard output and exit.

-i [command]
    The -i (simulate initial login) option runs the shell specified by the password database entry of the target user as a login shell. This means that login-specific resource files such as .profile or .login will be read by the shell. If a command is specified, it is passed to the shell for execution via the shell's -c option. If no command is specified, an interactive shell is executed. sudo attempts to change to that user's home directory before running the shell. It also initializes the environment to a minimal set of variables, similar to what is present when a user logs in. The Command Environment section below documents in detail how the -i option affects the environment in which a command is run.

-K  The -K (sure kill) option is like -k except that it removes the user's time stamp file entirely and may not be used in conjunction with a command or other option. This option does not require a password.

-k [command]
    When used alone, the -k (kill) option to sudo invalidates the user's time stamp file. The next time sudo is run a password will be required. This option does not require a password and was added to allow a user to revoke sudo permissions from a .logout file.

    When used in conjunction with a command or an option that may require a password, the -k option will cause sudo to ignore the user's time stamp file. As a result, sudo will prompt for a password (if one is required by sudoers) and will not update the user's time stamp file.

-L  The -L (list defaults) option will list the parameters that may be set in a Defaults line along with a short description for each. This option will be removed from a future version of sudo.

-l [command]
    If no command is specified, the -l (list) option will list the allowed (and forbidden) commands for the invoking user (or the user specified by the -U option) on the current host. If a command is specified and is permitted by sudoers, the fully-qualified path to the command is displayed along with any command line arguments. If command is specified but not allowed, sudo will exit with a status value of 1. If -l is specified multiple times, a longer list format is used.

-n  The -n (non-interactive) option prevents sudo from prompting the user for a password. If a password is required for the command to run, sudo will display an error message and exit.

-P  The -P (preserve group vector) option causes sudo to preserve the invoking user's group vector unaltered. By default, sudo will initialize the group vector to the list of groups the target user is in. The real and effective group IDs, however, are still set to match the target user.

-p prompt
    The -p (prompt) option allows you to override the default password prompt and use a custom one. The following percent (‘%’) escapes are supported:

    %H  expanded to the host name including the domain name (on if the machine's host name is fully qualified or the fqdn option is set in sudoers(5))

    %h  expanded to the local host name without the domain name

    %p  expanded to the name of the user whose password is being requested (respects the rootpw, targetpw, and runaspw flags in sudoers(5))

    %U  expanded to the login name of the user the command will be run as (defaults to root unless the -u option is also specified)

    %u  expanded to the invoking user's login name

    %%  two consecutive ‘%’ characters are collapsed into a single ‘%’ character

    The prompt specified by the -p option will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.

-S  The -S (stdin) option causes sudo to read the password from the standard input instead of the terminal device. The password must be followed by a newline character.

-s [command]
    The -s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in the password database. If a command is specified, it is passed to the shell for execution via the shell's -c option. If no command is specified, an interactive shell is executed.

-U user
    The -U (other user) option is used in conjunction with the -l option to specify the user whose privileges should be listed. Only root or a user with the ALL privilege on the current host may use this option.

-u user
    The -u (user) option causes sudo to run the specified command as a user other than root. To specify a uid instead of a user name, use #uid. When running commands as a uid, many shells require that the ‘#’ be escaped with a backslash (‘\’). Note that if the targetpw Defaults option is set (see sudoers(5)), it is not possible to run commands with a uid not listed in the password database.

-V  The -V (version) option causes sudo to print its version string and exit. If the invoking user is already root the -V option will display the arguments passed to configure when sudo was built as well a list of the defaults sudo was compiled with as well as the machine's local network addresses.

-v  When given the -v (validate) option, sudo will update the user's time stamp file, authenticating the user's password if necessary. This extends the sudo timeout for another 5 minutes (or whatever the timeout is set to in sudoers) but does not run a command.

--  The -- option indicates that sudo should stop processing command line arguments.

Environment variables to be set for the command may also be passed on the command line in the form of VAR=value, e.g. LD_LIBRARY_PATH=/usr/local/pkg/lib. Variables passed on the command line are subject to the same restrictions as normal environment variables with one important exception. If the setenv option is set in sudoers, the command to be run has the SETENV tag set or the command matched is ALL, the user may set variables that would otherwise be forbidden. See sudoers(5) for more information.

  Authentication and Logging
sudo requires that most users authenticate themselves by default. A password is not required if the invoking user is root, if the target user is the same as the invoking user, or if the authentication has been disabled for the user or command in the sudoers file. Unlike su(1), when sudo requires authentication, it validates the invoking user's credentials, not the target user's (or root's) credentials. This can be changed via the rootpw, targetpw and runaspw Defaults entries in sudoers.

If a user who is not listed in sudoers tries to run a command via sudo, mail is sent to the proper authorities. The address used for such mail is configurable via the mailto sudoers Defaults entry and defaults to root.

Note that mail will not be sent if an unauthorized user tries to run sudo with the -l or -v option. This allows users to determine for themselves whether or not they are allowed to use sudo.

If sudo is run by root and the SUDO_USER environment variable is set, its value will be used to determine who the actual user is. This can be used by a user to log commands through sudo even when a root shell has been invoked. It also allows the -e option to remain useful even when invoked via a sudo-run script or program. Note, however, that the sudoers lookup is still done for root, not the user specified by SUDO_USER.

sudo uses time stamp files for credential caching. Once a user has been authenticated, the time stamp is updated and the user may then use sudo without a password for a short period of time ( 5 minutes unless overridden by the timeout option). By default, sudo uses a tty-based time stamp which means that there is a separate time stamp for each of a user's login sessions. The tty_tickets option can be disabled to force the use of a single time stamp for all of a user's sessions.

sudo can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default, sudo will log via syslog(3) but this is changeable via the syslog and logfile Defaults settings.

sudo also supports logging a command's input and output streams. I/O logging is not on by default but can be enabled using the log_input and log_output Defaults flags as well as the LOG_INPUT and LOG_OUTPUT command tags.

  Command Environment
Since environment variables can influence program behavior, sudo provides a means to restrict which variables from the user's environment are inherited by the command to be run. There are two distinct ways sudoers can be configured to handle with environment variables.

By default, the env_reset option is enabled. This causes commands to be executed with a new, minimal environment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of the /etc/environment file. On BSD systems, if the use_loginclass option is enabled, the environment is initialized based on the path and setenv settings in /etc/login.conf. The new environment contains the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER, USERNAME and SUDO_* variables in addition to variables from the invoking process permitted by the env_check and env_keep options. This is effectively a whitelist for environment variables.

If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave like a blacklist. Since it is not possible to blacklist all potentially dangerous environment variables, use of the default env_reset behavior is encouraged.

In all cases, environment variables with a value beginning with () are removed as they could be interpreted as bash functions. The list of environment variables that sudo allows or denies is contained in the output of “sudo -V” when run as root.

Note that the dynamic linker on most operating systems will remove variables that can control dynamic linking from the environment of setuid executables, including sudo. Depending on the operating system this may include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others. These type of variables are removed from the environment before sudo even begins execution and, as such, it is not possible for sudo to preserve them.

As a special case, if sudo's -i option (initial login) is specified, sudo will initialize the environment regardless of the value of env_reset. The DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user. On AIX (and Linux systems without PAM), the contents of /etc/environment are also included. On BSD systems, if the use_loginclass option is enabled, the path and setenv variables in /etc/login.conf are also applied. All other environment variables are removed.

Finally, if the env_file option is defined, any variables present in that file will be set to their specified values as long as they would not conflict with an existing environment variable.

EXIT VALUE
Upon successful execution of a program, the exit status from sudo will simply be the exit status of the program that was executed.

Otherwise, sudo exits with a value of 1 if there is a configuration/permission problem or if sudo cannot execute the given command. In the latter case the error string is printed to the standard error. If sudo cannot stat(2) one or more entries in the user's PATH, an error is printed on stderr. (If the directory does not exist or if it is not really a directory, the entry is ignored and no error is printed.) This should not happen under normal circumstances. The most common reason for stat(2) to return “permission denied” is if you are running an automounter and one of the directories in your PATH is on a machine that is currently unreachable.

LOG FORMAT
sudo can log events using either syslog(3) or a simple log file. In each case the log format is almost identical.

  Accepted command log entries
Commands that sudo runs are logged using the following format (split into multiple lines for readability):

    date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
        USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
        ENV=env_vars COMMAND=command

Where the fields are as follows:

date
    The date the command was run. Typically, this is in the format “MMM, DD, HH:MM:SS”. If logging via syslog(3), the actual date format is controlled by the syslog daemon. If logging to a file and the log_year option is enabled, the date will also include the year.

hostname
    The name of the host sudo was run on. This field is only present when logging via syslog(3).

progname
    The name of the program, usually sudo or sudoedit. This field is only present when logging via syslog(3).

username
    The login name of the user who ran sudo.

ttyname
    The short name of the terminal (e.g. “console”, “tty01”, or “pts/0”) sudo was run on, or “unknown” if there was no terminal present.

cwd The current working directory that sudo was run in.

runasuser
    The user the command was run as.

runasgroup
    The group the command was run as if one was specified on the command line.

logid
    An I/O log identifier that can be used to replay the command's output. This is only present when the log_input or log_output option is enabled.

env_vars
    A list of environment variables specified on the command line, if specified.

command
    The actual command that was executed.

Messages are logged using the locale specified by sudoers_locale, which defaults to the “C” locale.

  Denied command log entries
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:

user NOT in sudoers
    The user is not listed in the sudoers file.

user NOT authorized on host
    The user is listed in the sudoers file but is not allowed to run commands on the host.

command not allowed
    The user is listed in the sudoers file for the host but they are not allowed to run the specified command.

3 incorrect password attempts
    The user failed to enter their password after 3 tries. The actual number of tries will vary based on the number of failed attempts and the value of the passwd_tries sudoers option.

a password is required
    The -n option was specified but a password was required.

sorry, you are not allowed to set the following environment variables
    The user specified environment variables on the command line that were not allowed by sudoers.

  Error log entries
If an error occurs, sudo will log a message and, in most cases, send a message to the administrator via email. Possible errors include:

parse error in /etc/sudoers near line N
    sudo encountered an error when parsing the specified file. In some cases, the actual error may be one line above or below the line number listed, depending on the type of error.

problem with defaults entries
    The sudoers file contains one or more unknown Defaults settings. This does not prevent sudo from running, but the sudoers file should be checked using visudo.

timestamp owner (username): such user
    The time stamp directory owner, as specified by the timestampowner setting, could not be found in the password database.

unable to open/read /etc/sudoers
    The sudoers file could not be opened for reading. This can happen when the sudoers file is located on a remote file system that maps user ID 0 to a different value. Normally, sudo tries to open sudoers using group permissions to avoid this problem.

unable to stat /etc/sudoers
    The /etc/sudoers file is missing.

/etc/sudoers is not a regular file
    The /etc/sudoers file exists but is not a regular file or symbolic link.

/etc/sudoers is owned by uid N, should be 0
    The sudoers file has the wrong owner.

/etc/sudoers is world writable
    The permissions on the sudoers file allow all users to write to it. The sudoers file must not be world-writable, the default file mode is 0440 (readable by owner and group, writable by none).

/etc/sudoers is owned by gid N, should be 1
    The sudoers file has the wrong group ownership.

unable to open /var/run/sudo/username/ttyname
    sudoers was unable to read or create the user's time stamp file.

unable to write to /var/run/sudo/username/ttyname
    sudoers was unable to write to the user's time stamp file.

unable to mkdir to /var/run/sudo/username
    sudoers was unable to create the user's time stamp directory.

  Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by the syslog daemon, not sudoers itself. As such, they may vary in format on different systems.

On most systems, syslog(3) has a relatively small log buffer. To prevent the command line arguments from being truncated, sudo will split up log messages that are larger than 960 characters (not including the date, hostname, and the string “sudo”). When a message is split, additional parts will include the string “(command continued)” after the user name and before the continued command line arguments.

  Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a file, sudoers uses a format similar to syslog(3), with a few important differences:

1.  The progname and hostname fields are not present.

2.  If the log_year sudoers option is enabled, the date will also include the year.

3.  Lines that are longer than loglinelen characters (80 by default) are word-wrapped and continued on the next line with a four character indent. This makes entries easier to read for a human being, but makes it more difficult to use grep(1) on the log files. If the loglinelen sudoers option is set to 0 (or negated with a ‘’!), word wrap will be disabled.

SECURITY NOTES
sudo tries to be safe when executing external commands.

To prevent command spoofing, sudo checks "." and "" (both denoting current directory) last when searching for a command in the user's PATH (if one or both are in the PATH). Note, however, that the actual PATH environment variable is not modified and is passed unchanged to the program that sudo executes.

sudo will check the ownership of its time stamp directory ( /var/run/sudo by default) and ignore the directory's contents if it is not owned by root or if it is writable by a user other than root. On systems that allow non-root users to give away files via chown(2), if the time stamp directory is located in a world-writable directory (e.g., /tmp), it is possible for a user to create the time stamp directory before sudo is run. However, because sudo checks the ownership and mode of the directory and its contents, the only damage that can be done is to “hide” files by putting them in the time stamp dir. This is unlikely to happen since once the time stamp dir is owned by root and inaccessible by any other user, the user placing files there would be unable to get them back out.

sudo will not honor time stamps set far in the future. Time stamps with a date greater than current_time + 2 * TIMEOUT will be ignored and sudo will log and complain. This is done to keep a user from creating his/her own time stamp with a bogus date on systems that allow users to give away files if the time stamp directory is located in a world-writable directory.

Since time stamp files live in the file system, they can outlive a user's login session. As a result, a user may be able to login, run a command with sudo after authenticating, logout, login again, and run sudo without authenticating so long as the time stamp file's modification time is within 5 minutes (or whatever the timeout is set to in sudoers). When the tty_tickets sudoers option is enabled, the time stamp has per-tty granularity but still may outlive the user's session.

Please note that sudo will normally only log the command it explicitly runs. If a user runs a command such as sudo su or sudo sh, subsequent commands run from that shell are not subject to sudo's security policy. The same is true for commands that offer shell escapes (including most editors). If I/O logging is enabled, subsequent commands will have their input and/or output logged, but there will not be traditional logs for those commands. Because of this, care must be taken when giving users access to commands via sudo to verify that the command does not inadvertently give the user an effective root shell. For more information, please see the PREVENTING SHELL ESCAPES section in sudoers(5).

To prevent the disclosure of potentially sensitive information, sudo disables core dumps by default while it is executing (they are re-enabled for the command that is run).

For information on the security implications of sudoers entries, please see the SECURITY NOTES section in sudoers(5).

ENVIRONMENT
sudo utilizes the following environment variables:

EDITOR
    Default editor to use in -e (sudoedit) mode if neither SUDO_EDITOR nor VISUAL is set.

MAIL
    In -i mode or when env_reset is enabled in sudoers, set to the mail spool of the target user.

HOME
    Set to the home directory of the target user if -H it specified, always_set_home is set in sudoers, or when the -s option is specified and set_home is set in sudoers.

PATH
    Set to a sane value if the secure_path option is set in the sudoers file.

SHELL
    Used to determine shell to run with -s option.

SUDO_ASKPASS
    Specifies the path to a helper program used to read the password if no terminal is available or if the -A option is specified.

SUDO_COMMAND
    Set to the command run by sudo.

SUDO_EDITOR
    Default editor to use in -e (sudoedit) mode.

SUDO_GID
    Set to the group ID of the user who invoked sudo.

SUDO_PROMPT
    Used as the default password prompt.

SUDO_PS1
    If set, PS1 will be set to its value for the program being run.

SUDO_UID
    Set to the user ID of the user who invoked sudo.

SUDO_USER
    Set to the login name of the user who invoked sudo.

USER
    Set to the target user (root unless the -u option is specified).

VISUAL
    Default editor to use in -e (sudoedit) mode if SUDO_EDITOR is not set.

FILES

/etc/sudoers
    List of who can run what

/var/run/sudo
    Directory containing time stamps

/etc/environment
    Initial environment for -i mode on AIX and Linux systems

EXAMPLES
Note: the following examples assume suitable sudoers(5) entries.

To get a file listing of an unreadable directory:

    $ sudo ls /usr/local/protected

To list the home directory of user yaz on a machine where the file system holding ~yaz is not exported as root:

    $ sudo -u yaz ls ~yaz

To edit the index.html file as user www:

    $ sudo -u www vi ~www/htdocs/index.html

To view system logs only accessible to root and users in the adm group:

    $ sudo -g adm view /var/log/syslog

To run an editor as jim with a different primary group:

    $ sudo -u jim -g audio vi ~jim/sound.txt

To shut down a machine:

    $ sudo shutdown -r +15 "quick reboot"

To make a usage listing of the directories in the /home partition. Note that this runs the commands in a sub-shell to make the cd and file redirection work.

    $ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

SEE ALSO
grep(1), su(1), stat(2), login_cap(3), passwd(5), sudoers(5), sudoreplay(8), visudo(8)

HISTORY
See the HISTORY file in the sudo distribution (http://www.sudo.ws/sudo/history.html) for a brief history of sudo.

AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by:

Todd C. Miller

See the CONTRIBUTORS file in the sudo distribution (http://www.sudo.ws/sudo/contributors.html) for an exhaustive list of people who have contributed to sudo.

CAVEATS
There is no easy way to prevent a user from gaining a root shell if that user is allowed to run arbitrary commands via sudo. Also, many programs (such as editors) allow the user to run commands via shell escapes, thus avoiding sudo's checks. However, on most systems it is possible to prevent shell escapes with sudo's noexec functionality. See the sudoers(5) manual for details.

It is not meaningful to run the cd command directly via sudo, e.g.,

    $ sudo cd /usr/local/protected

since when the command exits the parent process (your shell) will still be the same. Please see the EXAMPLES section for more information.

Running shell scripts via sudo can expose the same kernel bugs that make setuid shell scripts unsafe on some operating systems (if your OS has a /dev/fd/ directory, setuid shell scripts are generally safe).

BUGS
If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/

SUPPORT
Limited free support is available via the sudo-users mailing list, see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.

DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with sudo or http://www.sudo.ws/sudo/license.html for complete details.