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Linux 2.6 - man page for sudo (linux section 8)


       sudo, sudoedit - execute a command as another user

       sudo -h | -K | -k | -L | -V

       sudo -v [-AknS] [-g group name|#gid] [-p prompt] [-u username|#uid]

       sudo -l[l] [-AknS] [-g group name|#gid] [-p prompt] [-U user name] [-u user name|#uid]

       sudo [-AbEHnPS] [-C fd] [-g group name|#gid] [-p prompt] [-u user name|#uid] [VAR=value]
       [-i | -s] [command]

       sudoedit [-AnS] [-C fd] [-g group name|#gid] [-p prompt] [-u user name|#uid] file ...

       sudo allows a permitted user to execute a command as the superuser or another user, as
       specified in the sudoers file.  The real and effective uid and gid are set to match those
       of the target user as specified in the passwd file and the group vector is initialized
       based on the group file (unless the -P option was specified).  If the invoking user is
       root or if the target user is the same as the invoking user, no password is required.
       Otherwise, sudo requires that users authenticate themselves with a password by default
       (NOTE: in the default configuration this is the user's password, not the root password).
       Once a user has been authenticated, a time stamp is updated and the user may then use sudo
       without a password for a short period of time (15 minutes unless overridden in sudoers).

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

       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 a
       password is required, sudo will exit if the user's password is not entered within a
       configurable time limit.  The default password prompt timeout is unlimited.

       If a user who is not listed in the sudoers file tries to run a command via sudo, mail is
       sent to the proper authorities, as defined at configure time or in the sudoers file
       (defaults to root).  Note that the 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, sudo will use this
       value 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 being run 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 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 at
       configure time or via the sudoers file.

       sudo accepts the following command line options:

       -A	   Normally, if sudo requires a password, it will read it from the current
		   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.

       -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.

       -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 if the administrator has enabled the closefrom_override option in

       -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).

       -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 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
		       variable 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 sets the primary group to the one specified by the passwd
		   database for the user the command is being run as (by default, root).  The -g
		   (group) option causes sudo to run the specified command with the primary group
		   set to group.  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

       -H	   The -H (HOME) option sets the HOME environment variable to the homedir of the
		   target user (root by default) as specified in passwd(5).  The default handling
		   of the HOME environment variable depends on sudoers(5) settings.  By default,
		   sudo will set HOME if env_reset or always_set_home are set, or if set_home is
		   set and the -s option is specified on the command line.

       -h	   The -h (help) option causes sudo to print a usage message and exit.

       -i [command]
		   The -i (simulate initial login) option runs the shell specified in the
		   passwd(5) 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.
		   Otherwise, an interactive shell is executed.  sudo attempts to change to that
		   user's home directory before running the shell.  It also initializes the
		   environment, leaving DISPLAY and TERM unchanged, setting HOME, MAIL, SHELL,
		   USER, LOGNAME, and PATH, as well as the contents of /etc/environment on Linux
		   and AIX systems.  All other environment variables are removed.

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

       -k	   When used by itself, the -k (kill) option to sudo invalidates the user's time
		   stamp by setting the time on it to the Epoch.  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[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 the -l option is specified with an l
		   argument (i.e. -ll), or 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 messages 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 local host name including the domain name (on if the
		       machine's host name is fully qualified or the fqdn sudoers option is set)

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

		   %p  expanded to the user whose password is being asked for (respects the
		       rootpw, targetpw and runaspw flags in sudoers)

		   %U  expanded to the login name of the user the command will be run as
		       (defaults to root)

		   %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

       -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

       -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 passwd(5).  If a command is
		   specified, it is passed to the shell for execution.	Otherwise, 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
		   sudo ALL 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 the version number and exit.  If
		   the invoking user is already root the -V option will print out a list of the
		   defaults sudo was compiled with as well as the machine's local network

       -v	   If given the -v (validate) option, sudo will update the user's time stamp,
		   prompting for the user's password if necessary.  This extends the sudo timeout
		   for another 15 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

       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
       overwise be forbidden.  See sudoers(5) for more information.

       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 quits with an exit 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 stderr.  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.

       sudo tries to be safe when executing external commands.

       There are two distinct ways to deal with environment variables.	By default, the env_reset
       sudoers option is enabled.  This causes commands to be executed with a minimal environment
       containing TERM, PATH, HOME, SHELL, LOGNAME, USER and USERNAME in addition to variables
       from the invoking process permitted by the env_check and env_keep sudoers options.  There
       is effectively a whitelist for environment variables.

       If, however, the env_reset option is disabled in sudoers, 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.

       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/lib/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 directory writable by anyone (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.  To get
       around this issue you can use a directory that is not world-writable for the time stamps
       (/var/adm/sudo for instance) or create /var/lib/sudo with the appropriate owner (root) and
       permissions (0700) in the system startup files.

       sudo will not honor time stamps set far in the future.  Timestamps 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.

       On systems where the boot time is available, sudo will also not honor time stamps from
       before the machine booted.

       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 15 minutes (or whatever the timeout is set to in sudoers).
       When the tty_tickets option is enabled in sudoers, the time stamp has per-tty granularity
       but still may outlive the user's session.  On Linux systems where the devpts filesystem is
       used, Solaris systems with the devices filesystem, as well as other systems that utilize a
       devfs filesystem that monotonically increase the inode number of devices as they are
       created (such as Mac OS X), sudo is able to determine when a tty-based time stamp file is
       stale and will ignore it.  Administrators should not rely on this feature as it is not
       universally available.

       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 will
       not be logged, nor will sudo's access control affect them.  The same is true for commands
       that offer shell escapes (including most editors).  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).

       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 -i or -H are specified,
		       env_reset or always_set_home are 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 sudoers option is set.

       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 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

       /etc/sudoers	       List of who can run what

       /var/lib/sudo	       Directory containing time stamps

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

       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 shutdown 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"

       grep(1), su(1), stat(2), passwd(5), sudoers(5), visudo(8)

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

	       Todd C. Miller

       See the HISTORY file in the sudo distribution or visit
       http://www.sudo.ws/sudo/history.html for a short history of sudo.

       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.

       If users have sudo ALL there is nothing to prevent them from creating their own program
       that gives them a root shell regardless of any '!' elements in the user specification.

       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).

       If you feel you have found a bug in sudo, please submit a bug report at

       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.

       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.

1.7.4					  July 19, 2010 				  SUDO(8)

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