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sudo(8)                   BSD System Manager's Manual                  sudo(8)


NAME

     sudo, sudoedit -- execute a command as another user


SYNOPSIS

     sudo -h | -K | -k | -V
     sudo -v [-AknS] [-a type] [-g group] [-h host] [-p prompt] [-u user]
     sudo -l [-AknS] [-a type] [-g group] [-h host] [-p prompt] [-U user]
          [-u user] [command]
     sudo [-AbEHnPS] [-a type] [-C num] [-c class] [-g group] [-h host]
          [-p prompt] [-r role] [-t type] [-u user] [VAR=value] [-i | -s]
          [command]
     sudoedit [-AknS] [-a type] [-C num] [-c class] [-g group] [-h host]
          [-p prompt] [-u user] file ...


DESCRIPTION

     sudo allows a permitted user to execute a command as the superuser or
     another user, as specified by the security policy.  The invoking user's
     real (not effective) user ID is used to determine the user name with
     which to query the security policy.

     sudo supports a plugin architecture for security policies and input/out-
     put logging.  Third parties can develop and distribute their own policy
     and I/O logging plugins to work seamlessly with the sudo front end.  The
     default security policy is sudoers, which is configured via the file
     /opt/local/etc/sudoers, or via LDAP.  See the Plugins section for more
     information.

     The security policy determines what privileges, if any, a user has to run
     sudo.  The policy may require that users authenticate themselves with a
     password or another authentication mechanism.  If authentication is
     required, sudo will exit if the user's password is not entered within a
     configurable time limit.  This limit is policy-specific; the default
     password prompt timeout for the sudoers security policy is unlimited.

     Security policies may support credential caching to allow the user to run
     sudo again for a period of time without requiring authentication.  The
     sudoers policy caches credentials for 5 minutes, unless overridden in
     sudoers(5).  By running sudo with the -v option, a user can update the
     cached credentials without running a command.

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

     Security policies may log successful and failed attempts to use sudo.  If
     an I/O plugin is configured, the running command's input and output may
     be logged as well.

     The options are as follows:

     -A, --askpass
                 Normally, if sudo requires a password, it will read it from
                 the user's terminal.  If the -A (askpass) option is speci-
                 fied, a (possibly graphical) helper program is executed to
                 read the user's password and output the password to the stan-
                 dard output.  If the SUDO_ASKPASS environment variable is
                 set, it specifies the path to the helper program.  Otherwise,
                 if sudo.conf(5) contains a line specifying the askpass pro-
                 gram, that value will be used.  For example:

                     # Path to askpass helper program
                     Path askpass /usr/X11R6/bin/ssh-askpass

                 If no askpass program is available, sudo will exit with an
                 error.

     -b, --background
                 Run the given command in the background.  Note that it is not
                 possible to use shell job control to manipulate background
                 processes started by sudo.  Most interactive commands will
                 fail to work properly in background mode.

     -C num, --close-from=num
                 Close all file descriptors greater than or equal to num
                 before executing a command.  Values less than three are not
                 permitted.  By default, sudo will close all open file
                 descriptors other than standard input, standard output and
                 standard error when executing a command.  The security policy
                 may restrict the user's ability to use this option.  The
                 sudoers policy only permits use of the -C option when the
                 administrator has enabled the closefrom_override option.

     -E, --preserve-env
                 Indicates to the security policy that the user wishes to pre-
                 serve their existing environment variables.  The security
                 policy may return an error if the user does not have permis-
                 sion to preserve the environment.

     -e, --edit  Edit one or more files instead of running a command.  In lieu
                 of a path name, the string "sudoedit" is used when consulting
                 the security policy.  If the user is authorized by the pol-
                 icy, 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 policy is run to edit the
                      temporary files.  The sudoers policy uses the
                      SUDO_EDITOR, VISUAL and EDITOR environment variables (in
                      that order).  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.

                 To help prevent the editing of unauthorized files, the fol-
                 lowing restrictions are enforced unless explicitly allowed by
                 the security policy:

                 o   Symbolic links may not be edited (version 1.8.15 and
                     higher).

                 o   Symbolic links along the path to be edited are not fol-
                     lowed when the parent directory is writable by the invok-
                     ing user unless that user is root (version 1.8.16 and
                     higher).

                 o   Files located in a directory that is writable by the
                     invoking user may not be edited unless that user is root
                     (version 1.8.16 and higher).

                 Users are never allowed to edit device special files.

                 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, --group=group
                 Run the command with the primary group set to group instead
                 of the primary group specified by the target user's password
                 database entry.  The group may be either a group name or a
                 numeric group ID (GID) prefixed with the `#' character (e.g.
                 #0 for GID 0).  When running a command 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.  In either case, the primary group will be set
                 to group.

     -H, --set-home
                 Request that the security policy set the HOME environment
                 variable to the home directory specified by the target user's
                 password database entry.  Depending on the policy, this may
                 be the default behavior.

     -h, --help  Display a short help message to the standard output and exit.

     -h host, --host=host
                 Run the command on the specified host if the security policy
                 plugin supports remote commands.  Note that the sudoers plug-
                 in does not currently support running remote commands.  This
                 may also be used in conjunction with the -l option to list a
                 user's privileges for the remote host.

     -i, --login
                 Run the shell specified by the target user's password data-
                 base entry 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.  The command is run with an environment similar to the
                 one a user would receive at log in.  The Command environment
                 section in the sudoers(5) manual documents how the -i option
                 affects the environment in which a command is run when the
                 sudoers policy is in use.

     -K, --remove-timestamp
                 Similar to the -k option, except that it removes the user's
                 cached credentials entirely and may not be used in conjunc-
                 tion with a command or other option.  This option does not
                 require a password.  Not all security policies support cre-
                 dential caching.

     -k, --reset-timestamp
                 When used without a command, invalidates the user's cached
                 credentials.  In other words, 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 permis-
                 sions from a .logout file.

                 When used in conjunction with a command or an option that may
                 require a password, this option will cause sudo to ignore the
                 user's cached credentials.  As a result, sudo will prompt for
                 a password (if one is required by the security policy) and
                 will not update the user's cached credentials.

                 Not all security policies support credential caching.

     -l, --list  If no command is specified, list the allowed (and forbidden)
                 commands for the invoking user (or the user specified by the
                 -U option) on the current host.  A longer list format is used
                 if this option is specified multiple times and the security
                 policy supports a verbose output format.

                 If a command is specified and is permitted by the security
                 policy, the fully-qualified path to the command is displayed
                 along with any command line arguments.  If command is speci-
                 fied but not allowed, sudo will exit with a status value of
                 1.

     -n, --non-interactive
                 Avoid prompting the user for input of any kind.  If a pass-
                 word is required for the command to run, sudo will display an
                 error message and exit.

     -P, --preserve-groups
                 Preserve the invoking user's group vector unaltered.  By
                 default, the sudoers policy will initialize the group vector
                 to the list of groups the target user is a member of.  The
                 real and effective group IDs, however, are still set to match
                 the target user.

     -p prompt, --prompt=prompt
                 Use a custom password prompt with optional escape sequences.
                 The following percent (`%') escape sequences are supported by
                 the sudoers policy:

                 %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 sin-
                     gle `%' character

                 The custom prompt will override the system password prompt on
                 systems that support PAM unless the passprompt_override flag
                 is disabled in sudoers.

     -S, --stdin
                 Write the prompt to the standard error and read the password
                 from the standard input instead of using the terminal device.
                 The password must be followed by a newline character.

     -s, --shell
                 Run the shell specified by the SHELL environment variable if
                 it is set or the shell specified by the invoking user's pass-
                 word database entry.  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, --other-user=user
                 Used in conjunction with the -l option to list the privileges
                 for user instead of for the invoking user.  The security pol-
                 icy may restrict listing other users' privileges.  The
                 sudoers policy only allows root or a user with the ALL privi-
                 lege on the current host to use this option.

     -u user, --user=user
                 Run the command as a user other than the default target user
                 (usually root).  The user may be either a user name or a
                 numeric user ID (UID) prefixed with the `#' character (e.g.
                 #0 for UID 0).  When running commands as a UID, many shells
                 require that the `#' be escaped with a backslash (`\').  Some
                 security policies may restrict UIDs to those listed in the
                 password database.  The sudoers policy allows UIDs that are
                 not in the password database as long as the targetpw option
                 is not set.  Other security policies may not support this.

     -V, --version
                 Print the sudo version string as well as the version string
                 of the security policy plugin and any I/O plugins.  If the
                 invoking user is already root the -V option will display the
                 arguments passed to configure when sudo was built and plugins
                 may display more verbose information such as default options.

     -v, --validate
                 Update the user's cached credentials, authenticating the user
                 if necessary.  For the sudoers plugin, this extends the sudo
                 timeout for another 5 minutes by default, but does not run a
                 command.  Not all security policies support cached creden-
                 tials.

     --          The -- option indicates that sudo should stop processing com-
                 mand 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 restrictions imposed by the security policy plugin.  The
     sudoers policy subjects variables passed on the command line to the same
     restrictions as normal environment variables with one important excep-
     tion.  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 vari-
     ables that would otherwise be forbidden.  See sudoers(5) for more infor-
     mation.


COMMAND EXECUTION

     When sudo executes a command, the security policy specifies the execution
     environment for the command.  Typically, the real and effective user and
     group and IDs 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).

     The following parameters may be specified by security policy:

     o   real and effective user ID

     o   real and effective group ID

     o   supplementary group IDs

     o   the environment list

     o   current working directory

     o   file creation mode mask (umask)

     o   scheduling priority (aka nice value)

   Process model
     When sudo runs a command, it calls fork(2), sets up the execution envi-
     ronment as described above, and calls the execve system call in the child
     process.  The main sudo process waits until the command has completed,
     then passes the command's exit status to the security policy's close
     function and exits.  If an I/O logging plugin is configured or if the
     security policy explicitly requests it, a new  pseudo-terminal (``pty'')
     is created and a second sudo process is used to relay job control signals
     between the user's existing pty and the new pty the command is being run
     in.  This extra process makes it possible to, for example, suspend and
     resume the command.  Without it, the command would be in what POSIX terms
     an ``orphaned process group'' and it would not receive any job control
     signals.  As a special case, if the policy plugin does not define a close
     function and no pty is required, sudo will execute the command directly
     instead of calling fork(2) first.  The sudoers policy plugin will only
     define a close function when I/O logging is enabled, a pty is required,
     or the pam_session or pam_setcred options are enabled.  Note that
     pam_session and pam_setcred are enabled by default on systems using PAM.

   Signal handling
     When the command is run as a child of the sudo process, sudo will relay
     signals it receives to the command.  The SIGINT and SIGQUIT signals are
     only relayed when the command is being run in a new pty or when the sig-
     nal was sent by a user process, not the kernel.  This prevents the com-
     mand from receiving SIGINT twice each time the user enters control-C.
     Some signals, such as SIGSTOP and SIGKILL, cannot be caught and thus will
     not be relayed to the command.  As a general rule, SIGTSTP should be used
     instead of SIGSTOP when you wish to suspend a command being run by sudo.

     As a special case, sudo will not relay signals that were sent by the com-
     mand it is running.  This prevents the command from accidentally killing
     itself.  On some systems, the reboot(8) command sends SIGTERM to all non-
     system processes other than itself before rebooting the system.  This
     prevents sudo from relaying the SIGTERM signal it received back to
     reboot(8), which might then exit before the system was actually rebooted,
     leaving it in a half-dead state similar to single user mode.  Note, how-
     ever, that this check only applies to the command run by sudo and not any
     other processes that the command may create.  As a result, running a
     script that calls reboot(8) or shutdown(8) via sudo may cause the system
     to end up in this undefined state unless the reboot(8) or shutdown(8) are
     run using the exec() family of functions instead of system() (which
     interposes a shell between the command and the calling process).

     If no I/O logging plugins are loaded and the policy plugin has not
     defined a close() function, set a command timeout or required that the
     command be run in a new pty, sudo may execute the command directly
     instead of running it as a child process.

   Plugins
     Plugins may be specified via Plugin directives in the sudo.conf(5) file.
     They may be loaded as dynamic shared objects (on systems that support
     them), or compiled directly into the sudo binary.  If no sudo.conf(5)
     file is present, or it contains no Plugin lines, sudo will use the tradi-
     tional sudoers security policy and I/O logging.  See the sudo.conf(5)
     manual for details of the /opt/local/etc/sudo.conf file and the
     sudo_plugin(8) manual for more information about the sudo plugin archi-
     tecture.


EXIT VALUE

     Upon successful execution of a command, the exit status from sudo will be
     the exit status of the program that was executed.  If the command termi-
     nated due to receipt of a signal, sudo will send itself the signal that
     terminated the command.

     Otherwise, sudo exits with a value of 1 if there is a configuration/per-
     mission problem or if sudo cannot execute the given command.  In the lat-
     ter 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 to the standard error.  (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 rea-
     son 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.


SECURITY NOTES

     sudo tries to be safe when executing external commands.

     To prevent command spoofing, sudo checks "." and "" (both denoting cur-
     rent 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 envi-
     ronment variable is not modified and is passed unchanged to the program
     that sudo executes.

     Users should never be granted sudo privileges to execute files that are
     writable by the user or that reside in a directory that is writable by
     the user.  If the user can modify or replace the command there is no way
     to limit what additional commands they can run.

     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 inadver-
     tently 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 dis-
     ables core dumps by default while it is executing (they are re-enabled
     for the command that is run).  This historical practice dates from a time
     when most operating systems allowed setuid processes to dump core by
     default.  To aid in debugging sudo crashes, you may wish to re-enable
     core dumps by setting ``disable_coredump'' to false in the sudo.conf(5)
     file as follows:

           Set disable_coredump false

     See the sudo.conf(5) manual for more information.


ENVIRONMENT

     sudo utilizes the following environment variables.  The security policy
     has control over the actual content of the command's environment.

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

     MAIL             Set to the mail spool of the target user when the -i
                      option is specified or when env_reset is enabled in
                      sudoers (unless MAIL is present in the env_keep list).

     HOME             Set to the home directory of the target user when the -i
                      or -H options are specified, when the -s option is spec-
                      ified and set_home is set in sudoers, when
                      always_set_home is enabled in sudoers, or when env_reset
                      is enabled in sudoers and HOME is not present in the
                      env_keep list.

     LOGNAME          Set to the login name of the target user when the -i
                      option is specified, when the set_logname option is
                      enabled in sudoers or when the env_reset option is
                      enabled in sudoers (unless LOGNAME is present in the
                      env_keep list).

     PATH             May be overridden by the security policy.

     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 same value as LOGNAME, described above.

     USERNAME         Same as USER.

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


FILES

     /opt/local/etc/sudo.conf  sudo front end configuration


EXAMPLES

     Note: the following examples assume a properly configured security pol-
     icy.

     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 redi-
     rection work.

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


SEE ALSO

     su(1), stat(2), passwd(5), sudo.conf(5), sudoers(5), sudo_plugin(8),
     sudo(8)


HISTORY

     See the HISTORY file in the sudo distribution (https://www.sudo.ws/his-
     tory.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
     (https://www.sudo.ws/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 pre-
     vent shell escapes with the sudoers(5) plugin's noexec functionality.

     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
     https://bugzilla.sudo.ws/


SUPPORT

     Limited free support is available via the sudo-users mailing list, see
     https://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, includ-
     ing, 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 https://www.sudo.ws/license.html for complete
     details.

Sudo 1.8.16                    January 19, 2016                    Sudo 1.8.16

sudo 1.8.16 - Generated Mon May 16 07:28:22 CDT 2016
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