


sudo(8)                MAINTENANCE COMMANDS               sudo(8)


NAME
       sudo - execute a command as another user

SYNOPSIS
       sudo -V | -h | -l | -L | -v | -k | -K | -s | [ -H ] [-S ]
       [ -b ] | [ -p prompt ] [ -c class|- ] [ -a auth_type ] [
       -u username/#uid ] command

DESCRIPTION
       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
       (the group vector is also initialized when the target user
       is not root).  By default, sudo requires that users
       authenticate themselves with a password (NOTE: this is the
       user's password, not the root password).  Once a user has
       been authenticated, a timestamp is updated and the user
       may then use sudo without a password for a short period of
       time (five minutes by default).

       sudo determines who is an authorized user by consulting
       the file /etc/sudoers.  By giving sudo the -v flag a user
       can update the time stamp without running a command.  The
       password prompt itself will also time out if the user's
       password is not entered with N minutes (again, this is
       defined at configure time and defaults to 5 minutes).

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

       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.

OPTIONS
       sudo accepts the following command line options:

       -V  The -V (version) option causes sudo to print the
           version number and exit.

       -l  The -l (list) option will list out the allowed (and
           forbidden) commands for the user on the current host.

       -L  The -L (list defaults) option will list out the
           parameters that may be set in a Defaults line along
           with a short description for each.  This option is
           useful in conjunction with grep(1).



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sudo(8)                MAINTENANCE COMMANDS               sudo(8)


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

       -v  If given the -v (validate) option, sudo will update
           the user's timestamp, prompting for the user's
           password if necessary.  This extends the sudo timeout
           to for another N minutes (where N is defined at
           installation time and defaults to 5 minutes) but does
           not run a command.

       -k  The -k (kill) option to sudo invalidates the user's
           timestamp 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.

       -K  The -K (sure kill) option to sudo removes the user's
           timestamp entirely.  This option does not require a
           password.

       -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 command.

       -p  The -p (prompt) option allows you to override the
           default password prompt and use a custom one.  If the
           password prompt contains the %u escape, %u will be
           replaced with the user's login name.  Similarly, %h
           will be replaced with the local hostname.

       -c  The -c (class) option causes sudo to run the specified
           command with resources limited by the specified login
           class.  The class argument can be either a class name
           as defined in /etc/login.conf, or a single '-'
           character.  Specifying a class of - indicates that the
           command should be run restricted by the default login
           capabilities for the user the command is run as.  If
           the class argument specifies an existing user class,
           the command must be run as root, or the sudo command
           must be run from a shell that is already root.  This
           option is only available on systems with BSD login
           classes where sudo has been configured with the
           --with-logincap option.

       -a  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 where sudo has
           been configured with the --with-bsdauth option.



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sudo(8)                MAINTENANCE COMMANDS               sudo(8)


       -u  The -u (user) option causes sudo to run the specified
           command as a user other than root.  To specify a uid
           instead of a username, use "#uid".

       -s  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).

       -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).  By default, sudo
           does not modify HOME.

       -S  The -S (stdin) option causes sudo to read the password
           from standard input instead of the terminal device.

       --  The -- flag indicates that sudo should stop processing
           command line arguments.  It is most useful in
           conjunction with the -s flag.

RETURN VALUES
       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.

SECURITY NOTES
       sudo tries to be safe when executing external commands.
       Variables that control how dynamic loading and binding is
       done can be used to subvert the program that sudo runs.
       To combat this the LD_*, _RLD_*, SHLIB_PATH (HP-UX only),
       and LIBPATH (AIX only) environment variables are removed
       from the environment passed on to all commands executed.
       sudo will also remove the IFS, ENV, BASH_ENV, KRB_CONF,
       KRB5_CONFIG, LOCALDOMAIN, RES_OPTIONS and HOSTALIASES
       variables as they too can pose a threat.

       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.

       For security reasons, if your OS supports shared libraries
       and does not disable user-defined library search paths for



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sudo(8)                MAINTENANCE COMMANDS               sudo(8)


       setuid programs (most do), you should either use a linker
       option that disables this behavior or link sudo
       statically.

       sudo will check the ownership of its timestamp directory
       (/var/run/sudo by default) and ignore the directory's
       contents if it is not owned by root and only writable by
       root.  On systems that allow non-root users to give away
       files via chown(2), if the timestamp directory is located
       in a directory writable by anyone (e.g.: /tmp), it is
       possible for a user to create the timestamp 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 timestamp dir.  This is unlikely to happen
       since once the timestamp 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 timestamps (/var/adm/sudo for instance)
       or create /var/run/sudo with the appropriate owner (root)
       and permissions (0700) in the system startup files.

       sudo will not honor timestamps 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
       timestamp with a bogus date on system that allow users to
       give away files.

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 yazza on a machine
       where the filesystem holding ~yazza is not exported as
       root:

        % sudo -u yazza ls ~yazza

       To edit the index.html file as user www:

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

       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-



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       shell to make the cd and file redirection work.

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


ENVIRONMENT
       sudo utilizes the following environment variables:

        PATH                   Set to a sane value if SECURE_PATH is set
        SHELL                  Used to determine shell to run with -s option
        USER                   Set to the target user (root unless the -u option
                               is specified)
        HOME                   In -s or -H mode (or if sudo was configured with
                               the --enable-shell-sets-home option), set to
                               homedir of the target user.
        SUDO_PROMPT            Used as the default password prompt
        SUDO_COMMAND           Set to the command run by sudo
        SUDO_USER              Set to the login of the user who invoked sudo
        SUDO_UID               Set to the uid of the user who invoked sudo
        SUDO_GID               Set to the gid of the user who invoked sudo
        SUDO_PS1               If set, PS1 will be set to its value


FILES
        /etc/sudoers           List of who can run what
        /var/run/sudo              Directory containing timestamps


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

               Todd Miller
               Chris Jepeway

       See the HISTORY file in the sudo distribution for a short
       history of sudo.

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

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 for complete details.

CAVEATS
       There is no easy way to prevent a user from gaining a root
       shell if that user has access to commands allowing shell
       escapes.




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sudo(8)                MAINTENANCE COMMANDS               sudo(8)


       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 supports the /dev/fd/
       directory, setuid shell scripts are generally safe).

SEE ALSO
       sudoers(5), visudo(8), su(1).













































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