OpenBSD manual page server

Manual Page Search Parameters

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

       sudo - execute a command as another user

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

       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: by default
       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 (5 minutes unless overridden in sudoers).

       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 within 5 minutes (unless overrid-
       den via sudoers).

       If a user who is not listed in the sudoers file tries to
       run a command via sudo, mail is sent to the proper author-
       ities, as defined at configure time or 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 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 or via the sudoers file.

       sudo accepts the following command line options:

       -V  The -V (version) option causes sudo to print the ver-
           sion 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 addresses.

       -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

1.6.7                     March 13, 2003                        1

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

           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).

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

       -v  If given the -v (validate) option, sudo will update
           the user's timestamp, prompting for the user's pass-
           word 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.

       -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.  Likewise, 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 manipu-
           late the process.

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

           %u      expanded to the invoking user's login name

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

           %h      expanded to the local hostname without the
                   domain name

           %H      expanded to the local hostname including the
                   domain name (on if the machine's hostname is
                   fully qualified or the fqdn sudoers option is

           %%      two consecutive % characters are collaped into
                   a single % character

       -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 '-' charac-
           ter.  Specifying a class of - indicates that the

1.6.7                     March 13, 2003                        2

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

           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.

       -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 vari-
           able to the homedir of the target user (root by
           default) as specified in passwd(5).  By default, sudo
           does not modify HOME.

       -P  The -P (preserve group vector) option causes sudo to
           preserve the 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.

       -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 conjunc-
           tion with the -s flag.

       Upon successful execution of a program, the return value
       from sudo will simply be the return value 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 exe-
       cute the given command.  In the latter case the error
       string is printed to stderr.  If sudo cannot stat(2) one

1.6.7                     March 13, 2003                        3

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

       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 circum-
       stances.  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.
       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,
       TERMINFO_DIRS and TERMPATH variables as they too can pose
       a threat.  If the TERMCAP variable is set and is a path-
       name, it too is ignored.  Additionally, if the LC_* or
       LANGUAGE variables contain the / or % characters, they are
       ignored.  If sudo has been compiled with SecurID support,
       the VAR_ACE, USR_ACE and DLC_ACE variables are cleared as
       well.  The list of environment variables that sudo clears
       is contained in the output of sudo -V when run as root.

       To prevent command spoofing, sudo checks "." and "" (both
       denoting current directory) last when searching for a com-
       mand 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
       setuid programs (most do), you should either use a linker
       option that disables this behavior or link sudo stati-

       sudo will check the ownership of its timestamp directory
       (/var/run/sudo by default) and ignore the directory's con-
       tents 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 pos-
       sible 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 dam-
       age 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

1.6.7                     March 13, 2003                        4

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

       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 systems that allow users to
       give away files.

       Please note that sudo will only log the command it explic-
       itly 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.

       Note: the following examples assume suitable sudoers(5)

       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

        % 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-
       shell to make the cd and file redirection work.

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

       sudo utilizes the following environment variables:

1.6.7                     March 13, 2003                        5

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

        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

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

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

               Todd Miller
               Chris Jepeway

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

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

       Sudo is provided ``AS IS'' and any express or implied war-
       ranties, including, but not limited to, the implied war-
       ranties of merchantability and fitness for a particular
       purpose are disclaimed.  See the LICENSE file distributed
       with sudo for complete details.

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

       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 specifi-

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

1.6.7                     March 13, 2003                        6

SUDO(8)                MAINTENANCE COMMANDS               SUDO(8)

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

1.6.7                     March 13, 2003                        7