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 ] [-P ] [-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: 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 (15 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 0 minutes (unless overridden

       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 authorities, 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.



OPTIONS

       sudo accepts the following command line options:



       -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 addresses.



       -l  The -l (list) option will list out the allowed (and forbidden) com­

           mands 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).



       -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 times­

           tamp, 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.



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

           ting the time on it to the epoch.  The next time sudo is run a pass­

           word 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 manipulate the process.



       -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 exist­

           ing 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 con­

           figured 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 sup­

           port 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 environ­

           ment 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.



       -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 conjunction with the -s flag.



RETURN VALUES

       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 configura­

       tion/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 direc­

       tory, the entry is ignored and no error is printed.)  This should not hap­

       pen 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 unreach­

       able.



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, KRBCONFDIR, KRBTKFILE,

       KRB5_CONFIG, LOCALDOMAIN, RES_OPTIONS, HOSTALIASES, NLSPATH,

       PATH_LOCALE, TERMINFO, TERMINFO_DIRS and TERMPATH variables as

       they too can pose a threat.  If the TERMCAP variable is set and is a pathname, 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 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 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 direc­

       tory 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 systems that allow users to give away

       files.



       Please note that sudo will 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 inadver­

       tantly give the user an effective root shell.



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-shell to make the cd and file redi­

       rection 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 or visit

       http://www.sudo.ws/sudo/history.html 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.sudo.ws/sudo/bugs/



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 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.



       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 '!'  ele­

       ments 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

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



April 25, 2002                        1.6.6                               sudo(8)