1.5.7 NAME sudo - execute a command as the superuser SYNOPSIS sudo -V | -h | -l | -v | -k | -s | -H | [ -b ] | [ -p prompt ] [ -u username/#uid] command DESCRIPTION sudo allows a permitted user to execute a command as the superuser (real and effective uid and gid are set to 0 and root's group as set in the passwd file respectively). 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 password is not entered with N minutes (again, this is defined at installation time and defaults to 5 minutes). If an unauthorized user executes sudo, mail will be sent from the user to the local authorities (defined at installation time). sudo was designed to log via the 4.3 BSD syslog(3) facility but can log to a file instead if so desired (or to both syslog and a file). 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. -h The -h (help) option causes sudo to print the version of sudo and a usage message before exiting. -v If given the -v (validate) option, sudo will update the user's timestamp file, prompting for a 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 removes the user's timestamp file, thus requiring a password the next time sudo is run. This option does not require a password and was added to allow a user to revoke sudo permissions from a .logout file. -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 - 1 - Formatted: January 21, 1999 sudo(8) 5/Nov/98 sudo(8) MAINTENANCE COMMANDS MAINTENANCE COMMANDS 1.5.7 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 by the user's login name. Similarly, %h will be replaced by the local hostname. -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). -- 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 via perror(3). If sudo cannot stat(2) one or more entries in the user's PATH the error is printed on stderr via perror(3). (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(3) 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_*, SHLIB_PATH (HP-UX only), LIBPATH (AIX only), and _RLD_* environment variables are removed from the environment passed on to all commands executed. sudo will also remove the IFS, ENV, BASH_ENV and KRB_CONF 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 - 2 - Formatted: January 21, 1999 sudo(8) 5/Nov/98 sudo(8) MAINTENANCE COMMANDS MAINTENANCE COMMANDS 1.5.7 the program that sudo executes. For security reasons, if your OS supports shared libraries, sudo should always be statically linked unless the dynamic loader disables user-defined library search paths for setuid programs. (Most modern dynamic loaders do this.) sudo will check the ownership of its timestamp directory (/var/run/sudo or /tmp/.odus by default) and ignore the directory's contents if it is not owned by root and only read, writable, and executable by root. On systems that allow users to give files away to root (via chown), if the timestamp directory is located in a directory writable by anyone (ie: /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, 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). sudo will not honor timestamp files set far in the future. Timestamp files with a date greater than current_time + 2 * TIMEOUT will be ignored and sudo will log the anomaly. This is done to keep a user from creating his/her own timestamp file with a bogus date. FILES /etc/sudoers file of authorized users. 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 mode, set to homedir of root (or runas user) if built with the SHELL_SETS_HOME option SUDO_PROMPT Replaces 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 AUTHORS Many people have worked on sudo over the years, this version consists of code written primarily by: - 3 - Formatted: January 21, 1999 sudo(8) 5/Nov/98 sudo(8) MAINTENANCE COMMANDS MAINTENANCE COMMANDS 1.5.7 Jeff Nieusma David Hieb Todd Miller Chris Jepeway See the HISTORY file in the sudo distribution for more details. Please send all bugs, comments, and changes to sudo- bugs@courtesan.com. DISCLAIMER This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. CAVEATS There is no easy way to prevent a user from gaining a root shell if that user has access to commands allow 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 '!' 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. SEE ALSO sudoers(5), visudo(8), su(1). - 4 - Formatted: January 21, 1999 sudo(8) 5/Nov/98 sudo(8) MAINTENANCE COMMANDS MAINTENANCE COMMANDS 1.5.7 - 5 - Formatted: January 21, 1999