sudo, sudoedit - execute a command as another user
sudo -K | -L | -V | -h | -k | -l | -v
sudo [-HPSb] [-a auth_type] [-c class|-] [-p prompt] [-u username|#uid] {-e file [...] | -i | -s | command}
sudoedit [-S] [-a auth_type] [-p prompt] [-u username|#uid] file [...]
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 and the group vector is initialized based on the group file (unless the -P option was specified). If the invoking user is root or if the target user is the same as the invoking user, no password is required. Otherwise, sudo requires that users authenticate themselves with a password by default (NOTE: in the default configuration 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).
When invoked as sudoedit, the -e option (described below), is implied.
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 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 in 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.
If sudo is run by root and the SUDO_USER environment variable is set, sudo will use this value to determine who the actual user is. This can be used by a user to log commands through sudo even when a root shell has been invoked. It also allows the -e flag to remain useful even when being run via a sudo-run script or program. Note however, that the sudoers lookup is still done for root, not the user specified by SUDO_USER.
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 sudo_ers file.
sudo accepts the following command line options:
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 VISUAL or EDITOR environment variables is run to edit the temporary files. If neither VISUAL nor EDITOR are set, the program listed in the editor sudoers variable is used.
3. If they have been modified, the temporary files are copied back to their original location and the temporary versions are removed.
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.
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 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.
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, CDPATH, 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. Environment variables with a value beginning with () are also removed as they could be interpreted as bash functions. 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 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 worldwritable 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 inadvertently give the user an effective root shell.
sudo utilizes the following environment variables:
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 file system 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 redirection work.
$ sudo sh -c “cd /home ; du -s * | sort -rn > USAGE"
grep(1) , su(1) , stat(2) , login_cap(3) , sudoers(5) , passwd(5) , visudo(8)
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.
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 prevent shell escapes with sudo’s noexec functionality. See the sudoers(5) manual for details.
It is not meaningful to run the cd command directly via sudo, e.g.
$ sudo cd /usr/local/protected
since when whe command exits the parent process (your shell) will still be the same. Please see the EXAMPLES section for more information.
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 has a /dev/fd/ directory, setuid shell scripts are generally safe).
If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/
Commercial support is available for sudo, see http://www.sudo.ws/sudo/support.html for details.
Limited free support is available via the sudo-users mailing list, see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
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 or
http://www.sudo.ws/sudo/license.html for complete details.