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SUDO(8) MAINTENANCE COMMANDS SUDO(8)
NAME
sudo, sudoedit - execute a command as another user
SYNOPSIS
sudo -h | -K | -k | -L | -l | -V | -v
sudo [-bEHPS] [-p prompt] [-u username|#uid] [VAR=value] {-i | -s | command}
sudoedit [-S] [-p prompt] [-u username|#uid] file ...
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 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 them-
selves 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 com-
mand. 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 unau-
thorized 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 speci-
fied by SUDO_USER.
sudo can log both successful and unsuccessful attempts (as well as errors) to sys-
log(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:
-b The -b (background) option tells sudo to run the given command in the back-
ground. Note that if you use the -b option you cannot use shell job control to
manipulate the process.
-E The -E (preserve environment) option will override the env_reset option in
sudoers(5)). It is only available when either the matching command has the
SETENV tag or the setenv option is set in sudoers(5).
-e The -e (edit) option indicates that, instead of running a command, the user
wishes to edit one or more files. In lieu of a command, the string "sudoedit"
is used when consulting the sudoers file. If the user is authorized by sudoers
the following steps are taken:
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 environ-
ment 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.
-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 (see set_home and always_set_home in sudoers(5)).
-h The -h (help) option causes sudo to print a usage message and exit.
-i The -i (simulate initial login) option runs the shell specified in the
passwd(5) entry of the user that the command is being run as. The command name
argument given to the shell begins with a '-' to tell the shell to run as a
login shell. sudo attempts to change to that user's home directory before run-
ning the shell. It also initializes the environment, leaving TERM unchanged,
setting HOME, SHELL, USER, LOGNAME, and PATH, and unsetting all other environ-
ment variables. Note that because the shell to use is determined before the
sudoers file is parsed, a runas_default setting in sudoers will specify the
user to run the shell as but will not affect which shell is actually run.
-K The -K (sure kill) option is like -k except that it removes the user's times-
tamp entirely. Like -k, this option does not require a password.
-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.
-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).
-l The -l (list) option will list out the allowed (and forbidden) commands for the
invoking user on the current host.
-P The -P (preserve group vector) option causes sudo to preserve the invoking
user's group vector unaltered. By default, sudo will initialize the group vec-
tor 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.
-p The -p (prompt) option allows you to override the default password prompt and
use a custom one. The following percent ('%') escapes are supported:
%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 set)
%h expanded to the local hostname without the domain name
%p expanded to the user whose password is being asked for (respects the
rootpw, targetpw and runaspw flags in sudoers)
%U expanded to the login name of the user the command will be run as (defaults
to root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into a single % character
-S The -S (stdin) option causes sudo to read the password from the standard input
instead of the terminal device.
-s The -s (shell) option runs the shell specified by the SHELL environment vari-
able if it is set or the shell as specified in passwd(5).
-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. When running
commands as a uid, many shells require that the '#' be escaped with a backslash
('\'). Note that if the targetpw Defaults option is set (see sudoers(5)) it is
not possible to run commands with a uid not listed in the password database.
-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.
-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
for another 5 minutes (or whatever the timeout is set to in sudoers) but does
not run a command.
-- The -- flag indicates that sudo should stop processing command line arguments.
It is most useful in conjunction with the -s flag.
Environment variables to be set for the command may also be passed on the command
line in the form of VAR=value, e.g. LD_LIBRARY_PATH=/usr/local/pkg/lib. Variables
passed on the command line are subject to the same restrictions as normal environ-
ment variables with one important exception. If the setenv option is set in sudo-
ers, the command to be run has the SETENV tag set or the command matched is ALL,
the user may set variables that would overwise be forbidden. See sudoers(5) for
more information.
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 configuration/permis-
sion 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.
There are two distinct ways to deal with environment variables. By default, the
env_reset sudoers option is enabled. This causes commands to be executed with a
minimal environment containing TERM, PATH, HOME, SHELL, LOGNAME, USER and USERNAME
in addition to variables from the invoking process permitted by the env_check and
env_keep sudoers options. There is effectively a whitelist for environment vari-
ables.
If, however, the env_reset option is disabled in sudoers, any variables not explic-
itly denied by the env_check and env_delete options are inherited from the invoking
process. In this case, env_check and env_delete behave like a blacklist. Since it
is not possible to blacklist all potentially dangerous environment variables, use
of the default env_reset behavior is encouraged.
In all cases, environment variables with a value beginning with () are removed as
they could be interpreted as bash functions. The list of environment variables
that sudo allows or denies is contained in the output of sudo -V when run as root.
Note that the dynamic linker on most operating systems will remove variables that
can control dynamic linking from the environment of setuid executables, including
sudo. Depending on the operating system this may include _RLD*, DYLD_*, LD_*,
LDR_*, LIBPATH, SHLIB_PATH, and others. These type of variables are removed from
the environment before sudo even begins execution and, as such, it is not possible
for sudo to preserve them.
To prevent command spoofing, sudo checks "." and "" (both denoting current direc-
tory) 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 modi-
fied and is passed unchanged to the program that sudo executes.
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 or if it is writable
by a user other than 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 any-
one (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 com-
plain. 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 normally 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. For
more information, please see the PREVENTING SHELL ESCAPES section in sudoers(5).
ENVIRONMENT
sudo utilizes the following environment variables:
EDITOR Default editor to use in -e (sudoedit) mode if VISUAL is not set
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
PATH Set to a sane value if the secure_path sudoers option is set.
SHELL Used to determine shell to run with -s option
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
USER Set to the target user (root unless the -u option is specified)
VISUAL Default editor to use in -e (sudoedit) mode
FILES
/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps
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 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"
SEE ALSO
grep(1), su(1), stat(2), passwd(5), sudoers(5), visudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists of code writ-
ten primarily by:
Todd C. Miller
Chris Jepeway
See the HISTORY file in the sudo distribution or visit http://www.sudo.ws/sudo/his-
tory.html for a short history of sudo.
CAVEATS
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 the 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).
BUGS
If you feel you have found a bug in sudo, please submit a bug report at
http://www.sudo.ws/sudo/bugs/
SUPPORT
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.
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 partic-
ular purpose are disclaimed. See the LICENSE file distributed with sudo or
http://www.sudo.ws/sudo/license.html for complete details.
1.6.9p17 Jun 21, 2008 SUDO(8)
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