SUDO(8) MAINTENANCE COMMANDS SUDO(8)NAME
sudo, sudoedit - execute a command as another user
SYNOPSIS
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 [...]
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 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 pass-
word 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 vari-
able 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
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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 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:
-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)).
-K The -K (sure kill) option is like -k except that it
removes the user's timestamp entirely. Like -k, this
option does not require a password.
-L The -L (list defaults) option will list out the parame-
ters that may be set in a Defaults line along with a
short description for each. This option is useful in
conjunction with grep(1).
-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 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 the standard input instead of the terminal device.
-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.
-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 sys-
tems that support BSD authentication where sudo has been
configured with the --with-bsdauth option.
-b The -b (background) option tells sudo to run the given
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command in the background. Note that if you use the -b
option you cannot use shell job control to manipulate
the process.
-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 capabili-
ties 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.
-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 tem-
porary 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.
-h The -h (help) option causes sudo to print a usage mes-
sage 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
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user's home directory before running the shell. It also
initializes the environment, leaving TERM unchanged,
setting HOME, SHELL, USER, LOGNAME, and PATH, and unset-
ting all other environment 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 (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) option will list out the allowed (and for-
bidden) commands for the user on the current host.
-p The -p (prompt) option allows you to override the
default password prompt and use a custom one. The fol-
lowing percent (`%') escapes are supported:
%u expanded to the invoking user's login name
%U expanded to the login name of the user the com-
mand 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
set)
%% two consecutive % characters are collapsed into
a single % character
-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).
-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. Note that if the tar-
getpw Defaults option is set (see sudoers(5)) it is not
possible to run commands with a uid not listed in the
password database.
-v If given the -v (validate) option, sudo will update the
user's timestamp, prompting for the user's password if
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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 conjunc-
tion 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
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.
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, 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 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.
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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 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 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. Times-
tamps 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 expli-
citly 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 (includ-
ing 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.
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 sudo was configured with
the --with-secure-path option
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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 par-
tition. 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 ALSOgrep(1), su(1), stat(2), login_cap(3), sudoers(5),
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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.
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 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).
BUGS
If you feel you have found a bug in sudo, please submit a
bug report at http://www.sudo.ws/sudo/bugs/
SUPPORT
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.
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SUDO(8) MAINTENANCE COMMANDS SUDO(8)DISCLAIMER
Sudo is provided ``AS IS'' and any express or implied war-
ranties, including, but not limited to, the implied warran-
ties 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.
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