NAME
sudo, sudoedit - execute a command as another user
SYNOPSIS
sudo -h | -K | -k | -L | -V
sudo -v [-AknS] [-p prompt]
sudo -l[l] [-AknS] [-g groupname|#gid] [-p prompt] [-U username]
[-u username|#uid] [command]
sudo [-AbEHnPS] [-C fd] [-g groupname|#gid] [-p prompt]
[-u username|#uid] [VAR=value] [-i | -s] [command]
sudoedit [-AnS] [-C fd] [-g groupname|#gid] [-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 (15
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 running sudo with the -v option, 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 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 option. 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 option 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
sudoers file.
OPTIONS
sudo accepts the following command line options:
-A Normally, if sudo requires a password, it will read it from
the current terminal. If the -A (askpass) option is
specified, a (possibly graphical) helper program is
executed to read the user's password and output the
password to the standard output. If the SUDO_ASKPASS
environment variable is set, it specifies the path to the
helper program. Otherwise, the value specified by the
askpass option in sudoers(5) is used.
-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.
-C fd Normally, sudo will close all open file descriptors other
than standard input, standard output and standard error.
The -C (close from) option allows the user to specify a
starting point above the standard error (file descriptor
three). Values less than three are not permitted. This
option is only available if the administrator has enabled
the closefrom_override option in sudoers(5).
-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 SUDO_EDITOR, VISUAL or
EDITOR environment variables is run to edit the
temporary files. If none of SUDO_EDITOR, VISUAL or
EDITOR are set, the first 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.
-g group Normally, sudo sets the primary group to the one specified
by the passwd database for the user the command is being
run as (by default, root). The -g (group) option causes
sudo to run the specified command with the primary group
set to group. To specify a gid instead of a group name,
use #gid. When running commands as a gid, many shells
require that the '#' be escaped with a backslash ('\'). If
no -u option is specified, the command will be run as the
invoking user (not root). In either case, the primary
group will be set to group.
-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 [command]
The -i (simulate initial login) option runs the shell
specified in the passwd(5) entry of the target user as a
login shell. This means that login-specific resource files
such as .profile or .login will be read by the shell. If a
command is specified, it is passed to the shell for
execution. Otherwise, an interactive shell is executed.
sudo attempts to change to that user's home directory
before running the shell. It also initializes the
environment, leaving DISPLAY and TERM unchanged, setting
HOME, SHELL, USER, LOGNAME, and PATH, as well as the
contents of /etc/environment on Linux and AIX systems. All
other environment variables are removed.
-K The -K (sure kill) option is like -k except that it removes
the user's timestamp entirely and may not be used in
conjunction with a command or other option. This option
does not require a password.
-k When used by itself, 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.
When used in conjunction with a command or an option that
may require a password, the -k option will cause sudo to
ignore the user's timestamp file. As a result, sudo will
prompt for a password (if one is required by sudoers) and
will not update the user's timestamp 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[l] [command]
If no command is specified, the -l (list) option will list
the allowed (and forbidden) commands for the invoking user
(or the user specified by the -U option) on the current
host. If a command is specified and is permitted by
sudoers, the fully-qualified path to the command is
displayed along with any command line arguments. If
command is specified but not allowed, sudo will exit with a
status value of 1. If the -l option is specified with an l
argument (i.e. -ll), or if -l is specified multiple times,
a longer list format is used.
-n The -n (non-interactive) option prevents sudo from
prompting the user for a password. If a password is
required for the command to run, sudo will display an error
messages and exit.
-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.
-p prompt 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
The prompt specified by the -p option will override the
system password prompt on systems that support PAM unless
the passprompt_override flag is disabled in sudoers.
-S The -S (stdin) option causes sudo to read the password from
the standard input instead of the terminal device. The
password must be followed by a newline character.
-s [command]
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). If a command is specified, it is passed to
the shell for execution. Otherwise, an interactive shell
is executed.
-U user The -U (other user) option is used in conjunction with the
-l option to specify the user whose privileges should be
listed. Only root or a user with sudo ALL on the current
host may use this option.
-u user The -u (user) option causes sudo to run the specified
command as a user other than root. To specify a uid
instead of a user name, 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 15
minutes (or whatever the timeout is set to in sudoers) but
does not run a command.
-- The -- option indicates that sudo should stop processing
command line arguments. It is most useful in conjunction
with the -s option.
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 environment
variables with one important exception. If the setenv option is set in
sudoers, 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 exit status from sudo will
simply be the exit status 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.
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 variables.
If, however, the env_reset option is disabled in sudoers, any variables
not explicitly 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 directory) last when searching for a command in the user's PATH
(if one or both are in the PATH). Note, however, that the PATH
environment variable is further modified in Debian because of the use
of the SECURE_PATH build option.
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 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 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 neither
SUDO_EDITOR nor VISUAL is 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_ASKPASS Specifies the path to a helper program used to read the
password if no terminal is available or if the -A
option is specified.
SUDO_COMMAND Set to the command run by sudo
SUDO_EDITOR Default editor to use in -e (sudoedit) mode
SUDO_GID Set to the group ID of the user who invoked sudo
SUDO_PROMPT Used as the default password prompt
SUDO_PS1 If set, PS1 will be set to its value for the program
being run
SUDO_UID Set to the user ID of the user who invoked sudo
SUDO_USER Set to the login of the user who invoked sudo
USER Set to the target user (root unless the -u option is
specified)
VISUAL Default editor to use in -e (sudoedit) mode if
SUDO_EDITOR is not set
FILES
/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps
/etc/environment Initial environment for -i mode on Linux and
AIX
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 yaz on a machine where the file
system holding ~yaz is not exported as root:
$ sudo -u yaz ls ~yaz
To edit the index.html file as user www:
$ sudo -u www vi ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:
$ sudo -g adm view /var/log/syslog
To run an editor as jim with a different primary group:
$ sudo -u jim -g audio vi ~jim/sound.txt
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)
The file /usr/share/doc/sudo/OPTIONS describes the options used for
building the Debian version of sudo, some of which change default
behaviors documented elsewhere in this document.
AUTHORS
Many people have worked on sudo over the years; this version consists
of code written primarily by:
Todd C. Miller
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 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 particular purpose are disclaimed.
See the LICENSE file distributed with sudo or
http://www.sudo.ws/sudo/license.html for complete details.