SUDO(8) BSD System Manager's Manual SUDO(8)NAME
sudo, sudoedit — execute a command as another user
SYNOPSIS
sudo -h | -K | -k | -V
sudo -v [-AknS] [-g group name | #gid] [-p prompt] [-u user name | #uid]
sudo -l[l] [-AknS] [-g group name | #gid] [-p prompt] [-U user name]
[-u user name | #uid] [command]
sudo [-AbEHnPS] [-C fd] [-g group name | #gid] [-p prompt]
[-u user name | #uid] [VAR=value] -i | -s [command]
sudoedit [-AnS] [-C fd] [-g group name | #gid] [-p prompt]
[-u user name | #uid] file ...
DESCRIPTION
sudo allows a permitted user to execute a command as the superuser or
another user, as specified by the security policy.
sudo supports a plugin architecture for security policies and input/out‐
put logging. Third parties can develop and distribute their own policy
and I/O logging plugins to work seamlessly with the sudo front end. The
default security policy is sudoers, which is configured via the file
/etc/sudoers, or via LDAP. See the Plugins section for more information.
The security policy determines what privileges, if any, a user has to run
sudo. The policy may require that users authenticate themselves with a
password or another authentication mechanism. If authentication is
required, sudo will exit if the user's password is not entered within a
configurable time limit. This limit is policy-specific; the default
password prompt timeout for the sudoers security policy is 5 minutes.
Security policies may support credential caching to allow the user to run
sudo again for a period of time without requiring authentication. The
sudoers policy caches credentials for 5 minutes, unless overridden in
sudoers(5). By running sudo with the -v option, a user can update the
cached credentials without running a command.
When invoked as sudoedit, the -e option (described below), is implied.
Security policies may log successful and failed attempts to use sudo. If
an I/O plugin is configured, the running command's input and output may
be logged as well.
The options are as follows:
-A Normally, if sudo requires a password, it will read it from
the user's terminal. If the -A (askpass) option is speci‐
fied, a (possibly graphical) helper program is executed to
read the user's password and output the password to the stan‐
dard output. If the SUDO_ASKPASS environment variable is
set, it specifies the path to the helper program. Otherwise,
if sudo.conf(5) contains a line specifying the askpass pro‐
gram, that value will be used. For example:
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass program is available, sudo will exit with an
error.
-b The -b (background) option tells sudo to run the given com‐
mand in the background. Note that if you use the -b option
you cannot use shell job control to manipulate the process.
Most interactive commands will fail to work properly in back‐
ground mode.
-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). Val‐
ues less than three are not permitted. The security policy
may restrict the user's ability to use the -C option. The
sudoers policy only permits use of the -C option when the
administrator has enabled the closefrom_override option.
-E The -E (preserve environment) option indicates to the secu‐
rity policy that the user wishes to preserve their existing
environment variables. The security policy may return an
error if the -E option is specified and the user does not
have permission to preserve the environment.
-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 security policy. If the user is authorized by the pol‐
icy, 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 policy is run to edit the
temporary files. The sudoers policy uses the
SUDO_EDITOR, VISUAL and EDITOR environment variables (in
that order). If none of SUDO_EDITOR, VISUAL or EDITOR
are set, the first program listed in the editor
sudoers(5) option 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 runs a command with the primary group set to
the one specified by the password database for the user the
command is being run as (by default, root). The -g (group)
option causes sudo to run the command with the primary group
set to group instead. 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 requests that the security policy set
the HOME environment variable to the home directory of the
target user (root by default) as specified by the password
database. Depending on the policy, this may be the default
behavior.
-h The -h (help) option causes sudo to print a short help mes‐
sage to the standard output and exit.
-i [command]
The -i (simulate initial login) option runs the shell speci‐
fied by the password database 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
via the shell's -c option. If no command is specified, an
interactive shell is executed. sudo attempts to change to
that user's home directory before running the shell. The
security policy shall initialize the environment to a minimal
set of variables, similar to what is present when a user logs
in. The Command Environment section in the sudoers(5) manual
documents how the -i option affects the environment in which
a command is run when the sudoers policy is in use.
-K The -K (sure kill) option is like -k except that it removes
the user's cached credentials entirely and may not be used in
conjunction with a command or other option. This option does
not require a password. Not all security policies support
credential caching.
-k [command]
When used alone, the -k (kill) option to sudo invalidates the
user's cached credentials. The next time sudo is run a pass‐
word will be required. This option does not require a pass‐
word and was added to allow a user to revoke sudo permissions
from a .logout file. Not all security policies support cre‐
dential caching.
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 cached credentials. As a result, sudo will prompt
for a password (if one is required by the security policy)
and will not update the user's cached credentials.
-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 the security
policy, the fully-qualified path to the command is displayed
along with any command line arguments. If command is speci‐
fied 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 message and exit.
-P The -P (preserve group vector) option causes sudo to preserve
the invoking user's group vector unaltered. By default, the
sudoers policy 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 by the sudoers policy:
%H expanded to the host name including the domain name (on
if the machine's host name is fully qualified or the fqdn
option is set in sudoers(5))
%h expanded to the local host name without the domain name
%p expanded to the name of the user whose password is being
requested (respects the rootpw, targetpw, and runaspw
flags in sudoers(5))
%U expanded to the login name of the user the command will
be run as (defaults to root unless the -u option is also
specified)
%u expanded to the invoking user's login name
%% two consecutive ‘%’ characters are collapsed into a sin‐
gle ‘%’ character
The prompt specified by the -p option will override the sys‐
tem 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 pass‐
word 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 the password database. If a command is specified, it is
passed to the shell for execution via the shell's -c option.
If no command is specified, 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.
The security policy may restrict listing other users' privi‐
leges. The sudoers policy only allows root or a user with
the ALL privilege on the current host to 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, #uid. When running commands as a uid, many shells
require that the ‘#’ be escaped with a backslash (‘\’).
Security policies may restrict uids to those listed in the
password database. The sudoers policy allows uids that are
not in the password database as long as the targetpw option
is not set. Other security policies may not support this.
-V The -V (version) option causes sudo to print its version
string and the version string of the security policy plugin
and any I/O plugins. If the invoking user is already root
the -V option will display the arguments passed to configure
when sudo was built and plugins may display more verbose
information such as default options.
-v When given the -v (validate) option, sudo will update the
user's cached credentials, authenticating the user's password
if necessary. For the sudoers plugin, this extends the sudo
timeout for another 5 minutes (or whatever the timeout is set
to by the security policy) but does not run a command. Not
all security policies support cached credentials.
-- The -- option indicates that sudo should stop processing com‐
mand line arguments.
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 otherwise be forbidden. See
sudoers(5) for more information.
COMMAND EXECUTION
When sudo executes a command, the security policy specifies the execution
environment for the command. Typically, the real and effective uid and
gid are set to match those of the target user, as specified in the pass‐
word database, and the group vector is initialized based on the group
database (unless the -P option was specified).
The following parameters may be specified by security policy:
· real and effective user ID
· real and effective group ID
· supplementary group IDs
· the environment list
· current working directory
· file creation mode mask (umask)
· scheduling priority (aka nice value)
Process model
When sudo runs a command, it calls fork(2), sets up the execution envi‐
ronment as described above, and calls the execve system call in the child
process. The main sudo process waits until the command has completed,
then passes the command's exit status to the security policy's close
function and exits. If an I/O logging plugin is configured or if the
security policy explicitly requests it, a new pseudo-terminal (“pty”) is
created and a second sudo process is used to relay job control signals
between the user's existing pty and the new pty the command is being run
in. This extra process makes it possible to, for example, suspend and
resume the command. Without it, the command would be in what POSIX terms
an “orphaned process group” and it would not receive any job control sig‐
nals. As a special case, if the policy plugin does not define a close
function and no pty is required, sudo will execute the command directly
instead of calling fork(2) first.
Signal handling
Because the command is run as a child of the sudo process, sudo will
relay signals it receives to the command. Unless the command is being
run in a new pty, the SIGHUP, SIGINT and SIGQUIT signals are not relayed
unless they are sent by a user process, not the kernel. Otherwise, the
command would receive SIGINT twice every time the user entered control-C.
Some signals, such as SIGSTOP and SIGKILL, cannot be caught and thus will
not be relayed to the command. As a general rule, SIGTSTP should be used
instead of SIGSTOP when you wish to suspend a command being run by sudo.
As a special case, sudo will not relay signals that were sent by the com‐
mand it is running. This prevents the command from accidentally killing
itself. On some systems, the reboot(8) command sends SIGTERM to all non-
system processes other than itself before rebooting the system. This
prevents sudo from relaying the SIGTERM signal it received back to
reboot(8), which might then exit before the system was actually rebooted,
leaving it in a half-dead state similar to single user mode. Note, how‐
ever, that this check only applies to the command run by sudo and not any
other processes that the command may create. As a result, running a
script that calls reboot(8) or shutdown(8) via sudo may cause the system
to end up in this undefined state unless the reboot(8) or shutdown(8) are
run using the exec() family of functions instead of system() (which
interposes a shell between the command and the calling process).
If no I/O logging plugins are loaded and the policy plugin has not
defined a close() function, set a command timeout or required that the
command be run in a new pty, sudo may execute the command directly
instead of running it as a child process.
Plugins
Plugins are dynamically loaded based on the contents of the sudo.conf(5)
file. If no sudo.conf(5) file is present, or it contains no Plugin
lines, sudo will use the traditional sudoers security policy and I/O log‐
ging. See the sudo.conf(5) manual for details of the /etc/sudo.conf file
and the sudo_plugin(8) manual for more information about the sudo plugin
architecture.
EXIT VALUE
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 exits with a value of 1 if there is a configuration/per‐
mission problem or if sudo cannot execute the given command. In the lat‐
ter case the error string is printed to the standard error. If sudo can‐
not 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 auto‐
mounter 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.
To prevent command spoofing, sudo checks "." and "" (both denoting cur‐
rent 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 envi‐
ronment variable is not modified and is passed unchanged to the program
that sudo executes.
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 are not subject to sudo's security policy.
The same is true for commands that offer shell escapes (including most
editors). If I/O logging is enabled, subsequent commands will have their
input and/or output logged, but there will not be traditional logs for
those commands. Because of this, care must be taken when giving users
access to commands via sudo to verify that the command does not inadver‐
tently give the user an effective root shell. For more information,
please see the PREVENTING SHELL ESCAPES section in sudoers(5).
To prevent the disclosure of potentially sensitive information, sudo dis‐
ables core dumps by default while it is executing (they are re-enabled
for the command that is run). To aid in debugging sudo crashes, you may
wish to re-enable core dumps by setting “disable_coredump” to false in
the sudo.conf(5) file as follows:
Set disable_coredump false
See the sudo.conf(5) manual for more information.
ENVIRONMENT
sudo utilizes the following environment variables. The security policy
has control over the actual content of the command's environment.
EDITOR Default editor to use in -e (sudoedit) mode if neither
SUDO_EDITOR nor VISUAL is set.
MAIL In -i mode or when env_reset is enabled in sudoers, set
to the mail spool of the target user.
HOME Set to the home directory of the target user if -i or -H
are specified, env_reset or always_set_home are set in
sudoers, or when the -s option is specified and set_home
is set in sudoers.
PATH May be overridden by the security policy.
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 name 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/sudo.conf sudo front end configuration
EXAMPLES
Note: the following examples assume a properly configured security pol‐
icy.
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 shut down 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 redi‐
rection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
SEE ALSOsu(1), stat(2), passwd(5), sudo.conf(5), sudoers(5), sudo_plugin(8),
sudoreplay(8), visudo(8)HISTORY
See the HISTORY file in the sudo distribution
(http://www.sudo.ws/sudo/history.html) for a brief history of sudo.
AUTHORS
Many people have worked on sudo over the years; this version consists of
code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution
(http://www.sudo.ws/sudo/contributors.html) for an exhaustive list of
people who have contributed to 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 pre‐
vent shell escapes with the sudoers(5) plugin's noexec functionality.
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.
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, includ‐
ing, 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 com‐
plete details.
Sudo 1.8.7 March 13, 2013 Sudo 1.8.7
