sudo
, sudoedit
— execute a command as another user
sudo |
-h | -K |
-k | -V |
sudo |
-v [-AknS ]
[-a auth_type]
[-g group name | #gid]
[-p prompt]
[-u user name | #uid] |
sudo |
-l [l]
[-AknS ]
[-a auth_type]
[-g group name | #gid]
[-p prompt]
[-U user name]
[-u user name | #uid]
[command] |
sudo |
[-AbEHnPS ]
[-a auth_type]
[-C fd]
[-c class | -]
[-g group name | #gid]
[-p prompt]
[-r role]
[-t type]
[-u user name | #uid]
[VAR=value]
-i | -s
[command] |
sudoedit |
[-AnS ]
[-a auth_type]
[-C fd]
[-c class | -]
[-g group name | #gid]
[-p prompt]
[-u user name | #uid]
file ... |
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/output 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
sudo
requires a password, it will
read it from the user's 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, if
sudo.conf(5) contains a line specifying the askpass
program, 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.
-a
type-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
systems that support BSD authentication.-b
-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. Most interactive
commands will fail to work properly in background mode.-C
fdsudo
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. 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.-c
class-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 capabilities 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.-E
-E
(preserve environment)
option indicates to the security 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
-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 policy, the following steps are taken:
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.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
groupsudo
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
-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
-h
(help)
option causes sudo
to print a short help message
to the standard output and exit.-i
[command]-i
(simulate
initial login) option runs the shell specified 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
-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]-k
(kill)
option to sudo
invalidates the user's cached
credentials. 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. Not all security policies support
credential 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]-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 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
-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
-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-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
%h
%p
%U
-u
option is also
specified)%u
%%
%
’ characters
are collapsed into a single ‘%
’
characterThe 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.
-r
role-r
(role)
option causes the new (SELinux) security context to have the role
specified by role.-S
-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]-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.-t
type-t
(type)
option causes the new (SELinux) security context to have the type
specified by type. If no type is specified, the
default type is derived from the specified role.-U
user-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'
privileges. The sudoers policy only allows root or a
user with the ALL
privilege on the current host to
use this option.-u
user-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
-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
-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.--
--
option indicates that
sudo
should stop processing command 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.
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 password 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:
When sudo
runs a command, it calls
fork(2), sets up the execution environment 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 signals. 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.
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 command 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, however, 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 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 logging. 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.
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/permission problem or if
sudo
cannot execute the given command. In the latter
case the error string is printed to the standard error. 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.
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.
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
inadvertently 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
disables 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.
sudo
utilizes the following environment
variables. The security policy has control over the actual content of the
command's environment.
EDITOR
-e
(sudoedit) mode if
neither SUDO_EDITOR
nor
VISUAL
is set.MAIL
-i
mode or when env_reset is
enabled in sudoers, set to the mail spool of the target
user.HOME
-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
SHELL
-s
option.SUDO_ASKPASS
-A
option is
specified.SUDO_COMMAND
SUDO_EDITOR
-e
(sudoedit) mode.SUDO_GID
SUDO_PROMPT
SUDO_PS1
PS1
will be set to its value for the
program being run.SUDO_UID
SUDO_USER
USER
-u
option
is specified).VISUAL
-e
(sudoedit) mode if
SUDO_EDITOR
is not set.sudo
front end configurationNote: the following examples assume a properly configured security policy.
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 redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
su(1), stat(2), login_cap(3), passwd(5), sudo.conf(5), sudoers(5), sudo_plugin(8), sudoreplay(8), visudo(8)
See the HISTORY file in the sudo
distribution (https://www.sudo.ws/sudo/history.html) for a brief history of
sudo.
Many people have worked on sudo
over the
years; this version consists of code written primarily by:
See the CONTRIBUTORS file in the sudo
distribution (https://www.sudo.ws/sudo/contributors.html) for an exhaustive
list of people who have contributed to 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 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).
If you feel you have found a bug in sudo
,
please submit a bug report at https://www.sudo.ws/sudo/bugs/
Limited free support is available via the sudo-users mailing list, see https://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 https://www.sudo.ws/sudo/license.html for
complete details.