sudo
, sudoedit
— execute a command as another user
sudo |
-h | -K |
-k | -L |
-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 sudoers file. See the
COMMAND EXECUTION section below
for more details.
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. If authentication is required,
sudo
will exit if the user's password is not entered
within a configurable time limit. The default password prompt timeout is
5
minutes.
When invoked as sudoedit
, the
-e
option (described below), is implied.
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, the value specified
by the askpass option in sudoers(5) is
used. 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. This option is only available when the administrator has
enabled the
closefrom_override
option in sudoers(5).-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 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).
sudo
will 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 sudoers
file. If the user is authorized by sudoers, the
following steps are taken:
SUDO_EDITOR
, VISUAL
or
EDITOR
environment variables (in that order)
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(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 option sets
the HOME
environment variable to the home
directory of the target user (root by default) as specified by the
password database. The default handling of the
HOME
environment variable depends on
sudoers(5) settings. By default,
sudo
will set HOME
if
env_reset or always_set_home are set,
or if set_home is set and the -s
option is specified on the command line.-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. It also
initializes the environment to a minimal set of variables, similar to what
is present when a user logs in. The
Command environment section
below documents in detail how the -i
option
affects the environment in which a command is run.-K
-K
(sure
kill) option is like -k
except
that it removes the user's time stamp file entirely and may not be used in
conjunction with a command or other option. This option does not require a
password.-k
[command]-k
(kill)
option to sudo
invalidates the user's time stamp
file. 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 time stamp file. As a
result, sudo
will prompt for a password (if one
is required by sudoers) and will not update the user's
time stamp file.
-L
-L
(list
defaults) option will list the parameters that may
be set in a
Defaults
line along with a short description for each. This option will be removed
from a future version of sudo
.-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
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
-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, 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-p
(prompt)
option allows you to override the default password prompt and use a custom
one. The following percent (‘%
’)
escapes are supported:
%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. Only root or a user with the ALL
privilege on the current host may 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
(‘\
’). 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
-V
(version)
option causes sudo
to print its version string and
exit. If the invoking user is already root the -V
option will display the arguments passed to configure when
sudo
was built as well a list of the defaults
sudo
was compiled with as well as the machine's
local network addresses.-v
-v
(validate)
option, sudo
will update the user's time stamp
file, authenticating 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.--
--
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.
sudo
requires that most users authenticate
themselves by default. A password is not required if the invoking user is
root, if the target user is the same as the invoking user, or if the
authentication has been disabled for the user or command in the
sudoers file. Unlike su(1), when
sudo
requires authentication, it validates the
invoking user's credentials, not the target user's (or root's) credentials.
This can be changed via the rootpw,
targetpw and runaspw Defaults entries in
sudoers.
If a user who is not listed in
sudoers tries to run a command via
sudo
, mail is sent to the proper authorities. The
address used for such mail is configurable via the
mailto
sudoers Defaults entry and defaults to
root
.
Note that 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, its value
will be used 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 invoked 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
uses time stamp files
for credential caching. Once a user has been authenticated, the time stamp
is updated and the user may then use sudo without a password for a short
period of time (5
minutes unless overridden by the
timeout option).
By default, sudo
uses a tty-based time stamp which
means that there is a separate time stamp for each of a user's login
sessions. The tty_tickets option can be disabled to force
the use of a single time stamp for all of a user's sessions.
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 via the
syslog and
logfile Defaults settings.
sudo
also supports logging a command's
input and output streams. I/O logging is not on by default but can be
enabled using the log_input and
log_output Defaults flags as well as the
LOG_INPUT
and LOG_OUTPUT
command tags.
Since environment variables can influence program behavior,
sudo
provides a means to restrict which variables
from the user's environment are inherited by the command to be run. There
are two distinct ways sudoers can be configured to handle
with environment variables.
By default, the env_reset option
is enabled. This causes commands to be executed with a new, minimal
environment. On AIX (and Linux systems without PAM), the environment is
initialized with the contents of the
/etc/environment file. On BSD systems, if the
use_loginclass option is enabled, the environment is
initialized based on the path and setenv
settings in /etc/login.conf. The new environment
contains the TERM
, PATH
,
HOME
, MAIL
,
SHELL
, LOGNAME
,
USER
, USERNAME
and
SUDO_*
variables in addition to variables from the
invoking process permitted by the env_check and
env_keep
options. This is effectively a whitelist for environment variables.
If, however, the env_reset option is disabled, 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.
As a special case, if
sudo
's
-i
option (initial login) is specified,
sudo
will initialize the environment regardless of
the value of env_reset. The
DISPLAY
, PATH
and
TERM
variables remain unchanged;
HOME
, MAIL
,
SHELL
, USER
, and
LOGNAME
are set based on the target user. On AIX
(and Linux systems without PAM), the contents of
/etc/environment are also included. On BSD systems,
if the use_loginclass option is enabled, the
path and setenv variables in
/etc/login.conf are also applied. All other
environment variables are removed.
Finally, if the env_file option is defined, any variables present in that file will be set to their specified values as long as they would not conflict with an existing environment variable.
When sudo
executes a command, the
sudoers file specifies the execution envionment 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 sudoers file settings affect the following execution parameters:
See the Command environment section for details on how the environment list is constructed.
If sudo
has been configured with PAM
support or if I/O logging is enabled, sudo
must wait
until the command has completed before it will exit. In the case of PAM,
sudo
must remain running so that it can close the
PAM session when the command is finished. If neither PAM nor I/O logging are
configured, sudo
will execute the command without
calling fork(2). In either case,
sudo
sets up the execution environment as described
above, and calls the execve system call (potentially in a
child process). If I/O logging is enabled, 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.
If the command is run as a child of the
sudo
process (due to PAM or I/O logging),
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 systyem.
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).
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
can log events using either
syslog(3) or a simple log file. In each case the log
format is almost identical.
Commands that sudo runs are logged using the following format (split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; PWD=cwd ; \ USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \ ENV=env_vars COMMAND=command
Where the fields are as follows:
sudo
was run on. This field
is only present when logging via syslog(3).sudo
.sudo
was run on, or “unknown” if
there was no terminal present.sudo
was run
in.Messages are logged using the locale specified
by
sudoers_locale,
which defaults to the “C
” locale.
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:
-n
option was specified but a password was
required.If an error occurs, sudo
will log a
message and, in most cases, send a message to the administrator via email.
Possible errors include:
sudo
encountered an error when parsing the
specified file. In some cases, the actual error may be one line above or
below the line number listed, depending on the type of error.sudo
from running,
but the sudoers file should be checked using
visudo
.sudo
tries to open sudoers using
group permissions to avoid this problem.By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by the syslog daemon, not sudoers itself. As such, they may vary in format on different systems.
On most systems, syslog(3) has a relatively
small log buffer. To prevent the command line arguments from being
truncated, sudo
will split up log messages that are
larger than 960 characters (not including the date, hostname, and the string
“sudo”). When a message is split, additional parts will
include the string “(command continued)” after the user name
and before the continued command line arguments.
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a file, sudoers uses a format similar to syslog(3), with a few important differences:
!
’),
word wrap will be disabled.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.
sudo
will check the ownership of its time
stamp directory (/var/adm/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 time stamp directory
is located in a world-writable directory (e.g.,
/tmp), it is possible for a user to create the time
stamp 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 time stamp dir. This is
unlikely to happen since once the time stamp dir is owned by root and
inaccessible by any other user, the user placing files there would be unable
to get them back out.
sudo
will not honor time stamps set far in
the future. Time stamps 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 time stamp
with a bogus date on systems that allow users to give away files if the time
stamp directory is located in a world-writable directory.
On systems where the boot time is available,
sudo
will ignore time stamps that date from before
the machine booted.
Since time stamp files live in the file system, they can outlive a
user's login session. As a result, a user may be able to login, run a
command with sudo
after authenticating, logout,
login again, and run sudo
without authenticating so
long as the time stamp file's modification time is within
5
minutes (or whatever the timeout is set to in
sudoers). When the tty_tickets
sudoers option is enabled, the time stamp has per-tty
granularity but still may outlive the user's session. On Linux systems where
the devpts filesystem is used, Solaris systems with the devices filesystem,
as well as other systems that utilize a devfs filesystem that monotonically
increase the inode number of devices as they are created (such as Mac OS X),
sudo
is able to determine when a tty-based time
stamp file is stale and will ignore it. Administrators should not rely on
this feature as it is not universally available.
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).
For information on the security implications of sudoers entries, please see the SECURITY NOTES section in sudoers(5).
sudo
utilizes the following environment
variables:
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.-i
mode on AIX and Linux
systemsNote: 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 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"
grep(1), su(1), stat(2), login_cap(3), passwd(5), sudoers(5), 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
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.
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.