Sudo Manual
NAME
sudo
, sudoedit
— execute a command as another
user
SYNOPSIS
sudo |
-h | -K |
-k | -V |
sudo |
-v [-AknS ]
[-a type]
[-g group]
[-h host]
[-p prompt]
[-u user] |
sudo |
-l [-AknS ]
[-a type]
[-g group]
[-h host]
[-p prompt]
[-U user]
[-u user]
[command] |
sudo |
[-AbEHnPS ] [-a
type] [-C
num] [-c
class] [-g
group] [-h
host] [-p
prompt] [-r
role] [-t
type] [-u
user]
[VAR=value]
[-i | -s ]
[command] |
sudoedit |
[-AknS ] [-a
type] [-C
num] [-c
class] [-g
group] [-h
host] [-p
prompt] [-u
user] 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/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
,--askpass
- Normally, if
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 theSUDO_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,--auth-type
=type- Use the specified BSD authentication type when validating the user, if 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
,--background
- Run the given command in the background. Note that it is not possible to
use shell job control to manipulate background processes started by
sudo
. Most interactive commands will fail to work properly in background mode. -C
num,--close-from
=num- Close all file descriptors greater than or equal to
num before executing a command. Values less than
three are not permitted. By default,
sudo
will close all open file descriptors other than standard input, standard output and standard error when executing a command. The security policy may restrict the user's ability to use this option. The sudoers policy only permits use of the-C
option when the administrator has enabled the closefrom_override option. -c
class,--login-class
=class- Run the command with resource limits and scheduling priority of the
specified login class. The
class argument can be either a class name as defined
in /etc/login.conf, or a single
‘
-
’ character. If class is-
, the default login class of the target user will be used. Otherwise, the command must be run as the superuser (user ID 0), orsudo
must be run from a shell that is already running as the superuser. If the command is being run as a login shell, additional /etc/login.conf settings, such as the umask and environment variables, will be applied, if present. This option is only available on systems with BSD login classes. -E
,--preserve-env
- Indicates to the security policy that the user wishes to preserve their existing environment variables. The security policy may return an error if the user does not have permission to preserve the environment.
-e
,--edit
- Edit one or more files instead of running a command. In lieu of a path
name, the string "sudoedit" is used when consulting the security
policy. If the user is authorized by the policy, the following steps are
taken:
- Temporary copies are made of the files to be edited with the owner set to the invoking user.
- The editor specified by the policy is run to edit the
temporary files. The sudoers policy uses the
SUDO_EDITOR
,VISUAL
andEDITOR
environment variables (in that order). If none ofSUDO_EDITOR
,VISUAL
orEDITOR
are set, the first program listed in the editor sudoers(5) option is used. - 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,--group
=group- Run the command with the primary group set to group
instead of the primary group specified by the target user's password
database entry. The group may be either a group name
or a numeric group ID (GID) prefixed with the
‘
#
’ character (e.g.#0
for GID 0). When running a command 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. In either case, the primary group will be set to group. -H
,--set-home
- Request that the security policy set the
HOME
environment variable to the home directory specified by the target user's password database entry. Depending on the policy, this may be the default behavior. -h
,--help
- Display a short help message to the standard output and exit.
-h
host,--host
=host- Run the command on the specified host if the
security policy plugin supports remote commands. Note that the
sudoers plugin does not currently support running remote
commands. This may also be used in conjunction with the
-l
option to list a user's privileges for the remote host. -i
,--login
- Run the shell specified by the target user's password database entry 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 command is run with an environment similar to the one a user would receive at log 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
,--remove-timestamp
- Similar to the
-k
option, 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
,--reset-timestamp
- When used without a command, invalidates the user's cached credentials. In
other words, 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 revokesudo
permissions from a .logout file.When used in conjunction with a command or an option that may require a password, this 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.Not all security policies support credential caching.
-l
,--list
- If no command is specified, list the allowed (and
forbidden) commands for the invoking user (or the user specified by the
-U
option) on the current host. A longer list format is used if this option is specified multiple times and the security policy supports a verbose output format.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. -n
,--non-interactive
- Avoid prompting the user for input of any kind. If a password is required
for the command to run,
sudo
will display an error message and exit. -P
,--preserve-groups
- 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 a member of. The real and effective group IDs, however, are still set to match the target user.
-p
prompt,--prompt
=prompt- Use a custom password prompt with optional escape sequences. The following
percent (‘
%
’) escape sequences 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 single ‘%
’ character
The custom prompt will override the system password prompt on systems that support PAM unless the passprompt_override flag is disabled in sudoers.
-r
role,--role
=role- Run the command with an SELinux security context that includes the specified role.
-S
,--stdin
- Write the prompt to the standard error and read the password from the standard input instead of using the terminal device. The password must be followed by a newline character.
-s
,--shell
- Run the shell specified by the
SHELL
environment variable if it is set or the shell specified by the invoking user's password database entry. 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,--type
=type- Run the command with an SELinux security context that includes the specified type. If no type is specified, the default type is derived from the role.
-U
user,--other-user
=user- Used in conjunction with the
-l
option to list the privileges for user instead of for the invoking user. The security policy may restrict listing other users' privileges. The sudoers policy only allows root or a user with theALL
privilege on the current host to use this option. -u
user,--user
=user- Run the command as a user other than the default target user (usually
root ).
The user may be either a user name or a numeric user
ID (UID) prefixed with the ‘
#
’ character (e.g.#0
for UID 0). When running commands as a UID, many shells require that the ‘#
’ be escaped with a backslash (‘\
’). Some 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
,--version
- Print the
sudo
version string as well as 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 whensudo
was built and plugins may display more verbose information such as default options. -v
,--validate
- Update the user's cached credentials, authenticating the user if
necessary. For the sudoers plugin, this extends the
sudo
timeout for another5
minutes by default, but does not run a command. Not all security policies support cached credentials. --
- The
--
option indicates thatsudo
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 restrictions imposed by
the security policy plugin. The sudoers policy subjects
variables passed on the command line 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 user and group and IDs 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:
- real and effective user ID
- real and effective group ID
- supplementary group IDs
- the environment list
- current working directory
- file creation mode mask (umask)
- SELinux role and type
- Solaris project
- Solaris privileges
- BSD login class
- scheduling priority (aka nice value)
Process model
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. The sudoers policy plugin will only define a close
function when I/O logging is enabled, a pty is required, or the
pam_session or pam_setcred options are
enabled. Note that pam_session and
pam_setcred are enabled by default on systems using
PAM.
Signal handling
When 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
Plugins may be specified via Plugin
directives in the sudo.conf(5) file. They may be loaded as dynamic shared objects (on
systems that support them), or compiled directly into the
sudo
binary. 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.
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/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.
SECURITY NOTES
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.
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 neitherSUDO_EDITOR
norVISUAL
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 ifSUDO_EDITOR
is not set.
FILES
- /etc/sudo.conf
sudo
front end configuration
EXAMPLES
Note: 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"
SEE ALSO
su(1), stat(2), login_cap(3), 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:
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 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).
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.