sudo - execute a command as another user
sudo -h | -K | -k | -V sudo -v [-AknS] [-g group] [-h host] [-p prompt] [-u user] sudo -l [-AknS] [-g group] [-h host] [-p prompt] [-U user] [-u user] [command] sudo [-AbEHnPS] [-C num] [-g group] [-h host] [-p prompt] [-u user] [VAR=value] [-i | -s] [command] sudoedit [-AknS] [-C num] [-g group] [-h host] [-p prompt] [-u user] file ...
SUDO(8) 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] [-h host] [-p prompt] [-u user]
sudo -l [-AknS] [-g group] [-h host] [-p prompt] [-U user] [-u user]
[command]
sudo [-AbEHnPS] [-C num] [-g group] [-h host] [-p prompt] [-u user]
[VAR=value] [-i | -s] [command]
sudoedit [-AknS] [-C num] [-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. The invoking user's
real (not effective) user ID is used to determine the user name with
which to query 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(4). 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 the SUDO_ASKPASS
environment variable is set, it specifies the path to the
helper program. Otherwise, if sudo.conf(4) 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), or
sudo 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:
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(4) 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.
To help prevent the editing of unauthorized files, the
following restrictions are enforced unless explicitly
allowed by the security policy:
o Symbolic links may not be edited
(version 1.8.15 and higher).
o Symbolic links along the path to be
edited are not followed when the parent
directory is writable by the invoking
user unless that user is root (version
1.8.16 and higher).
o Files located in a directory that is
writable by the invoking user may not
be edited unless that user is root
(version 1.8.16 and higher).
Users are never allowed to edit device special files.
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(4)
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 revoke sudo
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(4))
%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(4))
%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 the ALL 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 when sudo 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 another 5 minutes by default, but does
not run a command. Not all security policies support
cached credentials.
-- The -- 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 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(4) 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:
o real and effective user ID
o real and effective group ID
o supplementary group IDs
o the environment list
o current working directory
o file creation mode mask (umask)
o SELinux role and type
o Solaris project
o Solaris privileges
o BSD login class
o 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. The SIGINT and SIGQUIT signals are
only relayed when the command is being run in a new pty or when the
signal was sent by a user process, not the kernel. This prevents the
command from receiving SIGINT twice each time the user enters 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(1m) 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(1m), 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(1m) or
shutdown(1m) via sudo may cause the system to end up in this undefined
state unless the reboot(1m) or shutdown(1m) 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(4)
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(4) 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(4) manual for details of the /etc/sudo.conf file and the
sudo_plugin(1m) manual for more information about the sudo plugin
architecture.
EXIT VALUE
Upon successful execution of a command, the exit status from sudo will
be the exit status of the program that was executed. If the command
terminated due to receipt of a signal, sudo will send itself the signal
that terminated the command.
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 to the standard error. (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.
Users should never be granted sudo privileges to execute files that are
writable by the user or that reside in a directory that is writable by
the user. If the user can modify or replace the command there is no
way to limit what additional commands they can run.
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(4).
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). This historical practice dates
from a time when most operating systems allowed setuid processes to
dump core by default. To aid in debugging sudo crashes, you may wish
to re-enable core dumps by setting disable_coredump to false in the
sudo.conf(4) file as follows:
Set disable_coredump false
See the sudo.conf(4) 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 Set to the mail spool of the target user when the -i
option is specified or when env_reset is enabled in
sudoers (unless MAIL is present in the env_keep list).
HOME Set to the home directory of the target user when the
-i or -H options are specified, when the -s option is
specified and set_home is set in sudoers, when
always_set_home is enabled in sudoers, or when
env_reset is enabled in sudoers and HOME is not
present in the env_keep list.
LOGNAME Set to the login name of the target user when the -i
option is specified, when the set_logname option is
enabled in sudoers or when the env_reset option is
enabled in sudoers (unless LOGNAME is present in the
env_keep list).
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 same value as LOGNAME, described above.
USERNAME Same as USER.
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
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"
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | security/sudo |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
su(1), stat(2), passwd(4), sudo.conf(4), sudoers(4), sudo_plugin(1m),
sudoreplay(1m), visudo(1m)
HISTORY
See the HISTORY file in the sudo distribution
(https://www.sudo.ws/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
(https://www.sudo.ws/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(4) 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
https://bugzilla.sudo.ws/
SUPPORT
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.
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
https://www.sudo.ws/license.html for complete details.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original community
source was downloaded from
http://www.sudo.ws/sudo/dist/sudo-1.8.18p1.tar.gz
Further information about this software can be found on the open source
community website at http://www.sudo.ws/.
Sudo 1.8.18p1 January 19, 2016 SUDO(8)