sudo, sudoedit

execute a command as another user

sudo -h | -K | -k | -V

sudo -v [-AknS] [-g group name|#gid] [-p prompt] [-u uname|#uid]

sudo -l[l] [-AknS] [-g groupname|#gid] [-p prompt] [-U uname] [-u uname|#uid] [command]
sudo [‑AbEHnPS] [‑C fd] [‑g groupname|#gid] [‑p prompt] [‑r role] [‑t type] [‑u uname|#uid] [VAR=value] [‑i | ‑s] [command]

sudoedit[-AnS] [-C fd] [-g groupname|#gid] [-p prompt] [-u uname|#uid] file

Execute a command as the superuser or another user,
The real and effective uid and gid are set to match those of the target user, the group vector may be initialized based on the group database

As usual, different systems may have different versions of this utility, check man sudo for available options and exact operations
As of 5/8/13 this is taken from man of March 15, 2012 on a system with Sudo version1.8.5p2

See Sudo.ws for 1.8.6p8, released on April 11, 2013.

Frequently used by admins to perform an administrative function.
This allows login/auditing commands as syslog is sent a notice similar to

sudo[9115]:  uunnamme : TTY=ttys000 ; PWD=/private/var/log ; USER=root ; COMMAND=/bin/kill -hup 51

Sometimes used by admins to run a command for a user.

Redirections are started before user ID is changed.

This means that:
/etc > sudo ls -l > listOfiles
will fail.

instead use:
/etc > sudo ls -l > ~/listOfiles

Supports a plugin architecture for security policies and input/output logging. Third parties can develop and distribute their own policy and I/O logging modules to work with the sudo front end. The default security policy is sudoers, which is configured in /etc/sudoers, or via LDAP. See PLUGINS

Security policy determines what privileges a user needs and may require that users authenticate within a time limit.
Credential caching may allow the user to run sudo again within a period of time without re-authentication.
-v updates cached credentials.
Security policies may log successful and failed attempts.
If an I/O plugin is configured, command's input and output may be logged.

As sudoedit the -e is implied.

-A askpass, a (possibly graphical) helper program might interagate the user and output the password to stdout.
$SUDO_ASKPASS is the path to the helper program.
/etc/sudo.conf may specify the askpass program, . 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.

Normally, if sudo requires a password, it will read it from the user's terminal.

-b background the given command. you cannot use shell job control to manipulate the process. Most interactive commands fail in background mode.
-C fd close file descriptors above fd which must be above the stder (3).
Normally, all open file descriptors above stderr are closed.
The security policy may only permit the user's ability to use -C when the administrator has enabled the closefrom_override .
-E environment preserve preserve existing environment variables.
-e (edit) edit one or more files. the string "sudoedit" is used when consulting the security policy.
  1. Temporary copies are made of the files to be edited with the owner set to the invoking user.
  2. The editor specified by the policy is run to edit the temporary files. The sudoers policy uses the SUDO_EDITOR, VISUAL and EDITOR environment variables (in that order). If none of SUDO_EDITOR, VISUAL or EDITOR are set, the first program listed in the editor sudoers(5) option is used.
  3. If 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 run the command with the primary group set to group . Normally, sudo runs a command with the primary group set to the one specified by the password database for the user the command is being run as (by default, root). 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 (HOME) 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 (help)
-i [command] (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 [command] (kill) cached credentials, will not update the user's cached credentials.
Does not require a password if used without command
Allows revoking sudo permissions from .logout .
-K ( Kill ) removes the user's cached credentials entirely and may not be used in conjunction with a command or other option. Does not require a password.
‑l[l] [command] lists the allowed (and forbidden) commands for the invoking user (or the user specified by -U ) on the current host.
If a command is specified and is permitted by the security policy, the fullyqualified path to the command is displayed along with any command line arguments.
If command is specified but not allowed, exit with a status 1.
-ll, or if -l is specified multiple times, a longer list format is used.
sudo -ll
Matching Defaults entries for dgerman on this host:
    env_reset,   reformatted. Notice strings with embedded spaces are in quotes
    env_keep+=BLOCKSIZE,        env_keep+="COLORFGBG COLORTERM",  env_keep+=__CF_USER_TEXT_ENCODING, 
    env_keep+="CHARSET LANG LANGUAGE LC_ALL LC_COLLATE LC_CTYPE", 
    env_keep+="LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME", 
    env_keep+="LINES COLUMNS",  env_keep+=LSCOLORS,
    env_keep+=SSH_AUTH_SOCK,    env_keep+=TZ,       env_keep+="DISPLAY XAUTHORIZATION XAUTHORITY", 
    env_keep+="EDITOR VISUAL", 
    env_keep+="HOME MAIL"

User dgerman may run the following commands on this host:

Sudoers entry:
    RunAsUsers: ALL
    Commands:
    ALL
-n (non-interactive) prevents prompting the user for a password. If a password is required for the command to run, sudo will display an error messages and exit.
-P (preserve group vector) 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 (prompt) default Password:
%h local host name without the domain name
%H host name including the domain name (on if the machine's host name is fully qualified or the fqdn option is set in sudoers
%p name of the user whose password is being requested (respects the rootpw, targetpw and runaspw flags in sudoers
%U login name of the user the command will be run as (defaults to root unless the -u is also specified)
%u invoking user's login name
%% a single % character
Override the system password prompt on systems that support PAM unless passprompt_override is disabled in sudoers.
-r role (role) causes the new (SELinux) security context to have the role specified by role.
-S (stdin) 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] (shell) 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 . If no command is specified, an interactive shell is executed.
-t type (type) 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 (other user) is used in conjunction with the -l 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 .
-u user (user) causes sudo to run the specified command as a user other than root. To specify a uid instead of a user name, use #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 is not set. Other security policies may not support this.
-V version output its version string and the version string of the security policy plugin and any I/O plugins. If the invoking user is root -V displays 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's password if necessary. For the sudoers plugin, this extends the sudo timeout for another 15 minutes (or whatever the timeout is set to in sudoers) but does not run a command. Not all security policies support cached credentials.
-- 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.

PLUGINS

Plugins are dynamically loaded based on the contents of the /etc/sudo.conf file. If no /etc/sudo.conf file is present, or it contains no Plugin lines, sudo will use the traditional sudoers security policy and I/O logging, which corresponds to the following /etc/sudo.conf file.
 
        # Default /etc/sudo.conf file
        #
        # Format:
        #   Plugin plugin_name plugin_path plugin_options ...
        #   Path askpass /path/to/askpass
        #   Path noexec /path/to/sudo_noexec.so
        #   Debug sudo /var/log/sudo_debug all@warn
        #   Set disable_coredump true
        #
        # The plugin_path is relative to /usr/libexec unless
        #   fully qualified.
        # The plugin_name corresponds to a global symbol in the plugin
        #   that contains the plugin interface structure.
        # The plugin_options are optional.
        #
        Plugin policy_plugin sudoers.so
        Plugin io_plugin sudoers.so
A Plugin line consists of the Plugin keyword, followed by the symbol_name and the path to the shared object containing the plugin. The symbol_name is the name of the struct policy_plugin or struct io_plugin in the plugin shared object. The path may be fully qualified or relative. If not fully qualified it is relative to the /usr/libexec directory. Any additional parameters after the path are passed as arguments to the plugin's open function. Lines that don't begin with Plugin, Path, Debug or Set are silently ignored. see sudo_plugin.

PATHS

A Path line consists of the Path keyword, followed by the name of the path to set and its value. E.g.
Path noexec /usr/lib/sudo/sudo_noexec.so Path askpass /usr/X11R6/bin/ssh-askpass
The following plugin-agnostic paths may be set in the /etc/sudo.conf file. askpass The fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when sudo is executed from a graphical (as opposed to text-based) application. The program specified by askpass should display the argument passed to it as the prompt and write the user's password to the standard output. The value of askpass may be overridden by the SUDO_ASKPASS environment variable. noexec The fully-qualified path to a shared library containing dummy versions of the execv(), execve() and fexecve() library functions that just return an error. This is used to implement the noexec functionality on systems that support LD_PRELOAD or its equivalent. Defaults to /usr/lib/sudo/sudo_noexec.so.

DEBUG FLAGS

Versions 1.8.4 and higher support a flexible debugging framework that can help track down what sudo is doing internally if there is a problem.

A Debug line consists of the Debug keyword, followed by the name of the program to debug (sudo, visudo, sudoreplay), the debug file name and a comma-separated list of debug flags. The debug flag syntax used by sudo and the sudoers plugin is subsystem@priority but the plugin is free to use a different format so long as it does not include a command ,. For instance:

Debug sudo /var/log/sudo_debug all@warn,plugin@info
would log all debugging statements at the warn level and higher in addition to those at the info level for the plugin subsystem.

Currently, only one Debug entry per program is supported. The sudo Debug entry is shared by the sudo front end, sudoedit and the plugins. A future release may add support for per-plugin Debug lines and/or support for multiple debugging files for a single program.

The priorities used by the sudo front end, in order of decreasing severity, are: crit, err, warn, notice, diag, info, trace and debug. Each priority, when specified, also includes all priorities higher than it. For example, a priority of notice would include debug messages logged at notice and higher. The following subsystems are used by sudo:
all matches every subsystem
args command line argument processing
conv user conversation
edit sudoedit
exec command execution
main sudo main function
netif network interface handling
pcomm communication with the plugin
plugin plugin configuration
pty pseudo-tty related code
selinux SELinux-specific handling
util utility functions
utmp utmp handling

RETURN VALUES

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 /etc/sudo.conf file.

Set disable_coredump false
By default, most operating systems disable core dumps from setuid programs, which includes sudo. To actually get a sudo core file you may need to enable core dumps for setuid processes. On BSD and Linux systems this is accomplished via the sysctl command, on Solaris the coreadm command can be used.

ENVIRONMENT

the following environment variables. The security policy has control over the content of the command's environment.
EDITOR Default editor to use in -e (sudoedit) mode if neither SUDO_EDITOR nor VISUAL is set
MAIL In -i mode or when env_reset is enabled in sudoers, set to the mail spool of the target user
HOME Set to the home directory of the target user if -i or -H are specified, env_reset or always_set_home are set in sudoers, or when the -s option is specified and set_home is set in sudoers
PATH May be overridden by the security policy.
SHELL Used to determine shell to run with -s option
SUDO_ASKPASS Specifies the path to a helper program used to read the password if no terminal is available or if the -A option is specified.
SUDO_COMMAND Set to the command run by sudo
SUDO_EDITOR Default editor to use in -e (sudoedit) mode
SUDO_GID Set to the group ID of the user who invoked sudo
SUDO_PROMPT Used as the default password prompt
SUDO_PS1 If set, PS1 will be set to its value for the program being run
SUDO_UID Set to the user ID of the user who invoked sudo
SUDO_USER Set to the login of the user who invoked sudo
USER Set to the target user (root unless the -u option is specified)
VISUAL Default editor to use in -e (sudoedit) mode if SUDO_EDITOR is not set

FILES

/etc/sudo.conf sudo front end configuration

EXAMPLES

Following examples assume a properly configured security policy. Get a file listing of an unreadable directory:
$ sudo ls /usr/local/protected
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
Edit index.html file as user www:
$ sudo -u www vi ~www/htdocs/index.html
View system logs only accessible to root and users in the adm group:
$ sudo -g adm view /var/log/syslog
Run an editor as jim with a different primary group:
$ sudo -u jim -g audio vi ~jim/sound.txt
Shutdown a machine:
$ sudo shutdown -r +15 "quick reboot"
Make a usage listing of the directories in the /home partition, 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

grep(1), su(1), stat(2), passwd(5), sudoers(5), sudo_plugin(8), sudoreplay(8), visudo(8) See the HISTORY file in the sudo distribution (sudo.ws for a brief history of 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.
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) module's noexec functionality.

It is not meaningful to run cd 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.

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

Submit a bug report at sudo.wd/sudo/bugs

SUPPORT

sudo-users mailing list, see sudo.ws/mailman/listinfo to subscribe or search the archives.

1.8.5 March 15, 2012

from smackerpro 5/8/13

# This file MUST be edited with the 'visudo' command as root.
# Otherwise syntax or file permission errors may prevent sudo from running.

# Host alias specification

# User alias specification

# Cmnd alias specification

# Defaults specification
Defaults    env_reset
Defaults    env_keep += "BLOCKSIZE"
Defaults    env_keep += "COLORFGBG COLORTERM"
Defaults    env_keep += "__CF_USER_TEXT_ENCODING"
Defaults    env_keep += "CHARSET LANG LANGUAGE LC_ALL LC_COLLATE LC_CTYPE"
Defaults    env_keep += "LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME"
Defaults    env_keep += "LINES COLUMNS"
Defaults    env_keep += "LSCOLORS"
Defaults    env_keep += "SSH_AUTH_SOCK"
Defaults    env_keep += "TZ"
Defaults    env_keep += "DISPLAY XAUTHORIZATION XAUTHORITY"
Defaults    env_keep += "EDITOR VISUAL"
Defaults    env_keep += "HOME MAIL"

# Runas alias specification

# User privilege specification
root    ALL=(ALL) ALL
%admin  ALL=(ALL) ALL

# Uncomment to allow people in group wheel to run all commands
# %wheel    ALL=(ALL) ALL

# Same thing without a password
# %wheel    ALL=(ALL) NOPASSWD: ALL

# Samples
# %users  ALL=/sbin/mount /cdrom,/sbin/umount /cdrom
# %users  localhost=/sbin/shutdown -h now