sudo

Execute a command as another user.
Allows a permitted user to execute a command as the superuser or another user, as specified in the sudoers file.

Syntax
       sudo [ -H ] [-P ] [-S ] [ -b ] command

       sudo [ -p prompt ] [ -c class|- ]
               [ -a auth_type ] [ -u username|#uid ] command

       sudo -V | -h | -l | -L | -v | -k | -K | -s command

Options
   -a  The -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
	      where sudo has been configured with the --with-bsdauth option.

   -b  The -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.

   -c  The -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 where sudo has been configured with the --with-logincap option.

   -h  The -h (help) option causes sudo to print a usage message and exit.

   -H  The -H (HOME) option sets the HOME environment variable to the homedir
	      of the target user (root by default) as specified in
	      passwd(5).  By default, sudo does not modify HOME.

   -k  The -k (kill) option to sudo invalidates the user's timestamp by setting the
	      time on it to the epoch.	 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.

   -K  The -K (sure kill) option to sudo removes the user's timestamp
	      entirely.  Likewise, this option does not require a password.

   -l  The -l (list) option will list out the allowed (and forbidden) commands
	      for the user on the current host.

   -L  The -L (list defaults) option will list out the parameters that may
	      be set in a Defaults line along with a short description for each.
	      This option is useful in conjunction with grep(1).

   -p  The -p (prompt) option allows you to override the default password
	      prompt and use a custom one.	 If the password prompt contains the
	      %u escape, %u will be replaced with the user's login name.
	      Similarly, %h will be replaced with the local hostname.

   -P  The -P (preserve group vector) option causes sudo to preserve the
	      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.

   -s  The -s (shell) option runs the shell specified by the SHELL environment
	      variable if it is set or the shell as specified in passwd(5).

   -S  The -S (stdin) option causes sudo to read the password from standard
	     input instead of the terminal device.

   -u  The -u (user) option causes sudo to run the specified command as a
	      user other than root.  To specify a uid instead of a username, use #uid.

   -v  If given the -v (validate) option, sudo will update the user's
	      timestamp, prompting for 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.

   -V  The -V (version) option causes sudo to print the version number and exit.
	      If the invoking user is already root the -V option will print out a list of the 
	      defaults sudo was compiled with as well as the machine's local network addresses.

   --  The -- flag indicates that sudo should stop processing command line
	      arguments.  It is most useful in conjunction with the -s flag.

By default, sudo requires that users authenticate themselves with a password (by default this is the user's password, not the root password). Once a user has been authenticated, a timestamp is updated and the user may then use sudo without a password for a short period of time (5 minutes unless overridden in sudoers).

sudo determines who is an authorized user by consulting the file /etc/sudoers. By giving sudo the -v flag a user can update the time stamp without running a command. The password prompt itself will also time out if the user's password is not entered within 0 minutes (unless overridden via sudoers).
If a user who is not listed in the sudoers file tries to run a command via sudo, mail is sent to the proper authorities, as defined at configure time or the sudoers file (defaults to root). Note that the mail will not be sent if an unauthorized user tries to run sudo with the -l or -v flags. This allows users to determine for themselves whether or not they are allowed to use sudo.
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 at configure time or via the sudoers file.

sudo will 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 will not be logged, nor will sudo's access control affect them. The same is true for commands that offer shell escapes (including most editors). Because of this, care must be taken when giving users access to commands via sudo to verify that the command does not inadvertantly give the user an effective root shell.

Return Values

Upon successful execution of a program, the return value from sudo will simply be the return value of the program that was executed. Otherwise, sudo quits with an exit value of 1 if there is a configuration/permission problem or if sudo cannot execute the given command.

Environment

sudo uses the environment variables: HOME, PATH, SHELL, USER, SUDO_PROMPT, SUDO_COMMAND, SUDO_USER, SUDO_UID, SUDO_GID and SUDO_PS1.

Files

/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps

Examples

The following examples assume suitable sudoers(5) entries.

Get a file listing of an unreadable directory:

$ sudo ls /usr/local/protected

Run the last command as root, useful when you forget to use sudo for a command. !! grabs the last run command.

sudo !!

List the home directory of user yazza on a machine where the file system holding ~yazza is not exported as root:

$ sudo -u yazza ls ~yazza

Edit the index.html file as user JDoe:

$ sudo -u JDoe vi ~www/htdocs/index.html

Shutdown a machine:

$ sudo shutdown -r +15 "quick reboot"

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"

"If you don't like your reality change it" ~ Richard Bandler

Related:

sudo man page - Apple.com
login - log into the computer
su - Substitute user identity
stat(2)
sudoers(5)
passwd - Modify a user password
visudo(8)
grep - Search file(s) for lines that match a given pattern
www.sudo.ws - Todd Miller, sudo maintainer
Password generator


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