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       sudo - execute a	command	as another user

       sudo -V | -h | -l | -L |	-v | -k	| -K | -s | [ -H ] [-P ] [-S ] [ -b ]
       | [ -p prompt ] [ -c class|- ] [	-a auth_type ] [ -u username|#uid ]

       sudo allows a permitted user to execute a command as the	superuser or
       another user, as	specified in the sudoers file.	The real and effective
       uid and gid are set to match those of the target	user as	specified in
       the passwd file (the group vector is also initialized when the target
       user is not root).  By default, sudo requires that users	authenticate
       themselves with a password (NOTE: by default this is the	user's pass-
       word, 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
       /usr/local/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 5 min-
       utes (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 config-
       ure 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 sudo-
       ers file.

       sudo accepts the	following command line options:

       -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.

       -l  The -l (list) option	will list out the allowed (and forbidden) com-
	   mands 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).

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

       -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.

       -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.

       -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.

       -p  The -p (prompt) option allows you to	override the default password
	   prompt and use a custom one.	 The following percent (`%') escapes
	   are supported:

	   %u	   expanded to the invoking user's login name

	   %U	   expanded to the login name of the user the command will be
		   run as (defaults to root)

	   %h	   expanded to the local hostname without the domain name

	   %H	   expanded to the local hostname including the	domain name
		   (on if the machine's	hostname is fully qualified or the
		   fqdn	sudoers	option is set)

	   %%	   two consecutive % characters	are collaped into a single %

       -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 sin-
	   gle '-' character.  Specifying a class of - indicates that the com-
	   mand	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.

       -a  The -a (authentication type)	option causes sudo to use the speci-
	   fied	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.

       -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

       -s  The -s (shell) option runs the shell	specified by the SHELL envi-
	   ronment variable if it is set or the	shell as specified in

       -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.

       -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 (stdin) option causes	sudo to	read the password from stan-
	   dard	input instead of the terminal device.

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

       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 configura-
       tion/permission problem or if sudo cannot execute the given command.
       In the latter case the error string is printed to stderr.  If sudo can-
       not 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 auto-
       mounter and one of the directories in your PATH is on a machine that is
       currently unreachable.

       sudo tries to be	safe when executing external commands.	Variables that
       control how dynamic loading and binding is done can be used to subvert
       the program that	sudo runs.  To combat this the LD_*, _RLD_*,
       SHLIB_PATH (HP-UX only),	and LIBPATH (AIX only) environment variables
       are removed from	the environment	passed on to all commands executed.
       sudo will also remove the IFS, ENV, BASH_ENV, KRB_CONF, KRBCONFDIR,
       PATH_LOCALE, TERMINFO, TERMINFO_DIRS and	TERMPATH variables as they too
       can pose	a threat.  If the TERMCAP variable is set and is a pathname,
       it too is ignored.  Additionally, if the	LC_* or	LANGUAGE variables
       contain the / or	% characters, they are ignored.	 If sudo has been com-
       piled with SecurID support, the VAR_ACE,	USR_ACE	and DLC_ACE variables
       are cleared as well.  The list of environment variables that sudo
       clears is contained in the output of sudo -V when run as	root.

       To prevent command spoofing, sudo checks	"." and	"" (both denoting cur-
       rent 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.

       For security reasons, if	your OS	supports shared	libraries and does not
       disable user-defined library search paths for setuid programs (most
       do), you	should either use a linker option that disables	this behavior
       or link sudo statically.

       sudo will check the ownership of	its timestamp directory	(/var/run/sudo
       by default) and ignore the directory's contents if it is	not owned by
       root and	only writable by root.	On systems that	allow non-root users
       to give away files via chown(2),	if the timestamp directory is located
       in a directory writable by anyone (e.g.:	/tmp), it is possible for a
       user to create the timestamp 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 timestamp dir.  This	is unlikely to happen since
       once the	timestamp dir is owned by root and inaccessible	by any other
       user the	user placing files there would be unable to get	them back out.
       To get around this issue	you can	use a directory	that is	not world-
       writable	for the	timestamps (/var/adm/sudo for instance)	or create
       /var/run/sudo with the appropriate owner	(root) and permissions (0700)
       in the system startup files.

       sudo will not honor timestamps set far in the future.  Timestamps 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 timestamp with a bogus date on systems that allow users to
       give away files.

       Please note that	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	inadvertently give the user an effective root shell.

       Note: 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 yazza	on a machine where the
       filesystem holding ~yazza is not	exported as root:

	% sudo -u yazza	ls ~yazza

       To edit the index.html file as user www:

	% sudo -u www vi ~www/htdocs/index.html

       To shutdown 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"

       sudo utilizes the following environment variables:

	PATH		       Set to a	sane value if SECURE_PATH is set
	SHELL		       Used to determine shell to run with -s option
	USER		       Set to the target user (root unless the -u option
			       is specified)
	HOME		       In -s or	-H mode	(or if sudo was	configured with
			       the --enable-shell-sets-home option), set to
			       homedir of the target user.
	SUDO_PROMPT	       Used as the default password prompt
	SUDO_COMMAND	       Set to the command run by sudo
	SUDO_USER	       Set to the login	of the user who	invoked	sudo
	SUDO_UID	       Set to the uid of the user who invoked sudo
	SUDO_GID	       Set to the gid of the user who invoked sudo
	SUDO_PS1	       If set, PS1 will	be set to its value

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

       Many people have	worked on sudo over the	years; this version consists
       of code written primarily by:

	       Todd Miller
	       Chris Jepeway

       See the HISTORY file in the sudo	distribution or	visit for	a short	history	of sudo.

       If you feel you have found a bug	in sudo, please	submit a bug report at

       Sudo is provided	``AS IS'' and any express or implied warranties,
       including, but not limited to, the implied warranties of	merchantabil-
       ity and fitness for a particular	purpose	are disclaimed.	 See the
       LICENSE file distributed	with sudo for complete details.

       There is	no easy	way to prevent a user from gaining a root shell	if
       that user has access to commands	allowing shell escapes.

       If users	have sudo ALL there is nothing to prevent them from creating
       their own program that gives them a root	shell regardless of any	'!'
       elements	in the user specification.

       Running shell scripts via sudo can expose the same kernel bugs that
       make setuid shell scripts unsafe	on some	operating systems (if your OS
       supports	the /dev/fd/ directory,	setuid shell scripts are generally

       grep(1),	su(1), stat(2),	login_cap(3), sudoers(5), passwd(5), visudo(8)

1.6.7				March 13, 2003			       SUDO(8)


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