1 Copyright (c) 1994-1996, 1998-2005, 2007
2 Todd C. Miller <Todd.Miller@courtesan.com>
4 Permission to use, copy, modify, and distribute this software for any
5 purpose with or without fee is hereby granted, provided that the above
6 copyright notice and this permission notice appear in all copies.
8 THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
17 Sponsored in part by the Defense Advanced Research Projects
18 Agency (DARPA) and Air Force Research Laboratory, Air Force
19 Materiel Command, USAF, under agreement number F39502-99-1-0512.
21 $Sudo: sudo.pod,v 1.70.2.24 2008/02/19 18:22:11 millert Exp $
26 sudo, sudoedit - execute a command as another user
30 B<sudo> B<-h> | B<-K> | B<-k> | B<-L> | B<-l> | B<-V> | B<-v>
33 S<[B<-a> I<auth_type>]>
34 S<[B<-c> I<class>|I<->]>
36 S<[B<-r> I<role>]> S<[B<-t> I<type>]>
37 S<[B<-u> I<username>|I<#uid>]>
38 S<[B<VAR>=I<value>]> S<{B<-i> | B<-s> | I<command>}>
41 S<[B<-a> I<auth_type>]>
42 S<[B<-c> I<class>|I<->]>
43 S<[B<-p> I<prompt>]> S<[B<-u> I<username>|I<#uid>]>
48 B<sudo> allows a permitted user to execute a I<command> as the
49 superuser or another user, as specified in the I<sudoers> file.
50 The real and effective uid and gid are set to match those of the
51 target user as specified in the passwd file and the group vector
52 is initialized based on the group file (unless the B<-P> option was
53 specified). If the invoking user is root or if the target user is
54 the same as the invoking user, no password is required. Otherwise,
55 B<sudo> requires that users authenticate themselves with a password
56 by default (NOTE: in the default configuration this is the user's
57 password, not the root password). Once a user has been authenticated,
58 a timestamp is updated and the user may then use sudo without a
59 password for a short period of time (C<@timeout@> minutes unless
60 overridden in I<sudoers>).
62 When invoked as B<sudoedit>, the B<-e> option (described below),
65 B<sudo> determines who is an authorized user by consulting the file
66 F<@sysconfdir@/sudoers>. By giving B<sudo> the B<-v> flag, a user
67 can update the time stamp without running a I<command>. The password
68 prompt itself will also time out if the user's password is not
69 entered within C<@password_timeout@> minutes (unless overridden via
72 If a user who is not listed in the I<sudoers> file tries to run a
73 command via B<sudo>, mail is sent to the proper authorities, as
74 defined at configure time or in the I<sudoers> file (defaults to
75 C<@mailto@>). Note that the mail will not be sent if an unauthorized
76 user tries to run sudo with the B<-l> or B<-v> flags. This allows
77 users to determine for themselves whether or not they are allowed
80 If B<sudo> is run by root and the C<SUDO_USER> environment variable
81 is set, B<sudo> will use this value to determine who the actual
82 user is. This can be used by a user to log commands through sudo
83 even when a root shell has been invoked. It also allows the B<-e>
84 flag to remain useful even when being run via a sudo-run script or
85 program. Note however, that the sudoers lookup is still done for
86 root, not the user specified by C<SUDO_USER>.
88 B<sudo> can log both successful and unsuccessful attempts (as well
89 as errors) to syslog(3), a log file, or both. By default B<sudo>
90 will log via syslog(3) but this is changeable at configure time
91 or via the I<sudoers> file.
95 B<sudo> accepts the following command line options:
101 The B<-a> (I<authentication type>) option causes B<sudo> to use the
102 specified authentication type when validating the user, as allowed
103 by F</etc/login.conf>. The system administrator may specify a list
104 of sudo-specific authentication methods by adding an "auth-sudo"
105 entry in F</etc/login.conf>. This option is only available on systems
106 that support BSD authentication.
110 The B<-b> (I<background>) option tells B<sudo> to run the given
111 command in the background. Note that if you use the B<-b>
112 option you cannot use shell job control to manipulate the process.
116 The B<-c> (I<class>) option causes B<sudo> to run the specified command
117 with resources limited by the specified login class. The I<class>
118 argument can be either a class name as defined in C</etc/login.conf>,
119 or a single '-' character. Specifying a I<class> of C<-> indicates
120 that the command should be run restricted by the default login
121 capabilities for the user the command is run as. If the I<class>
122 argument specifies an existing user class, the command must be run
123 as root, or the B<sudo> command must be run from a shell that is already
124 root. This option is only available on systems with BSD login classes.
128 The B<-E> (I<preserve> I<environment>) option will override the
129 I<env_reset> option in L<sudoers(5)>). It is only
130 available when either the matching command has the C<SETENV> tag
131 or the I<setenv> option is set in L<sudoers(5)>.
135 The B<-e> (I<edit>) option indicates that, instead of running
136 a command, the user wishes to edit one or more files. In lieu
137 of a command, the string "sudoedit" is used when consulting
138 the I<sudoers> file. If the user is authorized by I<sudoers>
139 the following steps are taken:
145 Temporary copies are made of the files to be edited with the owner
146 set to the invoking user.
150 The editor specified by the C<VISUAL> or C<EDITOR> environment
151 variables is run to edit the temporary files. If neither C<VISUAL>
152 nor C<EDITOR> are set, the program listed in the I<editor> I<sudoers>
157 If they have been modified, the temporary files are copied back to
158 their original location and the temporary versions are removed.
162 If the specified file does not exist, it will be created. Note
163 that unlike most commands run by B<sudo>, the editor is run with
164 the invoking user's environment unmodified. If, for some reason,
165 B<sudo> is unable to update a file with its edited version, the
166 user will receive a warning and the edited copy will remain in a
171 The B<-H> (I<HOME>) option sets the C<HOME> environment variable
172 to the homedir of the target user (root by default) as specified
173 in passwd(5). By default, B<sudo> does not modify C<HOME>
174 (see I<set_home> and I<always_set_home> in L<sudoers(5)>).
178 The B<-h> (I<help>) option causes B<sudo> to print a usage message and exit.
182 The B<-i> (I<simulate initial login>) option runs the shell specified
183 in the L<passwd(5)> entry of the user that the command is
184 being run as. The command name argument given to the shell begins
185 with a `C<->' to tell the shell to run as a login shell. B<sudo>
186 attempts to change to that user's home directory before running the
187 shell. It also initializes the environment, leaving I<TERM>
188 unchanged, setting I<HOME>, I<SHELL>, I<USER>, I<LOGNAME>, and
189 I<PATH>, and unsetting all other environment variables. Note that
190 because the shell to use is determined before the I<sudoers> file
191 is parsed, a I<runas_default> setting in I<sudoers> will specify
192 the user to run the shell as but will not affect which shell is
197 The B<-K> (sure I<kill>) option is like B<-k> except that it removes
198 the user's timestamp entirely. Like B<-k>, this option does not
203 The B<-k> (I<kill>) option to B<sudo> invalidates the user's timestamp
204 by setting the time on it to the Epoch. The next time B<sudo> is
205 run a password will be required. This option does not require a password
206 and was added to allow a user to revoke B<sudo> permissions from a .logout
211 The B<-L> (I<list> defaults) option will list out the parameters
212 that may be set in a I<Defaults> line along with a short description
213 for each. This option is useful in conjunction with L<grep(1)>.
217 The B<-l> (I<list>) option will list out the allowed (and
218 forbidden) commands for the invoking user on the current host.
222 The B<-P> (I<preserve> I<group vector>) option causes B<sudo> to
223 preserve the invoking user's group vector unaltered. By default,
224 B<sudo> will initialize the group vector to the list of groups the
225 target user is in. The real and effective group IDs, however, are
226 still set to match the target user.
230 The B<-p> (I<prompt>) option allows you to override the default
231 password prompt and use a custom one. The following percent (`C<%>')
232 escapes are supported:
238 expanded to the local hostname including the domain name
239 (on if the machine's hostname is fully qualified or the I<fqdn>
240 I<sudoers> option is set)
244 expanded to the local hostname without the domain name
248 expanded to the user whose password is being asked for (respects the
249 I<rootpw>, I<targetpw> and I<runaspw> flags in I<sudoers>)
253 expanded to the login name of the user the command will
254 be run as (defaults to root)
258 expanded to the invoking user's login name
262 two consecutive C<%> characters are collapsed into a single C<%> character
268 The B<-r> (I<role>) option causes the new (SELinux) security context to
269 have the role specified by I<role>.
273 The B<-S> (I<stdin>) option causes B<sudo> to read the password from
274 the standard input instead of the terminal device.
278 The B<-s> (I<shell>) option runs the shell specified by the I<SHELL>
279 environment variable if it is set or the shell as specified
284 The B<-t> (I<type>) option causes the new (SELinux) security context to
285 have the type specified by I<type>. If no type is specified, the default
286 type is derived from the specified role.
290 The B<-u> (I<user>) option causes B<sudo> to run the specified
291 command as a user other than I<root>. To specify a I<uid> instead
292 of a I<username>, use I<#uid>. When running commands as a I<uid>,
293 many shells require that the '#' be escaped with a backslash ('\').
294 Note that if the I<targetpw> Defaults option is set (see L<sudoers(5)>)
295 it is not possible to run commands with a uid not listed in the
300 The B<-V> (I<version>) option causes B<sudo> to print the version
301 number and exit. If the invoking user is already root the B<-V>
302 option will print out a list of the defaults B<sudo> was compiled
303 with as well as the machine's local network addresses.
307 If given the B<-v> (I<validate>) option, B<sudo> will update the
308 user's timestamp, prompting for the user's password if necessary.
309 This extends the B<sudo> timeout for another C<@timeout@> minutes
310 (or whatever the timeout is set to in I<sudoers>) but does not run
315 The B<--> flag indicates that B<sudo> should stop processing command
316 line arguments. It is most useful in conjunction with the B<-s> flag.
320 Environment variables to be set for the command may also be passed
321 on the command line in the form of B<VAR>=I<value>, e.g.
322 B<LD_LIBRARY_PATH>=I</usr/local/pkg/lib>. Variables passed on the
323 command line are subject to the same restrictions as normal environment
324 variables with one important exception. If the I<setenv> option
325 is set in I<sudoers>, the command to be run has the C<SETENV> tag
326 set or the command matched is C<ALL>, the user may set variables
327 that would overwise be forbidden. See L<sudoers(5)> for more information.
331 Upon successful execution of a program, the return value from B<sudo>
332 will simply be the return value of the program that was executed.
334 Otherwise, B<sudo> quits with an exit value of 1 if there is a
335 configuration/permission problem or if B<sudo> cannot execute the
336 given command. In the latter case the error string is printed to
337 stderr. If B<sudo> cannot L<stat(2)> one or more entries in the user's
338 C<PATH> an error is printed on stderr. (If the directory does not
339 exist or if it is not really a directory, the entry is ignored and
340 no error is printed.) This should not happen under normal
341 circumstances. The most common reason for L<stat(2)> to return
342 "permission denied" is if you are running an automounter and one
343 of the directories in your C<PATH> is on a machine that is currently
346 =head1 SECURITY NOTES
348 B<sudo> tries to be safe when executing external commands.
350 There are two distinct ways to deal with environment variables.
351 By default, the I<env_reset> I<sudoers> option is enabled.
352 This causes commands to be executed with a minimal environment
353 containing C<TERM>, C<PATH>, C<HOME>, C<SHELL>, C<LOGNAME>, C<USER>
354 and C<USERNAME> in addition to variables from the invoking process
355 permitted by the I<env_check> and I<env_keep> I<sudoers> options.
356 There is effectively a whitelist for environment variables.
358 If, however, the I<env_reset> option is disabled in I<sudoers>, any
359 variables not explicitly denied by the I<env_check> and I<env_delete>
360 options are inherited from the invoking process. In this case,
361 I<env_check> and I<env_delete> behave like a blacklist. Since it
362 is not possible to blacklist all potentially dangerous environment
363 variables, use of the default I<env_reset> behavior is encouraged.
365 In all cases, environment variables with a value beginning with
366 C<()> are removed as they could be interpreted as B<bash> functions.
367 The list of environment variables that B<sudo> allows or denies is
368 contained in the output of C<sudo -V> when run as root.
370 Note that the dynamic linker on most operating systems will remove
371 variables that can control dynamic linking from the environment of
372 setuid executables, including B<sudo>. Depending on the operating
373 system this may include C<_RLD*>, C<DYLD_*>, C<LD_*>, C<LDR_*>,
374 C<LIBPATH>, C<SHLIB_PATH>, and others. These type of variables are
375 removed from the environment before B<sudo> even begins execution
376 and, as such, it is not possible for B<sudo> to preserve them.
378 To prevent command spoofing, B<sudo> checks "." and "" (both denoting
379 current directory) last when searching for a command in the user's
380 PATH (if one or both are in the PATH). Note, however, that the
381 C<PATH> environment variable is further modified in Debian because of
382 the use of the I<SECURE_PATH> build option.
384 B<sudo> will check the ownership of its timestamp directory
385 (F<@timedir@> by default) and ignore the directory's contents if
386 it is not owned by root or if it is writable by a user other than
387 root. On systems that allow non-root users to give away files via
388 L<chown(2)>, if the timestamp directory is located in a directory
389 writable by anyone (e.g., F</tmp>), it is possible for a user to
390 create the timestamp directory before B<sudo> is run. However,
391 because B<sudo> checks the ownership and mode of the directory and
392 its contents, the only damage that can be done is to "hide" files
393 by putting them in the timestamp dir. This is unlikely to happen
394 since once the timestamp dir is owned by root and inaccessible by
395 any other user, the user placing files there would be unable to get
396 them back out. To get around this issue you can use a directory
397 that is not world-writable for the timestamps (F</var/adm/sudo> for
398 instance) or create F<@timedir@> with the appropriate owner (root)
399 and permissions (0700) in the system startup files.
401 B<sudo> will not honor timestamps set far in the future.
402 Timestamps with a date greater than current_time + 2 * C<TIMEOUT>
403 will be ignored and sudo will log and complain. This is done to
404 keep a user from creating his/her own timestamp with a bogus
405 date on systems that allow users to give away files.
407 Please note that B<sudo> will normally only log the command it
408 explicitly runs. If a user runs a command such as C<sudo su> or
409 C<sudo sh>, subsequent commands run from that shell will I<not> be
410 logged, nor will B<sudo>'s access control affect them. The same
411 is true for commands that offer shell escapes (including most
412 editors). Because of this, care must be taken when giving users
413 access to commands via B<sudo> to verify that the command does not
414 inadvertently give the user an effective root shell. For more
415 information, please see the C<PREVENTING SHELL ESCAPES> section in
420 B<sudo> utilizes the following environment variables:
426 Default editor to use in B<-e> (sudoedit) mode if C<VISUAL> is not set
430 In B<-s> or B<-H> mode (or if sudo was configured with the
431 --enable-shell-sets-home option), set to homedir of the target user
435 Set to a sane value if the I<secure_path> sudoers option is set.
439 Used to determine shell to run with C<-s> option
443 Used as the default password prompt
445 =item C<SUDO_COMMAND>
447 Set to the command run by sudo
451 Set to the login of the user who invoked sudo
455 Set to the uid of the user who invoked sudo
459 Set to the gid of the user who invoked sudo
463 If set, C<PS1> will be set to its value
467 Set to the target user (root unless the B<-u> option is specified)
471 Default editor to use in B<-e> (sudoedit) mode
479 =item F<@sysconfdir@/sudoers>
481 List of who can run what
485 Directory containing timestamps
491 Note: the following examples assume suitable L<sudoers(5)> entries.
493 To get a file listing of an unreadable directory:
495 $ sudo ls /usr/local/protected
497 To list the home directory of user yazza on a machine where the
498 file system holding ~yazza is not exported as root:
500 $ sudo -u yazza ls ~yazza
502 To edit the F<index.html> file as user www:
504 $ sudo -u www vi ~www/htdocs/index.html
506 To shutdown a machine:
508 $ sudo shutdown -r +15 "quick reboot"
510 To make a usage listing of the directories in the /home
511 partition. Note that this runs the commands in a sub-shell
512 to make the C<cd> and file redirection work.
514 $ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
518 L<grep(1)>, L<su(1)>, L<stat(2)>,
520 L<passwd(5)>, L<sudoers(5)>, L<visudo(8)>
522 The file /usr/share/doc/sudo/OPTIONS describes the options used for building
523 the Debian version of sudo, some of which change default behaviors documented
524 elsewhere in this document.
528 Many people have worked on B<sudo> over the years; this
529 version consists of code written primarily by:
534 See the HISTORY file in the B<sudo> distribution or visit
535 http://www.sudo.ws/sudo/history.html for a short history
540 There is no easy way to prevent a user from gaining a root shell
541 if that user is allowed to run arbitrary commands via B<sudo>.
542 Also, many programs (such as editors) allow the user to run commands
543 via shell escapes, thus avoiding B<sudo>'s checks. However, on
544 most systems it is possible to prevent shell escapes with B<sudo>'s
545 I<noexec> functionality. See the L<sudoers(5)> manual
548 It is not meaningful to run the C<cd> command directly via sudo, e.g.,
550 $ sudo cd /usr/local/protected
552 since when the command exits the parent process (your shell) will
553 still be the same. Please see the EXAMPLES section for more information.
555 If users have sudo C<ALL> there is nothing to prevent them from
556 creating their own program that gives them a root shell regardless
557 of any '!' elements in the user specification.
559 Running shell scripts via B<sudo> can expose the same kernel bugs that
560 make setuid shell scripts unsafe on some operating systems (if your OS
561 has a /dev/fd/ directory, setuid shell scripts are generally safe).
565 If you feel you have found a bug in B<sudo>, please submit a bug report
566 at http://www.sudo.ws/sudo/bugs/
570 Limited free support is available via the sudo-users mailing list,
571 see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
576 B<sudo> is provided ``AS IS'' and any express or implied warranties,
577 including, but not limited to, the implied warranties of merchantability
578 and fitness for a particular purpose are disclaimed. See the LICENSE
579 file distributed with B<sudo> or http://www.sudo.ws/sudo/license.html
580 for complete details.