Annotation of src/usr.bin/sudo/sudo.pod, Revision 1.8
1.1 millert 1: =cut
1.6 millert 2: Copyright (c) 1994-1996, 1998-2005, 2007
3: Todd C. Miller <Todd.Miller@courtesan.com>
1.1 millert 4:
5: Permission to use, copy, modify, and distribute this software for any
6: purpose with or without fee is hereby granted, provided that the above
7: copyright notice and this permission notice appear in all copies.
8:
9: THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10: WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11: MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12: ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13: WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14: ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15: OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16: ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
17:
18: Sponsored in part by the Defense Advanced Research Projects
19: Agency (DARPA) and Air Force Research Laboratory, Air Force
20: Materiel Command, USAF, under agreement number F39502-99-1-0512.
21:
1.8 ! millert 22: $Sudo: sudo.pod,v 1.70.2.20 2008/01/05 23:59:42 millert Exp $
1.1 millert 23: =pod
24:
25: =head1 NAME
26:
27: sudo, sudoedit - execute a command as another user
28:
29: =head1 SYNOPSIS
30:
31: B<sudo> B<-h> | B<-K> | B<-k> | B<-L> | B<-l> | B<-V> | B<-v>
32:
33: B<sudo> [B<-bEHPS>] S<[B<-a> I<auth_type>]>
34: S<[B<-c> I<class>|I<->]> S<[B<-p> I<prompt>]> S<[B<-u> I<username>|I<#uid>]>
35: S<[B<VAR>=I<value>]> S<{B<-i> | B<-s> | I<command>}>
36:
37: B<sudoedit> [B<-S>] S<[B<-a> I<auth_type>]> S<[B<-c> I<class>|I<->]>
38: S<[B<-p> I<prompt>]> S<[B<-u> I<username>|I<#uid>]>
39: file ...
40:
41: =head1 DESCRIPTION
42:
43: B<sudo> allows a permitted user to execute a I<command> as the
44: superuser or another user, as specified in the I<sudoers> file.
45: The real and effective uid and gid are set to match those of the
46: target user as specified in the passwd file and the group vector
47: is initialized based on the group file (unless the B<-P> option was
48: specified). If the invoking user is root or if the target user is
49: the same as the invoking user, no password is required. Otherwise,
50: B<sudo> requires that users authenticate themselves with a password
51: by default (NOTE: in the default configuration this is the user's
52: password, not the root password). Once a user has been authenticated,
53: a timestamp is updated and the user may then use sudo without a
54: password for a short period of time (C<@timeout@> minutes unless
55: overridden in I<sudoers>).
56:
57: When invoked as B<sudoedit>, the B<-e> option (described below),
58: is implied.
59:
60: B<sudo> determines who is an authorized user by consulting the file
61: F<@sysconfdir@/sudoers>. By giving B<sudo> the B<-v> flag, a user
1.6 millert 62: can update the time stamp without running a I<command>. The password
1.1 millert 63: prompt itself will also time out if the user's password is not
64: entered within C<@password_timeout@> minutes (unless overridden via
65: I<sudoers>).
66:
67: If a user who is not listed in the I<sudoers> file tries to run a
68: command via B<sudo>, mail is sent to the proper authorities, as
69: defined at configure time or in the I<sudoers> file (defaults to
70: C<@mailto@>). Note that the mail will not be sent if an unauthorized
71: user tries to run sudo with the B<-l> or B<-v> flags. This allows
72: users to determine for themselves whether or not they are allowed
73: to use B<sudo>.
74:
75: If B<sudo> is run by root and the C<SUDO_USER> environment variable
76: is set, B<sudo> will use this value to determine who the actual
77: user is. This can be used by a user to log commands through sudo
78: even when a root shell has been invoked. It also allows the B<-e>
79: flag to remain useful even when being run via a sudo-run script or
80: program. Note however, that the sudoers lookup is still done for
81: root, not the user specified by C<SUDO_USER>.
82:
83: B<sudo> can log both successful and unsuccessful attempts (as well
84: as errors) to syslog(3), a log file, or both. By default B<sudo>
85: will log via syslog(3) but this is changeable at configure time
86: or via the I<sudoers> file.
87:
88: =head1 OPTIONS
89:
90: B<sudo> accepts the following command line options:
91:
92: =over 4
93:
94: =item -a
95:
96: The B<-a> (I<authentication type>) option causes B<sudo> to use the
97: specified authentication type when validating the user, as allowed
1.6 millert 98: by F</etc/login.conf>. The system administrator may specify a list
1.1 millert 99: of sudo-specific authentication methods by adding an "auth-sudo"
1.6 millert 100: entry in F</etc/login.conf>. This option is only available on systems
1.1 millert 101: that support BSD authentication.
102:
103: =item -b
104:
105: The B<-b> (I<background>) option tells B<sudo> to run the given
106: command in the background. Note that if you use the B<-b>
107: option you cannot use shell job control to manipulate the process.
108:
109: =item -c
110:
111: The B<-c> (I<class>) option causes B<sudo> to run the specified command
112: with resources limited by the specified login class. The I<class>
113: argument can be either a class name as defined in C</etc/login.conf>,
114: or a single '-' character. Specifying a I<class> of C<-> indicates
115: that the command should be run restricted by the default login
116: capabilities for the user the command is run as. If the I<class>
117: argument specifies an existing user class, the command must be run
118: as root, or the B<sudo> command must be run from a shell that is already
119: root. This option is only available on systems with BSD login classes.
120:
121: =item -E
122:
1.6 millert 123: The B<-E> (I<preserve> I<environment>) option will override the
1.1 millert 124: I<env_reset> option in L<sudoers(5)>). It is only
125: available when either the matching command has the C<SETENV> tag
126: or the I<setenv> option is set in L<sudoers(5)>.
127:
128: =item -e
129:
130: The B<-e> (I<edit>) option indicates that, instead of running
131: a command, the user wishes to edit one or more files. In lieu
132: of a command, the string "sudoedit" is used when consulting
133: the I<sudoers> file. If the user is authorized by I<sudoers>
134: the following steps are taken:
135:
1.6 millert 136: =over 4
1.1 millert 137:
138: =item 1.
139:
140: Temporary copies are made of the files to be edited with the owner
141: set to the invoking user.
142:
143: =item 2.
144:
145: The editor specified by the C<VISUAL> or C<EDITOR> environment
146: variables is run to edit the temporary files. If neither C<VISUAL>
147: nor C<EDITOR> are set, the program listed in the I<editor> I<sudoers>
148: variable is used.
149:
150: =item 3.
151:
152: If they have been modified, the temporary files are copied back to
153: their original location and the temporary versions are removed.
154:
155: =back
156:
157: If the specified file does not exist, it will be created. Note
158: that unlike most commands run by B<sudo>, the editor is run with
159: the invoking user's environment unmodified. If, for some reason,
160: B<sudo> is unable to update a file with its edited version, the
161: user will receive a warning and the edited copy will remain in a
162: temporary file.
163:
164: =item -H
165:
166: The B<-H> (I<HOME>) option sets the C<HOME> environment variable
167: to the homedir of the target user (root by default) as specified
168: in passwd(5). By default, B<sudo> does not modify C<HOME>
169: (see I<set_home> and I<always_set_home> in L<sudoers(5)>).
170:
171: =item -h
172:
173: The B<-h> (I<help>) option causes B<sudo> to print a usage message and exit.
174:
175: =item -i
176:
177: The B<-i> (I<simulate initial login>) option runs the shell specified
178: in the L<passwd(5)> entry of the user that the command is
179: being run as. The command name argument given to the shell begins
180: with a `C<->' to tell the shell to run as a login shell. B<sudo>
181: attempts to change to that user's home directory before running the
182: shell. It also initializes the environment, leaving I<TERM>
183: unchanged, setting I<HOME>, I<SHELL>, I<USER>, I<LOGNAME>, and
184: I<PATH>, and unsetting all other environment variables. Note that
185: because the shell to use is determined before the I<sudoers> file
186: is parsed, a I<runas_default> setting in I<sudoers> will specify
187: the user to run the shell as but will not affect which shell is
188: actually run.
189:
190: =item -K
191:
192: The B<-K> (sure I<kill>) option is like B<-k> except that it removes
193: the user's timestamp entirely. Like B<-k>, this option does not
194: require a password.
195:
196: =item -k
197:
198: The B<-k> (I<kill>) option to B<sudo> invalidates the user's timestamp
199: by setting the time on it to the Epoch. The next time B<sudo> is
200: run a password will be required. This option does not require a password
201: and was added to allow a user to revoke B<sudo> permissions from a .logout
202: file.
203:
204: =item -L
205:
206: The B<-L> (I<list> defaults) option will list out the parameters
207: that may be set in a I<Defaults> line along with a short description
208: for each. This option is useful in conjunction with L<grep(1)>.
209:
210: =item -l
211:
212: The B<-l> (I<list>) option will list out the allowed (and
213: forbidden) commands for the invoking user on the current host.
214:
215: =item -P
216:
1.6 millert 217: The B<-P> (I<preserve> I<group vector>) option causes B<sudo> to
1.1 millert 218: preserve the invoking user's group vector unaltered. By default,
219: B<sudo> will initialize the group vector to the list of groups the
220: target user is in. The real and effective group IDs, however, are
221: still set to match the target user.
222:
223: =item -p
224:
225: The B<-p> (I<prompt>) option allows you to override the default
226: password prompt and use a custom one. The following percent (`C<%>')
227: escapes are supported:
228:
1.6 millert 229: =over 4
1.1 millert 230:
231: =item C<%H>
232:
233: expanded to the local hostname including the domain name
234: (on if the machine's hostname is fully qualified or the I<fqdn>
235: I<sudoers> option is set)
236:
237: =item C<%h>
238:
239: expanded to the local hostname without the domain name
1.8 ! millert 240:
! 241: =item C<%p>
! 242:
! 243: expanded to the user whose password is being asked for (respects the
! 244: I<rootpw>, I<targetpw> and I<runaspw> flags in I<sudoers>)
1.1 millert 245:
246: =item C<%U>
247:
248: expanded to the login name of the user the command will
249: be run as (defaults to root)
250:
251: =item C<%u>
252:
253: expanded to the invoking user's login name
254:
255: =item C<%%>
256:
257: two consecutive C<%> characters are collapsed into a single C<%> character
258:
259: =back
260:
261: =item -S
262:
263: The B<-S> (I<stdin>) option causes B<sudo> to read the password from
264: the standard input instead of the terminal device.
265:
266: =item -s
267:
268: The B<-s> (I<shell>) option runs the shell specified by the I<SHELL>
269: environment variable if it is set or the shell as specified
270: in L<passwd(5)>.
271:
272: =item -u
273:
1.6 millert 274: The B<-u> (I<user>) option causes B<sudo> to run the specified
275: command as a user other than I<root>. To specify a I<uid> instead
276: of a I<username>, use I<#uid>. When running commands as a I<uid>,
277: many shells require that the '#' be escaped with a backslash ('\').
278: Note that if the I<targetpw> Defaults option is set (see L<sudoers(5)>)
279: it is not possible to run commands with a uid not listed in the
280: password database.
1.1 millert 281:
282: =item -V
283:
284: The B<-V> (I<version>) option causes B<sudo> to print the version
285: number and exit. If the invoking user is already root the B<-V>
286: option will print out a list of the defaults B<sudo> was compiled
287: with as well as the machine's local network addresses.
288:
289: =item -v
290:
291: If given the B<-v> (I<validate>) option, B<sudo> will update the
292: user's timestamp, prompting for the user's password if necessary.
293: This extends the B<sudo> timeout for another C<@timeout@> minutes
294: (or whatever the timeout is set to in I<sudoers>) but does not run
295: a command.
296:
297: =item --
298:
299: The B<--> flag indicates that B<sudo> should stop processing command
300: line arguments. It is most useful in conjunction with the B<-s> flag.
301:
302: =back
303:
304: Environment variables to be set for the command may also be passed
305: on the command line in the form of B<VAR>=I<value>, e.g.
306: B<LD_LIBRARY_PATH>=I</usr/local/pkg/lib>. Variables passed on the
307: command line are subject to the same restrictions as normal environment
308: variables with one important exception. If the I<setenv> option
1.7 millert 309: is set in I<sudoers>, the command to be run has the C<SETENV> tag
310: set or the command matched is C<ALL>, the user may set variables
311: that would overwise be forbidden. See L<sudoers(5)> for more information.
1.1 millert 312:
313: =head1 RETURN VALUES
314:
315: Upon successful execution of a program, the return value from B<sudo>
316: will simply be the return value of the program that was executed.
317:
318: Otherwise, B<sudo> quits with an exit value of 1 if there is a
319: configuration/permission problem or if B<sudo> cannot execute the
320: given command. In the latter case the error string is printed to
321: stderr. If B<sudo> cannot L<stat(2)> one or more entries in the user's
322: C<PATH> an error is printed on stderr. (If the directory does not
323: exist or if it is not really a directory, the entry is ignored and
324: no error is printed.) This should not happen under normal
325: circumstances. The most common reason for L<stat(2)> to return
326: "permission denied" is if you are running an automounter and one
327: of the directories in your C<PATH> is on a machine that is currently
328: unreachable.
329:
330: =head1 SECURITY NOTES
331:
332: B<sudo> tries to be safe when executing external commands.
333:
334: There are two distinct ways to deal with environment variables.
335: By default, the I<env_reset> I<sudoers> option is enabled.
336: This causes commands to be executed with a minimal environment
337: containing C<TERM>, C<PATH>, C<HOME>, C<SHELL>, C<LOGNAME>, C<USER>
338: and C<USERNAME> in addition to variables from the invoking process
339: permitted by the I<env_check> and I<env_keep> I<sudoers> options.
340: There is effectively a whitelist for environment variables.
341:
342: If, however, the I<env_reset> option is disabled in I<sudoers>, any
343: variables not explicitly denied by the I<env_check> and I<env_delete>
344: options are inherited from the invoking process. In this case,
345: I<env_check> and I<env_delete> behave like a blacklist. Since it
346: is not possible to blacklist all potentially dangerous environment
347: variables, use of the default I<env_reset> behavior is encouraged.
348:
349: In all cases, environment variables with a value beginning with
350: C<()> are removed as they could be interpreted as B<bash> functions.
351: The list of environment variables that B<sudo> allows or denies is
352: contained in the output of C<sudo -V> when run as root.
353:
354: Note that the dynamic linker on most operating systems will remove
355: variables that can control dynamic linking from the environment of
356: setuid executables, including B<sudo>. Depending on the operating
357: system this may include C<_RLD*>, C<DYLD_*>, C<LD_*>, C<LDR_*>,
358: C<LIBPATH>, C<SHLIB_PATH>, and others. These type of variables are
359: removed from the environment before B<sudo> even begins execution
360: and, as such, it is not possible for B<sudo> to preserve them.
361:
362: To prevent command spoofing, B<sudo> checks "." and "" (both denoting
363: current directory) last when searching for a command in the user's
364: PATH (if one or both are in the PATH). Note, however, that the
365: actual C<PATH> environment variable is I<not> modified and is passed
366: unchanged to the program that B<sudo> executes.
367:
368: B<sudo> will check the ownership of its timestamp directory
369: (F<@timedir@> by default) and ignore the directory's contents if
370: it is not owned by root or if it is writable by a user other than
371: root. On systems that allow non-root users to give away files via
372: L<chown(2)>, if the timestamp directory is located in a directory
373: writable by anyone (e.g., F</tmp>), it is possible for a user to
374: create the timestamp directory before B<sudo> is run. However,
375: because B<sudo> checks the ownership and mode of the directory and
376: its contents, the only damage that can be done is to "hide" files
377: by putting them in the timestamp dir. This is unlikely to happen
378: since once the timestamp dir is owned by root and inaccessible by
379: any other user, the user placing files there would be unable to get
380: them back out. To get around this issue you can use a directory
381: that is not world-writable for the timestamps (F</var/adm/sudo> for
382: instance) or create F<@timedir@> with the appropriate owner (root)
383: and permissions (0700) in the system startup files.
384:
385: B<sudo> will not honor timestamps set far in the future.
386: Timestamps with a date greater than current_time + 2 * C<TIMEOUT>
387: will be ignored and sudo will log and complain. This is done to
388: keep a user from creating his/her own timestamp with a bogus
389: date on systems that allow users to give away files.
390:
391: Please note that B<sudo> will normally only log the command it
392: explicitly runs. If a user runs a command such as C<sudo su> or
393: C<sudo sh>, subsequent commands run from that shell will I<not> be
394: logged, nor will B<sudo>'s access control affect them. The same
395: is true for commands that offer shell escapes (including most
396: editors). Because of this, care must be taken when giving users
397: access to commands via B<sudo> to verify that the command does not
398: inadvertently give the user an effective root shell. For more
399: information, please see the C<PREVENTING SHELL ESCAPES> section in
400: L<sudoers(5)>.
401:
402: =head1 ENVIRONMENT
403:
404: B<sudo> utilizes the following environment variables:
405:
1.6 millert 406: =over 16
407:
408: =item C<EDITOR>
409:
410: Default editor to use in B<-e> (sudoedit) mode if C<VISUAL> is not set
411:
412: =item C<HOME>
413:
414: In B<-s> or B<-H> mode (or if sudo was configured with the
415: --enable-shell-sets-home option), set to homedir of the target user
416:
417: =item C<PATH>
418:
419: Set to a sane value if the I<secure_path> sudoers option is set.
420:
421: =item C<SHELL>
1.1 millert 422:
1.6 millert 423: Used to determine shell to run with C<-s> option
1.1 millert 424:
1.6 millert 425: =item C<SUDO_PROMPT>
1.1 millert 426:
1.6 millert 427: Used as the default password prompt
1.1 millert 428:
1.6 millert 429: =item C<SUDO_COMMAND>
1.1 millert 430:
1.6 millert 431: Set to the command run by sudo
1.1 millert 432:
1.6 millert 433: =item C<SUDO_USER>
1.1 millert 434:
1.6 millert 435: Set to the login of the user who invoked sudo
1.1 millert 436:
1.6 millert 437: =item C<SUDO_UID>
1.1 millert 438:
1.6 millert 439: Set to the uid of the user who invoked sudo
1.1 millert 440:
1.6 millert 441: =item C<SUDO_GID>
1.1 millert 442:
1.6 millert 443: Set to the gid of the user who invoked sudo
444:
445: =item C<SUDO_PS1>
446:
447: If set, C<PS1> will be set to its value
448:
449: =item C<USER>
450:
451: Set to the target user (root unless the B<-u> option is specified)
452:
453: =item C<VISUAL>
454:
455: Default editor to use in B<-e> (sudoedit) mode
456:
457: =back
1.1 millert 458:
459: =head1 FILES
460:
1.5 millert 461: =over 4
462:
1.6 millert 463: =item F<@sysconfdir@/sudoers>C< >List of who can run what
1.4 millert 464:
1.6 millert 465: =item F<@timedir@>C< >Directory containing timestamps
1.5 millert 466:
467: =back
1.1 millert 468:
469: =head1 EXAMPLES
470:
471: Note: the following examples assume suitable L<sudoers(5)> entries.
472:
473: To get a file listing of an unreadable directory:
474:
475: $ sudo ls /usr/local/protected
476:
477: To list the home directory of user yazza on a machine where the
478: file system holding ~yazza is not exported as root:
479:
480: $ sudo -u yazza ls ~yazza
481:
482: To edit the F<index.html> file as user www:
483:
484: $ sudo -u www vi ~www/htdocs/index.html
485:
486: To shutdown a machine:
487:
488: $ sudo shutdown -r +15 "quick reboot"
489:
490: To make a usage listing of the directories in the /home
491: partition. Note that this runs the commands in a sub-shell
492: to make the C<cd> and file redirection work.
493:
494: $ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
495:
496: =head1 SEE ALSO
497:
498: L<grep(1)>, L<su(1)>, L<stat(2)>, L<login_cap(3)>, L<passwd(5)>,
499: L<sudoers(5)>, L<visudo(8)>
500:
501: =head1 AUTHORS
502:
503: Many people have worked on B<sudo> over the years; this
504: version consists of code written primarily by:
505:
506: Todd C. Miller
507: Chris Jepeway
508:
509: See the HISTORY file in the B<sudo> distribution or visit
510: http://www.sudo.ws/sudo/history.html for a short history
511: of B<sudo>.
512:
513: =head1 CAVEATS
514:
515: There is no easy way to prevent a user from gaining a root shell
516: if that user is allowed to run arbitrary commands via B<sudo>.
517: Also, many programs (such as editors) allow the user to run commands
518: via shell escapes, thus avoiding B<sudo>'s checks. However, on
519: most systems it is possible to prevent shell escapes with B<sudo>'s
520: I<noexec> functionality. See the L<sudoers(5)> manual
521: for details.
522:
523: It is not meaningful to run the C<cd> command directly via sudo, e.g.,
524:
525: $ sudo cd /usr/local/protected
526:
527: since when the command exits the parent process (your shell) will
528: still be the same. Please see the EXAMPLES section for more information.
529:
530: If users have sudo C<ALL> there is nothing to prevent them from
531: creating their own program that gives them a root shell regardless
532: of any '!' elements in the user specification.
533:
534: Running shell scripts via B<sudo> can expose the same kernel bugs that
535: make setuid shell scripts unsafe on some operating systems (if your OS
536: has a /dev/fd/ directory, setuid shell scripts are generally safe).
537:
538: =head1 BUGS
539:
540: If you feel you have found a bug in B<sudo>, please submit a bug report
541: at http://www.sudo.ws/sudo/bugs/
542:
543: =head1 SUPPORT
544:
545: Limited free support is available via the sudo-users mailing list,
546: see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
547: search the archives.
548:
549: =head1 DISCLAIMER
550:
551: B<sudo> is provided ``AS IS'' and any express or implied warranties,
552: including, but not limited to, the implied warranties of merchantability
553: and fitness for a particular purpose are disclaimed. See the LICENSE
554: file distributed with B<sudo> or http://www.sudo.ws/sudo/license.html
555: for complete details.
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