Annotation of src/usr.bin/sudo/sudo.pod, Revision 1.2
1.1 millert 1: =cut
2: Copyright (c) 1994-1996,1998-2007 Todd C. Miller <Todd.Miller@courtesan.com>
3:
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.
7:
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.
16:
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.
20:
21: $Sudo: sudo.pod,v 1.70.2.12 2007/07/26 14:04:54 millert Exp $
22: =pod
23:
24: =head1 NAME
25:
26: sudo, sudoedit - execute a command as another user
27:
28: =head1 SYNOPSIS
29:
30: B<sudo> B<-h> | B<-K> | B<-k> | B<-L> | B<-l> | B<-V> | B<-v>
31:
32: B<sudo> [B<-bEHPS>] S<[B<-a> I<auth_type>]>
33: S<[B<-c> I<class>|I<->]> S<[B<-p> I<prompt>]> S<[B<-u> I<username>|I<#uid>]>
34: S<[B<VAR>=I<value>]> S<{B<-i> | B<-s> | I<command>}>
35:
36: B<sudoedit> [B<-S>] S<[B<-a> I<auth_type>]> S<[B<-c> I<class>|I<->]>
37: S<[B<-p> I<prompt>]> S<[B<-u> I<username>|I<#uid>]>
38: file ...
39:
40: =head1 DESCRIPTION
41:
42: B<sudo> allows a permitted user to execute a I<command> as the
43: superuser or another user, as specified in the I<sudoers> file.
44: The real and effective uid and gid are set to match those of the
45: target user as specified in the passwd file and the group vector
46: is initialized based on the group file (unless the B<-P> option was
47: specified). If the invoking user is root or if the target user is
48: the same as the invoking user, no password is required. Otherwise,
49: B<sudo> requires that users authenticate themselves with a password
50: by default (NOTE: in the default configuration this is the user's
51: password, not the root password). Once a user has been authenticated,
52: a timestamp is updated and the user may then use sudo without a
53: password for a short period of time (C<@timeout@> minutes unless
54: overridden in I<sudoers>).
55:
56: When invoked as B<sudoedit>, the B<-e> option (described below),
57: is implied.
58:
59: B<sudo> determines who is an authorized user by consulting the file
60: F<@sysconfdir@/sudoers>. By giving B<sudo> the B<-v> flag, a user
61: can update the time stamp without running a I<command.> The password
62: prompt itself will also time out if the user's password is not
63: entered within C<@password_timeout@> minutes (unless overridden via
64: I<sudoers>).
65:
66: If a user who is not listed in the I<sudoers> file tries to run a
67: command via B<sudo>, mail is sent to the proper authorities, as
68: defined at configure time or in the I<sudoers> file (defaults to
69: C<@mailto@>). Note that the mail will not be sent if an unauthorized
70: user tries to run sudo with the B<-l> or B<-v> flags. This allows
71: users to determine for themselves whether or not they are allowed
72: to use B<sudo>.
73:
74: If B<sudo> is run by root and the C<SUDO_USER> environment variable
75: is set, B<sudo> will use this value to determine who the actual
76: user is. This can be used by a user to log commands through sudo
77: even when a root shell has been invoked. It also allows the B<-e>
78: flag to remain useful even when being run via a sudo-run script or
79: program. Note however, that the sudoers lookup is still done for
80: root, not the user specified by C<SUDO_USER>.
81:
82: B<sudo> can log both successful and unsuccessful attempts (as well
83: as errors) to syslog(3), a log file, or both. By default B<sudo>
84: will log via syslog(3) but this is changeable at configure time
85: or via the I<sudoers> file.
86:
87: =head1 OPTIONS
88:
89: B<sudo> accepts the following command line options:
90:
91: =over 4
92:
93: =item -a
94:
95: The B<-a> (I<authentication type>) option causes B<sudo> to use the
96: specified authentication type when validating the user, as allowed
97: by C</etc/login.conf>. The system administrator may specify a list
98: of sudo-specific authentication methods by adding an "auth-sudo"
99: entry in C</etc/login.conf>. This option is only available on systems
100: that support BSD authentication.
101:
102: =item -b
103:
104: The B<-b> (I<background>) option tells B<sudo> to run the given
105: command in the background. Note that if you use the B<-b>
106: option you cannot use shell job control to manipulate the process.
107:
108: =item -c
109:
110: The B<-c> (I<class>) option causes B<sudo> to run the specified command
111: with resources limited by the specified login class. The I<class>
112: argument can be either a class name as defined in C</etc/login.conf>,
113: or a single '-' character. Specifying a I<class> of C<-> indicates
114: that the command should be run restricted by the default login
115: capabilities for the user the command is run as. If the I<class>
116: argument specifies an existing user class, the command must be run
117: as root, or the B<sudo> command must be run from a shell that is already
118: root. This option is only available on systems with BSD login classes.
119:
120: =item -E
121:
122: The B<-E> (I<preserve> environment) option will override the
123: I<env_reset> option in L<sudoers(5)>). It is only
124: available when either the matching command has the C<SETENV> tag
125: or the I<setenv> option is set in L<sudoers(5)>.
126:
127: =item -e
128:
129: The B<-e> (I<edit>) option indicates that, instead of running
130: a command, the user wishes to edit one or more files. In lieu
131: of a command, the string "sudoedit" is used when consulting
132: the I<sudoers> file. If the user is authorized by I<sudoers>
133: the following steps are taken:
134:
135: =over 8
136:
137: =item 1.
138:
139: Temporary copies are made of the files to be edited with the owner
140: set to the invoking user.
141:
142: =item 2.
143:
144: The editor specified by the C<VISUAL> or C<EDITOR> environment
145: variables is run to edit the temporary files. If neither C<VISUAL>
146: nor C<EDITOR> are set, the program listed in the I<editor> I<sudoers>
147: variable is used.
148:
149: =item 3.
150:
151: If they have been modified, the temporary files are copied back to
152: their original location and the temporary versions are removed.
153:
154: =back
155:
156: If the specified file does not exist, it will be created. Note
157: that unlike most commands run by B<sudo>, the editor is run with
158: the invoking user's environment unmodified. If, for some reason,
159: B<sudo> is unable to update a file with its edited version, the
160: user will receive a warning and the edited copy will remain in a
161: temporary file.
162:
163: =item -H
164:
165: The B<-H> (I<HOME>) option sets the C<HOME> environment variable
166: to the homedir of the target user (root by default) as specified
167: in passwd(5). By default, B<sudo> does not modify C<HOME>
168: (see I<set_home> and I<always_set_home> in L<sudoers(5)>).
169:
170: =item -h
171:
172: The B<-h> (I<help>) option causes B<sudo> to print a usage message and exit.
173:
174: =item -i
175:
176: The B<-i> (I<simulate initial login>) option runs the shell specified
177: in the L<passwd(5)> entry of the user that the command is
178: being run as. The command name argument given to the shell begins
179: with a `C<->' to tell the shell to run as a login shell. B<sudo>
180: attempts to change to that user's home directory before running the
181: shell. It also initializes the environment, leaving I<TERM>
182: unchanged, setting I<HOME>, I<SHELL>, I<USER>, I<LOGNAME>, and
183: I<PATH>, and unsetting all other environment variables. Note that
184: because the shell to use is determined before the I<sudoers> file
185: is parsed, a I<runas_default> setting in I<sudoers> will specify
186: the user to run the shell as but will not affect which shell is
187: actually run.
188:
189: =item -K
190:
191: The B<-K> (sure I<kill>) option is like B<-k> except that it removes
192: the user's timestamp entirely. Like B<-k>, this option does not
193: require a password.
194:
195: =item -k
196:
197: The B<-k> (I<kill>) option to B<sudo> invalidates the user's timestamp
198: by setting the time on it to the Epoch. The next time B<sudo> is
199: run a password will be required. This option does not require a password
200: and was added to allow a user to revoke B<sudo> permissions from a .logout
201: file.
202:
203: =item -L
204:
205: The B<-L> (I<list> defaults) option will list out the parameters
206: that may be set in a I<Defaults> line along with a short description
207: for each. This option is useful in conjunction with L<grep(1)>.
208:
209: =item -l
210:
211: The B<-l> (I<list>) option will list out the allowed (and
212: forbidden) commands for the invoking user on the current host.
213:
214: =item -P
215:
216: The B<-P> (I<preserve> group vector) option causes B<sudo> to
217: preserve the invoking user's group vector unaltered. By default,
218: B<sudo> will initialize the group vector to the list of groups the
219: target user is in. The real and effective group IDs, however, are
220: still set to match the target user.
221:
222: =item -p
223:
224: The B<-p> (I<prompt>) option allows you to override the default
225: password prompt and use a custom one. The following percent (`C<%>')
226: escapes are supported:
227:
228: =over 8
229:
230: =item C<%H>
231:
232: expanded to the local hostname including the domain name
233: (on if the machine's hostname is fully qualified or the I<fqdn>
234: I<sudoers> option is set)
235:
236: =item C<%h>
237:
238: expanded to the local hostname without the domain name
239:
240: =item C<%U>
241:
242: expanded to the login name of the user the command will
243: be run as (defaults to root)
244:
245: =item C<%u>
246:
247: expanded to the invoking user's login name
248:
249: =item C<%%>
250:
251: two consecutive C<%> characters are collapsed into a single C<%> character
252:
253: =back
254:
255: =item -S
256:
257: The B<-S> (I<stdin>) option causes B<sudo> to read the password from
258: the standard input instead of the terminal device.
259:
260: =item -s
261:
262: The B<-s> (I<shell>) option runs the shell specified by the I<SHELL>
263: environment variable if it is set or the shell as specified
264: in L<passwd(5)>.
265:
266: =item -u
267:
268: The B<-u> (I<user>) option causes B<sudo> to run the specified command
269: as a user other than I<root>. To specify a I<uid> instead of a
270: I<username>, use I<#uid>. Note that if the I<targetpw> Defaults
271: option is set (see L<sudoers(5)>) it is not possible
272: to run commands with a uid not listed in the password database.
273:
274: =item -V
275:
276: The B<-V> (I<version>) option causes B<sudo> to print the version
277: number and exit. If the invoking user is already root the B<-V>
278: option will print out a list of the defaults B<sudo> was compiled
279: with as well as the machine's local network addresses.
280:
281: =item -v
282:
283: If given the B<-v> (I<validate>) option, B<sudo> will update the
284: user's timestamp, prompting for the user's password if necessary.
285: This extends the B<sudo> timeout for another C<@timeout@> minutes
286: (or whatever the timeout is set to in I<sudoers>) but does not run
287: a command.
288:
289: =item --
290:
291: The B<--> flag indicates that B<sudo> should stop processing command
292: line arguments. It is most useful in conjunction with the B<-s> flag.
293:
294: =back
295:
296: Environment variables to be set for the command may also be passed
297: on the command line in the form of B<VAR>=I<value>, e.g.
298: B<LD_LIBRARY_PATH>=I</usr/local/pkg/lib>. Variables passed on the
299: command line are subject to the same restrictions as normal environment
300: variables with one important exception. If the I<setenv> option
301: is set in I<sudoers> or the command to be run has the C<SETENV> tag
302: set the user may set variables that would overwise be forbidden.
303: See L<sudoers(5)> for more information.
304:
305: =head1 RETURN VALUES
306:
307: Upon successful execution of a program, the return value from B<sudo>
308: will simply be the return value of the program that was executed.
309:
310: Otherwise, B<sudo> quits with an exit value of 1 if there is a
311: configuration/permission problem or if B<sudo> cannot execute the
312: given command. In the latter case the error string is printed to
313: stderr. If B<sudo> cannot L<stat(2)> one or more entries in the user's
314: C<PATH> an error is printed on stderr. (If the directory does not
315: exist or if it is not really a directory, the entry is ignored and
316: no error is printed.) This should not happen under normal
317: circumstances. The most common reason for L<stat(2)> to return
318: "permission denied" is if you are running an automounter and one
319: of the directories in your C<PATH> is on a machine that is currently
320: unreachable.
321:
322: =head1 SECURITY NOTES
323:
324: B<sudo> tries to be safe when executing external commands.
325:
326: There are two distinct ways to deal with environment variables.
327: By default, the I<env_reset> I<sudoers> option is enabled.
328: This causes commands to be executed with a minimal environment
329: containing C<TERM>, C<PATH>, C<HOME>, C<SHELL>, C<LOGNAME>, C<USER>
330: and C<USERNAME> in addition to variables from the invoking process
331: permitted by the I<env_check> and I<env_keep> I<sudoers> options.
332: There is effectively a whitelist for environment variables.
333:
334: If, however, the I<env_reset> option is disabled in I<sudoers>, any
335: variables not explicitly denied by the I<env_check> and I<env_delete>
336: options are inherited from the invoking process. In this case,
337: I<env_check> and I<env_delete> behave like a blacklist. Since it
338: is not possible to blacklist all potentially dangerous environment
339: variables, use of the default I<env_reset> behavior is encouraged.
340:
341: In all cases, environment variables with a value beginning with
342: C<()> are removed as they could be interpreted as B<bash> functions.
343: The list of environment variables that B<sudo> allows or denies is
344: contained in the output of C<sudo -V> when run as root.
345:
346: Note that the dynamic linker on most operating systems will remove
347: variables that can control dynamic linking from the environment of
348: setuid executables, including B<sudo>. Depending on the operating
349: system this may include C<_RLD*>, C<DYLD_*>, C<LD_*>, C<LDR_*>,
350: C<LIBPATH>, C<SHLIB_PATH>, and others. These type of variables are
351: removed from the environment before B<sudo> even begins execution
352: and, as such, it is not possible for B<sudo> to preserve them.
353:
354: To prevent command spoofing, B<sudo> checks "." and "" (both denoting
355: current directory) last when searching for a command in the user's
356: PATH (if one or both are in the PATH). Note, however, that the
357: actual C<PATH> environment variable is I<not> modified and is passed
358: unchanged to the program that B<sudo> executes.
359:
360: B<sudo> will check the ownership of its timestamp directory
361: (F<@timedir@> by default) and ignore the directory's contents if
362: it is not owned by root or if it is writable by a user other than
363: root. On systems that allow non-root users to give away files via
364: L<chown(2)>, if the timestamp directory is located in a directory
365: writable by anyone (e.g., F</tmp>), it is possible for a user to
366: create the timestamp directory before B<sudo> is run. However,
367: because B<sudo> checks the ownership and mode of the directory and
368: its contents, the only damage that can be done is to "hide" files
369: by putting them in the timestamp dir. This is unlikely to happen
370: since once the timestamp dir is owned by root and inaccessible by
371: any other user, the user placing files there would be unable to get
372: them back out. To get around this issue you can use a directory
373: that is not world-writable for the timestamps (F</var/adm/sudo> for
374: instance) or create F<@timedir@> with the appropriate owner (root)
375: and permissions (0700) in the system startup files.
376:
377: B<sudo> will not honor timestamps set far in the future.
378: Timestamps with a date greater than current_time + 2 * C<TIMEOUT>
379: will be ignored and sudo will log and complain. This is done to
380: keep a user from creating his/her own timestamp with a bogus
381: date on systems that allow users to give away files.
382:
383: Please note that B<sudo> will normally only log the command it
384: explicitly runs. If a user runs a command such as C<sudo su> or
385: C<sudo sh>, subsequent commands run from that shell will I<not> be
386: logged, nor will B<sudo>'s access control affect them. The same
387: is true for commands that offer shell escapes (including most
388: editors). Because of this, care must be taken when giving users
389: access to commands via B<sudo> to verify that the command does not
390: inadvertently give the user an effective root shell. For more
391: information, please see the C<PREVENTING SHELL ESCAPES> section in
392: L<sudoers(5)>.
393:
394: =head1 ENVIRONMENT
395:
396: B<sudo> utilizes the following environment variables:
397:
398: EDITOR Default editor to use in -e (sudoedit) mode if
399: VISUAL is not set
400:
401: HOME In -s or -H mode (or if sudo was configured with
402: the --enable-shell-sets-home option), set to
403: homedir of the target user
404:
405: PATH Set to a sane value if sudo was configured with
406: the --with-secure-path option
407:
408: SHELL Used to determine shell to run with -s option
409:
410: SUDO_PROMPT Used as the default password prompt
411:
412: SUDO_COMMAND Set to the command run by sudo
413:
414: SUDO_USER Set to the login of the user who invoked sudo
415:
416: SUDO_UID Set to the uid of the user who invoked sudo
417:
418: SUDO_GID Set to the gid of the user who invoked sudo
419:
420: SUDO_PS1 If set, PS1 will be set to its value
421:
422: USER Set to the target user (root unless the -u option
423: is specified)
424:
425: VISUAL Default editor to use in -e (sudoedit) mode
426:
427: =head1 FILES
428:
429: @sysconfdir@/sudoers List of who can run what
1.2 ! millert 430: @timedir@ Directory containing timestamps
1.1 millert 431:
432: =head1 EXAMPLES
433:
434: Note: the following examples assume suitable L<sudoers(5)> entries.
435:
436: To get a file listing of an unreadable directory:
437:
438: $ sudo ls /usr/local/protected
439:
440: To list the home directory of user yazza on a machine where the
441: file system holding ~yazza is not exported as root:
442:
443: $ sudo -u yazza ls ~yazza
444:
445: To edit the F<index.html> file as user www:
446:
447: $ sudo -u www vi ~www/htdocs/index.html
448:
449: To shutdown a machine:
450:
451: $ sudo shutdown -r +15 "quick reboot"
452:
453: To make a usage listing of the directories in the /home
454: partition. Note that this runs the commands in a sub-shell
455: to make the C<cd> and file redirection work.
456:
457: $ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
458:
459: =head1 SEE ALSO
460:
461: L<grep(1)>, L<su(1)>, L<stat(2)>, L<login_cap(3)>, L<passwd(5)>,
462: L<sudoers(5)>, L<visudo(8)>
463:
464: =head1 AUTHORS
465:
466: Many people have worked on B<sudo> over the years; this
467: version consists of code written primarily by:
468:
469: Todd C. Miller
470: Chris Jepeway
471:
472: See the HISTORY file in the B<sudo> distribution or visit
473: http://www.sudo.ws/sudo/history.html for a short history
474: of B<sudo>.
475:
476: =head1 CAVEATS
477:
478: There is no easy way to prevent a user from gaining a root shell
479: if that user is allowed to run arbitrary commands via B<sudo>.
480: Also, many programs (such as editors) allow the user to run commands
481: via shell escapes, thus avoiding B<sudo>'s checks. However, on
482: most systems it is possible to prevent shell escapes with B<sudo>'s
483: I<noexec> functionality. See the L<sudoers(5)> manual
484: for details.
485:
486: It is not meaningful to run the C<cd> command directly via sudo, e.g.,
487:
488: $ sudo cd /usr/local/protected
489:
490: since when the command exits the parent process (your shell) will
491: still be the same. Please see the EXAMPLES section for more information.
492:
493: If users have sudo C<ALL> there is nothing to prevent them from
494: creating their own program that gives them a root shell regardless
495: of any '!' elements in the user specification.
496:
497: Running shell scripts via B<sudo> can expose the same kernel bugs that
498: make setuid shell scripts unsafe on some operating systems (if your OS
499: has a /dev/fd/ directory, setuid shell scripts are generally safe).
500:
501: =head1 BUGS
502:
503: If you feel you have found a bug in B<sudo>, please submit a bug report
504: at http://www.sudo.ws/sudo/bugs/
505:
506: =head1 SUPPORT
507:
508: Limited free support is available via the sudo-users mailing list,
509: see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
510: search the archives.
511:
512: =head1 DISCLAIMER
513:
514: B<sudo> is provided ``AS IS'' and any express or implied warranties,
515: including, but not limited to, the implied warranties of merchantability
516: and fitness for a particular purpose are disclaimed. See the LICENSE
517: file distributed with B<sudo> or http://www.sudo.ws/sudo/license.html
518: for complete details.
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