1 Copyright (c) 1994-1996, 1998-2005, 2007-2010
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.
25 sudoers - list of which users may execute what
29 The I<sudoers> file is composed of two types of entries: aliases
30 (basically variables) and user specifications (which specify who
33 When multiple entries match for a user, they are applied in order.
34 Where there are multiple matches, the last match is used (which is
35 not necessarily the most specific match).
37 The I<sudoers> grammar will be described below in Extended Backus-Naur
38 Form (EBNF). Don't despair if you don't know what EBNF is; it is
39 fairly simple, and the definitions below are annotated.
41 =head2 Quick guide to EBNF
43 EBNF is a concise and exact way of describing the grammar of a language.
44 Each EBNF definition is made up of I<production rules>. E.g.,
46 symbol ::= definition | alternate1 | alternate2 ...
48 Each I<production rule> references others and thus makes up a
49 grammar for the language. EBNF also contains the following
50 operators, which many readers will recognize from regular
51 expressions. Do not, however, confuse them with "wildcard"
52 characters, which have different meanings.
58 Means that the preceding symbol (or group of symbols) is optional.
59 That is, it may appear once or not at all.
63 Means that the preceding symbol (or group of symbols) may appear
68 Means that the preceding symbol (or group of symbols) may appear
73 Parentheses may be used to group symbols together. For clarity,
74 we will use single quotes ('') to designate what is a verbatim character
75 string (as opposed to a symbol name).
79 There are four kinds of aliases: C<User_Alias>, C<Runas_Alias>,
80 C<Host_Alias> and C<Cmnd_Alias>.
82 Alias ::= 'User_Alias' User_Alias (':' User_Alias)* |
83 'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
84 'Host_Alias' Host_Alias (':' Host_Alias)* |
85 'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
87 User_Alias ::= NAME '=' User_List
89 Runas_Alias ::= NAME '=' Runas_List
91 Host_Alias ::= NAME '=' Host_List
93 Cmnd_Alias ::= NAME '=' Cmnd_List
95 NAME ::= [A-Z]([A-Z][0-9]_)*
97 Each I<alias> definition is of the form
99 Alias_Type NAME = item1, item2, ...
101 where I<Alias_Type> is one of C<User_Alias>, C<Runas_Alias>, C<Host_Alias>,
102 or C<Cmnd_Alias>. A C<NAME> is a string of uppercase letters, numbers,
103 and underscore characters ('_'). A C<NAME> B<must> start with an
104 uppercase letter. It is possible to put several alias definitions
105 of the same type on a single line, joined by a colon (':'). E.g.,
107 Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
109 The definitions of what constitutes a valid I<alias> member follow.
114 User ::= '!'* username |
118 '!'* '%:'nonunix_group |
121 A C<User_List> is made up of one or more usernames, uids (prefixed
122 with '#'), system groups (prefixed with '%'), netgroups (prefixed
123 with '+') and C<User_Alias>es. Each list item may be prefixed with
124 zero or more '!' operators. An odd number of '!' operators negate
125 the value of the item; an even number just cancel each other out.
127 A C<username>, C<group>, C<netgroup> and C<nonunix_groups> may
128 be enclosed in double quotes to avoid the need for escaping special
129 characters. Alternately, special characters may be specified in
130 escaped hex mode, e.g. \x20 for space.
132 The C<nonunix_group> syntax depends on the underlying implementation.
133 For instance, the QAS AD backend supports the following formats:
139 Group in the same domain: "Group Name"
143 Group in any domain: "Group Name@FULLY.QUALIFIED.DOMAIN"
147 Group SID: "S-1-2-34-5678901234-5678901234-5678901234-567"
151 Note that quotes around group names are optional. Unquoted strings must
152 use a backslash (\) to escape spaces and the '@' symbol.
154 Runas_List ::= Runas_Member |
155 Runas_Member ',' Runas_List
157 Runas_Member ::= '!'* username |
163 A C<Runas_List> is similar to a C<User_List> except that instead
164 of C<User_Alias>es it can contain C<Runas_Alias>es. Note that
165 usernames and groups are matched as strings. In other words, two
166 users (groups) with the same uid (gid) are considered to be distinct.
167 If you wish to match all usernames with the same uid (e.g.E<nbsp>root
168 and toor), you can use a uid instead (#0 in the example given).
173 Host ::= '!'* hostname |
175 '!'* network(/netmask)? |
179 A C<Host_List> is made up of one or more hostnames, IP addresses,
180 network numbers, netgroups (prefixed with '+') and other aliases.
181 Again, the value of an item may be negated with the '!' operator.
182 If you do not specify a netmask along with the network number,
183 B<sudo> will query each of the local host's network interfaces and,
184 if the network number corresponds to one of the hosts's network
185 interfaces, the corresponding netmask will be used. The netmask
186 may be specified either in standard IP address notation
187 (e.g.E<nbsp>255.255.255.0 or ffff:ffff:ffff:ffff::),
188 or CIDR notation (number of bits, e.g.E<nbsp>24 or 64). A hostname may
189 include shell-style wildcards (see the L<Wildcards> section below),
190 but unless the C<hostname> command on your machine returns the fully
191 qualified hostname, you'll need to use the I<fqdn> option for
192 wildcards to be useful.
197 commandname ::= filename |
201 Cmnd ::= '!'* commandname |
206 A C<Cmnd_List> is a list of one or more commandnames, directories, and other
207 aliases. A commandname is a fully qualified filename which may include
208 shell-style wildcards (see the L<Wildcards> section below). A simple
209 filename allows the user to run the command with any arguments he/she
210 wishes. However, you may also specify command line arguments (including
211 wildcards). Alternately, you can specify C<""> to indicate that the command
212 may only be run B<without> command line arguments. A directory is a
213 fully qualified pathname ending in a '/'. When you specify a directory
214 in a C<Cmnd_List>, the user will be able to run any file within that directory
215 (but not in any subdirectories therein).
217 If a C<Cmnd> has associated command line arguments, then the arguments
218 in the C<Cmnd> must match exactly those given by the user on the command line
219 (or match the wildcards if there are any). Note that the following
220 characters must be escaped with a '\' if they are used in command
221 arguments: ',', ':', '=', '\'. The special command C<"sudoedit">
222 is used to permit a user to run B<sudo> with the B<-e> option (or
223 as B<sudoedit>). It may take command line arguments just as
224 a normal command does.
228 Certain configuration options may be changed from their default
229 values at runtime via one or more C<Default_Entry> lines. These
230 may affect all users on any host, all users on a specific host, a
231 specific user, a specific command, or commands being run as a specific user.
232 Note that per-command entries may not include command line arguments.
233 If you need to specify arguments, define a C<Cmnd_Alias> and reference
236 Default_Type ::= 'Defaults' |
237 'Defaults' '@' Host_List |
238 'Defaults' ':' User_List |
239 'Defaults' '!' Cmnd_List |
240 'Defaults' '>' Runas_List
242 Default_Entry ::= Default_Type Parameter_List
244 Parameter_List ::= Parameter |
245 Parameter ',' Parameter_List
247 Parameter ::= Parameter '=' Value |
248 Parameter '+=' Value |
249 Parameter '-=' Value |
252 Parameters may be B<flags>, B<integer> values, B<strings>, or B<lists>.
253 Flags are implicitly boolean and can be turned off via the '!'
254 operator. Some integer, string and list parameters may also be
255 used in a boolean context to disable them. Values may be enclosed
256 in double quotes (C<">) when they contain multiple words. Special
257 characters may be escaped with a backslash (C<\>).
259 Lists have two additional assignment operators, C<+=> and C<-=>.
260 These operators are used to add to and delete from a list respectively.
261 It is not an error to use the C<-=> operator to remove an element
262 that does not exist in a list.
264 Defaults entries are parsed in the following order: generic, host
265 and user Defaults first, then runas Defaults and finally command
268 See L<"SUDOERS OPTIONS"> for a list of supported Defaults parameters.
270 =head2 User Specification
272 User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
273 (':' Host_List '=' Cmnd_Spec_List)*
275 Cmnd_Spec_List ::= Cmnd_Spec |
276 Cmnd_Spec ',' Cmnd_Spec_List
278 Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd
280 Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
282 Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |
283 'SETENV:' | 'NOSETENV:' )
285 A B<user specification> determines which commands a user may run
286 (and as what user) on specified hosts. By default, commands are
287 run as B<root>, but this can be changed on a per-command basis.
289 The basic structure of a user specification is `who = where (as_whom)
290 what'. Let's break that down into its constituent parts:
294 A C<Runas_Spec> determines the user and/or the group that a command
295 may be run as. A fully-specified C<Runas_Spec> consists of two
296 C<Runas_List>s (as defined above) separated by a colon (':') and
297 enclosed in a set of parentheses. The first C<Runas_List> indicates
298 which users the command may be run as via B<sudo>'s B<-u> option.
299 The second defines a list of groups that can be specified via
300 B<sudo>'s B<-g> option. If both C<Runas_List>s are specified, the
301 command may be run with any combination of users and groups listed
302 in their respective C<Runas_List>s. If only the first is specified,
303 the command may be run as any user in the list but no B<-g> option
304 may be specified. If the first C<Runas_List> is empty but the
305 second is specified, the command may be run as the invoking user
306 with the group set to any listed in the C<Runas_List>. If no
307 C<Runas_Spec> is specified the command may be run as B<root> and
308 no group may be specified.
310 A C<Runas_Spec> sets the default for the commands that follow it.
311 What this means is that for the entry:
313 dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
315 The user B<dgb> may run F</bin/ls>, F</bin/kill>, and
316 F</usr/bin/lprm> -- but only as B<operator>. E.g.,
318 $ sudo -u operator /bin/ls.
320 It is also possible to override a C<Runas_Spec> later on in an
321 entry. If we modify the entry like so:
323 dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
325 Then user B<dgb> is now allowed to run F</bin/ls> as B<operator>,
326 but F</bin/kill> and F</usr/bin/lprm> as B<root>.
328 We can extend this to allow B<dgb> to run C</bin/ls> with either
329 the user or group set to B<operator>:
331 dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \
334 In the following example, user B<tcm> may run commands that access
335 a modem device file with the dialer group. Note that in this example
336 only the group will be set, the command still runs as user B<tcm>.
338 tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \
339 /usr/local/bin/minicom
343 A command may have zero or more tags associated with it. There are
344 eight possible tag values, C<NOPASSWD>, C<PASSWD>, C<NOEXEC>, C<EXEC>,
345 C<SETENV> and C<NOSETENV>.
346 Once a tag is set on a C<Cmnd>, subsequent C<Cmnd>s in the
347 C<Cmnd_Spec_List>, inherit the tag unless it is overridden by the
348 opposite tag (i.e.: C<PASSWD> overrides C<NOPASSWD> and C<NOEXEC>
351 =head3 NOPASSWD and PASSWD
353 By default, B<sudo> requires that a user authenticate him or herself
354 before running a command. This behavior can be modified via the
355 C<NOPASSWD> tag. Like a C<Runas_Spec>, the C<NOPASSWD> tag sets
356 a default for the commands that follow it in the C<Cmnd_Spec_List>.
357 Conversely, the C<PASSWD> tag can be used to reverse things.
360 ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
362 would allow the user B<ray> to run F</bin/kill>, F</bin/ls>, and
363 F</usr/bin/lprm> as B<root> on the machine rushmore without
364 authenticating himself. If we only want B<ray> to be able to
365 run F</bin/kill> without a password the entry would be:
367 ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
369 Note, however, that the C<PASSWD> tag has no effect on users who are
370 in the group specified by the I<exempt_group> option.
372 By default, if the C<NOPASSWD> tag is applied to any of the entries
373 for a user on the current host, he or she will be able to run
374 C<sudo -l> without a password. Additionally, a user may only run
375 C<sudo -v> without a password if the C<NOPASSWD> tag is present
376 for all a user's entries that pertain to the current host.
377 This behavior may be overridden via the verifypw and listpw options.
379 =head3 NOEXEC and EXEC
381 If B<sudo> has been compiled with I<noexec> support and the underlying
382 operating system supports it, the C<NOEXEC> tag can be used to prevent
383 a dynamically-linked executable from running further commands itself.
385 In the following example, user B<aaron> may run F</usr/bin/more>
386 and F</usr/bin/vi> but shell escapes will be disabled.
388 aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
390 See the L<PREVENTING SHELL ESCAPES> section below for more details
391 on how C<NOEXEC> works and whether or not it will work on your system.
393 =head3 SETENV and NOSETENV
395 These tags override the value of the I<setenv> option on a per-command
396 basis. Note that if C<SETENV> has been set for a command, any
397 environment variables set on the command line way are not subject
398 to the restrictions imposed by I<env_check>, I<env_delete>, or
399 I<env_keep>. As such, only trusted users should be allowed to set
400 variables in this manner. If the command matched is B<ALL>, the
401 C<SETENV> tag is implied for that command; this default may
402 be overridden by use of the C<UNSETENV> tag.
406 B<sudo> allows shell-style I<wildcards> (aka meta or glob characters)
407 to be used in hostnames, pathnames and command line arguments in
408 the I<sudoers> file. Wildcard matching is done via the B<POSIX>
409 L<glob(3)> and L<fnmatch(3)> routines. Note that these are I<not>
416 Matches any set of zero or more characters.
420 Matches any single character.
424 Matches any character in the specified range.
428 Matches any character B<not> in the specified range.
432 For any character "x", evaluates to "x". This is used to
433 escape special characters such as: "*", "?", "[", and "}".
437 POSIX character classes may also be used if your system's L<glob(3)>
438 and L<fnmatch(3)> functions support them. However, because the
439 C<':'> character has special meaning in I<sudoers>, it must be
440 escaped. For example:
442 /bin/ls [[\:alpha\:]]*
444 Would match any filename beginning with a letter.
446 Note that a forward slash ('/') will B<not> be matched by
447 wildcards used in the pathname. When matching the command
448 line arguments, however, a slash B<does> get matched by
449 wildcards. This is to make a path like:
453 match F</usr/bin/who> but not F</usr/bin/X11/xterm>.
455 =head2 Exceptions to wildcard rules
457 The following exceptions apply to the above rules:
463 If the empty string C<""> is the only command line argument in the
464 I<sudoers> entry it means that command is not allowed to be run
465 with B<any> arguments.
469 =head2 Including other files from within sudoers
471 It is possible to include other I<sudoers> files from within the
472 I<sudoers> file currently being parsed using the C<#include> and
473 C<#includedir> directives.
475 This can be used, for example, to keep a site-wide I<sudoers> file
476 in addition to a local, per-machine file. For the sake of this
477 example the site-wide I<sudoers> will be F</etc/sudoers> and the
478 per-machine one will be F</etc/sudoers.local>. To include
479 F</etc/sudoers.local> from within F</etc/sudoers> we would use the
480 following line in F</etc/sudoers>:
484 C<#include /etc/sudoers.local>
488 When B<sudo> reaches this line it will suspend processing of the
489 current file (F</etc/sudoers>) and switch to F</etc/sudoers.local>.
490 Upon reaching the end of F</etc/sudoers.local>, the rest of
491 F</etc/sudoers> will be processed. Files that are included may
492 themselves include other files. A hard limit of 128 nested include
493 files is enforced to prevent include file loops.
495 The filename may include the C<%h> escape, signifying the short form
496 of the hostname. I.e., if the machine's hostname is "xerxes", then
498 C<#include /etc/sudoers.%h>
500 will cause B<sudo> to include the file F</etc/sudoers.xerxes>.
502 The C<#includedir> directive can be used to create a F<sudo.d>
503 directory that the system package manager can drop I<sudoers> rules
504 into as part of package installation. For example, given:
506 C<#includedir /etc/sudoers.d>
508 B<sudo> will read each file in F</etc/sudoers.d>, skipping file
509 names that end in C<~> or contain a C<.> character to avoid causing
510 problems with package manager or editor temporary/backup files.
511 Files are parsed in sorted lexical order. That is,
512 F</etc/sudoers.d/01_first> will be parsed before
513 F</etc/sudoers.d/10_second>. Be aware that because the sorting is
514 lexical, not numeric, F</etc/sudoers.d/1_whoops> would be loaded
515 B<after> F</etc/sudoers.d/10_second>. Using a consistent number
516 of leading zeroes in the file names can be used to avoid such
519 Note that unlike files included via C<#include>, B<visudo> will not
520 edit the files in a C<#includedir> directory unless one of them
521 contains a syntax error. It is still possible to run B<visudo>
522 with the C<-f> flag to edit the files directly.
524 =head2 Other special characters and reserved words
526 The pound sign ('#') is used to indicate a comment (unless it is
527 part of a #include directive or unless it occurs in the context of
528 a user name and is followed by one or more digits, in which case
529 it is treated as a uid). Both the comment character and any text
530 after it, up to the end of the line, are ignored.
532 The reserved word B<ALL> is a built-in I<alias> that always causes
533 a match to succeed. It can be used wherever one might otherwise
534 use a C<Cmnd_Alias>, C<User_Alias>, C<Runas_Alias>, or C<Host_Alias>.
535 You should not try to define your own I<alias> called B<ALL> as the
536 built-in alias will be used in preference to your own. Please note
537 that using B<ALL> can be dangerous since in a command context, it
538 allows the user to run B<any> command on the system.
540 An exclamation point ('!') can be used as a logical I<not> operator
541 both in an I<alias> and in front of a C<Cmnd>. This allows one to
542 exclude certain values. Note, however, that using a C<!> in
543 conjunction with the built-in C<ALL> alias to allow a user to
544 run "all but a few" commands rarely works as intended (see SECURITY
547 Long lines can be continued with a backslash ('\') as the last
548 character on the line.
550 Whitespace between elements in a list as well as special syntactic
551 characters in a I<User Specification> ('=', ':', '(', ')') is optional.
553 The following characters must be escaped with a backslash ('\') when
554 used as part of a word (e.g.E<nbsp>a username or hostname):
555 '@', '!', '=', ':', ',', '(', ')', '\'.
557 =head1 SUDOERS OPTIONS
559 B<sudo>'s behavior can be modified by C<Default_Entry> lines, as
560 explained earlier. A list of all supported Defaults parameters,
561 grouped by type, are listed below.
567 =item always_set_home
569 If set, B<sudo> will set the C<HOME> environment variable to the home
570 directory of the target user (which is root unless the B<-u> option is used).
571 This effectively means that the B<-H> option is always implied.
572 This flag is I<off> by default.
576 If set, users must authenticate themselves via a password (or other
577 means of authentication) before they may run commands. This default
578 may be overridden via the C<PASSWD> and C<NOPASSWD> tags.
579 This flag is I<on> by default.
581 =item closefrom_override
583 If set, the user may use B<sudo>'s B<-C> option which
584 overrides the default starting point at which B<sudo> begins
585 closing open file descriptors. This flag is I<off> by default.
589 If set, B<visudo> will use the value of the EDITOR or VISUAL
590 environment variables before falling back on the default editor list.
591 Note that this may create a security hole as it allows the user to
592 run any arbitrary command as root without logging. A safer alternative
593 is to place a colon-separated list of editors in the C<editor>
594 variable. B<visudo> will then only use the EDITOR or VISUAL if
595 they match a value specified in C<editor>. This flag is I<@env_editor@> by
600 If set, B<sudo> will reset the environment to only contain the
601 LOGNAME, SHELL, USER, USERNAME and the C<SUDO_*> variables. Any
602 variables in the caller's environment that match the C<env_keep>
603 and C<env_check> lists are then added. The default contents of the
604 C<env_keep> and C<env_check> lists are displayed when B<sudo> is
605 run by root with the I<-V> option. If the I<secure_path> option
606 is set, its value will be used for the C<PATH> environment variable.
607 This flag is I<on> by default.
611 Set this flag if you want to put fully qualified hostnames in the
612 I<sudoers> file. I.e., instead of myhost you would use myhost.mydomain.edu.
613 You may still use the short form if you wish (and even mix the two).
614 Beware that turning on I<fqdn> requires B<sudo> to make DNS lookups
615 which may make B<sudo> unusable if DNS stops working (for example
616 if the machine is not plugged into the network). Also note that
617 you must use the host's official name as DNS knows it. That is,
618 you may not use a host alias (C<CNAME> entry) due to performance
619 issues and the fact that there is no way to get all aliases from
620 DNS. If your machine's hostname (as returned by the C<hostname>
621 command) is already fully qualified you shouldn't need to set
622 I<fqdn>. This flag is I<@fqdn@> by default.
626 If set, B<sudo> will ignore '.' or '' (current dir) in the C<PATH>
627 environment variable; the C<PATH> itself is not modified. This
628 flag is I<@ignore_dot@> by default.
630 =item ignore_local_sudoers
632 If set via LDAP, parsing of F<@sysconfdir@/sudoers> will be skipped.
633 This is intended for Enterprises that wish to prevent the usage of local
634 sudoers files so that only LDAP is used. This thwarts the efforts of
635 rogue operators who would attempt to add roles to F<@sysconfdir@/sudoers>.
636 When this option is present, F<@sysconfdir@/sudoers> does not even need to
637 exist. Since this option tells B<sudo> how to behave when no specific LDAP
638 entries have been matched, this sudoOption is only meaningful for the
639 C<cn=defaults> section. This flag is I<off> by default.
643 If set, B<sudo> will insult users when they enter an incorrect
644 password. This flag is I<@insults@> by default.
648 If set, the hostname will be logged in the (non-syslog) B<sudo> log file.
649 This flag is I<off> by default.
653 If set, the four-digit year will be logged in the (non-syslog) B<sudo> log file.
654 This flag is I<off> by default.
656 =item long_otp_prompt
658 When validating with a One Time Password (OPT) scheme such as
659 B<S/Key> or B<OPIE>, a two-line prompt is used to make it easier
660 to cut and paste the challenge to a local window. It's not as
661 pretty as the default but some people find it more convenient. This
662 flag is I<@long_otp_prompt@> by default.
666 Send mail to the I<mailto> user every time a users runs B<sudo>.
667 This flag is I<off> by default.
671 Send mail to the I<mailto> user if the user running B<sudo> does not
672 enter the correct password. This flag is I<off> by default.
676 If set, mail will be sent to the I<mailto> user if the invoking
677 user exists in the I<sudoers> file, but is not allowed to run
678 commands on the current host. This flag is I<@mail_no_host@> by default.
682 If set, mail will be sent to the I<mailto> user if the invoking
683 user is allowed to use B<sudo> but the command they are trying is not
684 listed in their I<sudoers> file entry or is explicitly denied.
685 This flag is I<@mail_no_perms@> by default.
689 If set, mail will be sent to the I<mailto> user if the invoking
690 user is not in the I<sudoers> file. This flag is I<@mail_no_user@>
695 If set, all commands run via B<sudo> will behave as if the C<NOEXEC>
696 tag has been set, unless overridden by a C<EXEC> tag. See the
697 description of I<NOEXEC and EXEC> below as well as the L<PREVENTING SHELL
698 ESCAPES> section at the end of this manual. This flag is I<off> by default.
702 Normally, B<sudo> will tell the user when a command could not be
703 found in their C<PATH> environment variable. Some sites may wish
704 to disable this as it could be used to gather information on the
705 location of executables that the normal user does not have access
706 to. The disadvantage is that if the executable is simply not in
707 the user's C<PATH>, B<sudo> will tell the user that they are not
708 allowed to run it, which can be confusing. This flag is I<@path_info@>
711 =item passprompt_override
713 The password prompt specified by I<passprompt> will normally only
714 be used if the passwod prompt provided by systems such as PAM matches
715 the string "Password:". If I<passprompt_override> is set, I<passprompt>
716 will always be used. This flag is I<off> by default.
718 =item preserve_groups
720 By default, B<sudo> will initialize the group vector to the list of
721 groups the target user is in. When I<preserve_groups> is set, the
722 user's existing group vector is left unaltered. The real and
723 effective group IDs, however, are still set to match the target
724 user. This flag is I<off> by default.
728 By default, B<sudo> reads the password like most other Unix programs,
729 by turning off echo until the user hits the return (or enter) key.
730 Some users become confused by this as it appears to them that B<sudo>
731 has hung at this point. When I<pwfeedback> is set, B<sudo> will
732 provide visual feedback when the user presses a key. Note that
733 this does have a security impact as an onlooker may be able to
734 determine the length of the password being entered.
735 This flag is I<off> by default.
739 If set, B<sudo> will only run when the user is logged in to a real
740 tty. When this flag is set, B<sudo> can only be run from a login
741 session and not via other means such as L<cron(8)> or cgi-bin scripts.
742 This flag is I<off> by default.
746 If set, root is allowed to run B<sudo> too. Disabling this prevents users
747 from "chaining" B<sudo> commands to get a root shell by doing something
748 like C<"sudo sudo /bin/sh">. Note, however, that turning off I<root_sudo>
749 will also prevent root and from running B<sudoedit>.
750 Disabling I<root_sudo> provides no real additional security; it
751 exists purely for historical reasons.
752 This flag is I<@root_sudo@> by default.
756 If set, B<sudo> will prompt for the root password instead of the password
757 of the invoking user. This flag is I<off> by default.
761 If set, B<sudo> will prompt for the password of the user defined by the
762 I<runas_default> option (defaults to C<@runas_default@>) instead of the
763 password of the invoking user. This flag is I<off> by default.
767 If set and B<sudo> is invoked with the B<-s> option the C<HOME>
768 environment variable will be set to the home directory of the target
769 user (which is root unless the B<-u> option is used). This effectively
770 makes the B<-s> option imply B<-H>. This flag is I<off> by default.
774 Normally, B<sudo> will set the C<LOGNAME>, C<USER> and C<USERNAME>
775 environment variables to the name of the target user (usually root
776 unless the B<-u> option is given). However, since some programs
777 (including the RCS revision control system) use C<LOGNAME> to
778 determine the real identity of the user, it may be desirable to
779 change this behavior. This can be done by negating the set_logname
780 option. Note that if the I<env_reset> option has not been disabled,
781 entries in the I<env_keep> list will override the value of
782 I<set_logname>. This flag is I<off> by default.
786 Allow the user to disable the I<env_reset> option from the command
787 line. Additionally, environment variables set via the command line
788 are not subject to the restrictions imposed by I<env_check>,
789 I<env_delete>, or I<env_keep>. As such, only trusted users should
790 be allowed to set variables in this manner. This flag is I<off>
795 If set and B<sudo> is invoked with no arguments it acts as if the
796 B<-s> option had been given. That is, it runs a shell as root (the
797 shell is determined by the C<SHELL> environment variable if it is
798 set, falling back on the shell listed in the invoking user's
799 /etc/passwd entry if not). This flag is I<off> by default.
803 Normally, B<sudo> uses the L<glob(3)> function to do shell-style
804 globbing when matching pathnames. However, since it accesses the
805 file system, L<glob(3)> can take a long time to complete for some
806 patterns, especially when the pattern references a network file
807 system that is mounted on demand (automounted). The I<fast_glob>
808 option causes B<sudo> to use the L<fnmatch(3)> function, which does
809 not access the file system to do its matching. The disadvantage
810 of I<fast_glob> is that it is unable to match relative pathnames
811 such as F<./ls> or F<../bin/ls>. This has security implications
812 when path names that include globbing characters are used with the
813 negation operator, C<'!'>, as such rules can be trivially bypassed.
814 As such, this option should not be used when I<sudoers> contains rules
815 that contain negated path names which include globbing characters.
816 This flag is I<off> by default.
820 Normally, when B<sudo> executes a command the real and effective
821 UIDs are set to the target user (root by default). This option
822 changes that behavior such that the real UID is left as the invoking
823 user's UID. In other words, this makes B<sudo> act as a setuid
824 wrapper. This can be useful on systems that disable some potentially
825 dangerous functionality when a program is run setuid. This option
826 is only effective on systems with either the setreuid() or setresuid()
827 function. This flag is I<off> by default.
831 If set, B<sudo> will prompt for the password of the user specified by
832 the B<-u> option (defaults to C<root>) instead of the password of the
833 invoking user. Note that this precludes the use of a uid not listed
834 in the passwd database as an argument to the B<-u> option.
835 This flag is I<off> by default.
839 If set, users must authenticate on a per-tty basis. Normally,
840 B<sudo> uses a directory in the ticket dir with the same name as
841 the user running it. With this flag enabled, B<sudo> will use a
842 file named for the tty the user is logged in on in that directory.
843 This flag is I<@tty_tickets@> by default.
847 If set, B<sudo> will set the umask as specified by I<sudoers> without
848 modification. This makes it possible to specify a more permissive
849 umask in I<sudoers> than the user's own umask and matches historical
850 behavior. If I<umask_override> is not set, B<sudo> will set the
851 umask to be the union of the user's umask and what is specified in
852 I<sudoers>. This flag is I<off> by default.
856 If set, B<sudo> will apply the defaults specified for the target user's
857 login class if one exists. Only available if B<sudo> is configured with
858 the --with-logincap option. This flag is I<off> by default.
862 By default, B<sudo> will refuse to run if the user must enter a
863 password but it is not possible to disable echo on the terminal.
864 If the I<visiblepw> flag is set, B<sudo> will prompt for a password
865 even when it would be visible on the screen. This makes it possible
866 to run things like C<"rsh somehost sudo ls"> since L<rsh(1)> does
867 not allocate a tty. This flag is I<off> by default.
877 Before it executes a command, B<sudo> will close all open file
878 descriptors other than standard input, standard output and standard
879 error (ie: file descriptors 0-2). The I<closefrom> option can be used
880 to specify a different file descriptor at which to start closing.
885 The number of tries a user gets to enter his/her password before
886 B<sudo> logs the failure and exits. The default is C<@passwd_tries@>.
890 B<Integers that can be used in a boolean context>:
896 Number of characters per line for the file log. This value is used
897 to decide when to wrap lines for nicer log files. This has no
898 effect on the syslog log file, only the file log. The default is
899 C<@loglen@> (use 0 or negate the option to disable word wrap).
903 Number of minutes before the B<sudo> password prompt times out.
904 The default is C<@password_timeout@>; set this to C<0> for no password timeout.
906 =item timestamp_timeout
908 Number of minutes that can elapse before B<sudo> will ask for a
909 passwd again. The default is C<@timeout@>. Set this to C<0> to always
910 prompt for a password.
911 If set to a value less than C<0> the user's timestamp will never
912 expire. This can be used to allow users to create or delete their
913 own timestamps via C<sudo -v> and C<sudo -k> respectively.
917 Umask to use when running the command. Negate this option or set
918 it to 0777 to preserve the user's umask. The actual umask that is
919 used will be the union of the user's umask and C<@sudo_umask@>.
920 This guarantees that B<sudo> never lowers the umask when running a
921 command. Note on systems that use PAM, the default PAM configuration
922 may specify its own umask which will override the value set in
931 =item badpass_message
933 Message that is displayed if a user enters an incorrect password.
934 The default is C<@badpass_message@> unless insults are enabled.
938 A colon (':') separated list of editors allowed to be used with
939 B<visudo>. B<visudo> will choose the editor that matches the user's
940 EDITOR environment variable if possible, or the first editor in the
941 list that exists and is executable. The default is the path to vi
946 Subject of the mail sent to the I<mailto> user. The escape C<%h>
947 will expand to the hostname of the machine.
948 Default is C<@mailsub@>.
952 Path to a shared library containing dummy versions of the execv(),
953 execve() and fexecve() library functions that just return an error.
954 This is used to implement the I<noexec> functionality on systems that
955 support C<LD_PRELOAD> or its equivalent. Defaults to F<@noexec_file@>.
959 The default prompt to use when asking for a password; can be overridden
960 via the B<-p> option or the C<SUDO_PROMPT> environment variable.
961 The following percent (`C<%>') escapes are supported:
967 expanded to the local hostname including the domain name
968 (on if the machine's hostname is fully qualified or the I<fqdn>
973 expanded to the local hostname without the domain name
977 expanded to the user whose password is being asked for (respects the
978 I<rootpw>, I<targetpw> and I<runaspw> flags in I<sudoers>)
982 expanded to the login name of the user the command will
983 be run as (defaults to root)
987 expanded to the invoking user's login name
991 two consecutive C<%> characters are collapsed into a single C<%> character
995 The default value is C<@passprompt@>.
999 The default SELinux role to use when constructing a new security
1000 context to run the command. The default role may be overridden on
1001 a per-command basis in I<sudoers> or via command line options.
1002 This option is only available whe B<sudo> is built with SELinux support.
1006 The default user to run commands as if the B<-u> option is not specified
1007 on the command line. This defaults to C<@runas_default@>.
1008 Note that if I<runas_default> is set it B<must> occur before
1009 any C<Runas_Alias> specifications.
1013 Syslog priority to use when user authenticates unsuccessfully.
1014 Defaults to C<@badpri@>.
1016 =item syslog_goodpri
1018 Syslog priority to use when user authenticates successfully.
1019 Defaults to C<@goodpri@>.
1021 =item sudoers_locale
1023 Locale to use when parsing the sudoers file. Note that changing
1024 the locale may affect how sudoers is interpreted.
1029 The directory in which B<sudo> stores its timestamp files.
1030 The default is F<@timedir@>.
1032 =item timestampowner
1034 The owner of the timestamp directory and the timestamps stored therein.
1035 The default is C<root>.
1039 The default SELinux type to use when constructing a new security
1040 context to run the command. The default type may be overridden on
1041 a per-command basis in I<sudoers> or via command line options.
1042 This option is only available whe B<sudo> is built with SELinux support.
1046 B<Strings that can be used in a boolean context>:
1052 The I<askpass> option specifies the fully qualified path to a helper
1053 program used to read the user's password when no terminal is
1054 available. This may be the case when B<sudo> is executed from a
1055 graphical (as opposed to text-based) application. The program
1056 specified by I<askpass> should display the argument passed to it
1057 as the prompt and write the user's password to the standard output.
1058 The value of I<askpass> may be overridden by the C<SUDO_ASKPASS>
1059 environment variable.
1063 The I<env_file> options specifies the fully qualified path to a
1064 file containing variables to be set in the environment of the program
1065 being run. Entries in this file should either be of the form
1066 C<VARIABLE=value> or C<export VARIABLE=value>. The value may
1067 optionally be surrounded by single or double quotes. Variables in
1068 this file are subject to other B<sudo> environment settings such
1069 as I<env_keep> and I<env_check>.
1073 Users in this group are exempt from password and PATH requirements.
1074 This is not set by default.
1078 This option controls when a short lecture will be printed along with
1079 the password prompt. It has the following possible values:
1085 Always lecture the user.
1089 Never lecture the user.
1093 Only lecture the user the first time they run B<sudo>.
1097 If no value is specified, a value of I<once> is implied.
1098 Negating the option results in a value of I<never> being used.
1099 The default value is I<@lecture@>.
1103 Path to a file containing an alternate B<sudo> lecture that will
1104 be used in place of the standard lecture if the named file exists.
1105 By default, B<sudo> uses a built-in lecture.
1109 This option controls when a password will be required when a
1110 user runs B<sudo> with the B<-l> option. It has the following possible values:
1116 All the user's I<sudoers> entries for the current host must have
1117 the C<NOPASSWD> flag set to avoid entering a password.
1121 The user must always enter a password to use the B<-l> option.
1125 At least one of the user's I<sudoers> entries for the current host
1126 must have the C<NOPASSWD> flag set to avoid entering a password.
1130 The user need never enter a password to use the B<-l> option.
1134 If no value is specified, a value of I<any> is implied.
1135 Negating the option results in a value of I<never> being used.
1136 The default value is I<any>.
1140 Path to the B<sudo> log file (not the syslog log file). Setting a path
1141 turns on logging to a file; negating this option turns it off.
1142 By default, B<sudo> logs via syslog.
1146 Flags to use when invoking mailer. Defaults to B<-t>.
1150 Path to mail program used to send warning mail.
1151 Defaults to the path to sendmail found at configure time.
1155 Address to use for the "from" address when sending warning and error
1156 mail. The address should be enclosed in double quotes (C<">) to
1157 protect against B<sudo> interpreting the C<@> sign. Defaults to
1158 the name of the user running B<sudo>.
1162 Address to send warning and error mail to. The address should
1163 be enclosed in double quotes (C<">) to protect against B<sudo>
1164 interpreting the C<@> sign. Defaults to C<@mailto@>.
1168 Path used for every command run from B<sudo>. If you don't trust the
1169 people running B<sudo> to have a sane C<PATH> environment variable you may
1170 want to use this. Another use is if you want to have the "root path"
1171 be separate from the "user path." Users in the group specified by the
1172 I<exempt_group> option are not affected by I<secure_path>.
1173 This option is @secure_path@ by default.
1177 Syslog facility if syslog is being used for logging (negate to
1178 disable syslog logging). Defaults to C<@logfac@>.
1182 This option controls when a password will be required when a user runs
1183 B<sudo> with the B<-v> option. It has the following possible values:
1189 All the user's I<sudoers> entries for the current host must have
1190 the C<NOPASSWD> flag set to avoid entering a password.
1194 The user must always enter a password to use the B<-v> option.
1198 At least one of the user's I<sudoers> entries for the current host
1199 must have the C<NOPASSWD> flag set to avoid entering a password.
1203 The user need never enter a password to use the B<-v> option.
1207 If no value is specified, a value of I<all> is implied.
1208 Negating the option results in a value of I<never> being used.
1209 The default value is I<all>.
1213 B<Lists that can be used in a boolean context>:
1219 Environment variables to be removed from the user's environment if
1220 the variable's value contains C<%> or C</> characters. This can
1221 be used to guard against printf-style format vulnerabilities in
1222 poorly-written programs. The argument may be a double-quoted,
1223 space-separated list or a single value without double-quotes. The
1224 list can be replaced, added to, deleted from, or disabled by using
1225 the C<=>, C<+=>, C<-=>, and C<!> operators respectively. Regardless
1226 of whether the C<env_reset> option is enabled or disabled, variables
1227 specified by C<env_check> will be preserved in the environment if
1228 they pass the aforementioned check. The default list of environment
1229 variables to check is displayed when B<sudo> is run by root with
1234 Environment variables to be removed from the user's environment
1235 when the I<env_reset> option is not in effect. The argument may
1236 be a double-quoted, space-separated list or a single value without
1237 double-quotes. The list can be replaced, added to, deleted from,
1238 or disabled by using the C<=>, C<+=>, C<-=>, and C<!> operators
1239 respectively. The default list of environment variables to remove
1240 is displayed when B<sudo> is run by root with the I<-V> option.
1241 Note that many operating systems will remove potentially dangerous
1242 variables from the environment of any setuid process (such as
1247 Environment variables to be preserved in the user's environment
1248 when the I<env_reset> option is in effect. This allows fine-grained
1249 control over the environment B<sudo>-spawned processes will receive.
1250 The argument may be a double-quoted, space-separated list or a
1251 single value without double-quotes. The list can be replaced, added
1252 to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and
1253 C<!> operators respectively. The default list of variables to keep
1254 is displayed when B<sudo> is run by root with the I<-V> option.
1258 When logging via L<syslog(3)>, B<sudo> accepts the following values
1259 for the syslog facility (the value of the B<syslog> Parameter):
1260 B<authpriv> (if your OS supports it), B<auth>, B<daemon>, B<user>,
1261 B<local0>, B<local1>, B<local2>, B<local3>, B<local4>, B<local5>,
1262 B<local6>, and B<local7>. The following syslog priorities are
1263 supported: B<alert>, B<crit>, B<debug>, B<emerg>, B<err>, B<info>,
1264 B<notice>, and B<warning>.
1270 =item F<@sysconfdir@/sudoers>
1272 List of who can run what
1278 =item F</etc/netgroup>
1280 List of network groups
1286 Below are example I<sudoers> entries. Admittedly, some of
1287 these are a bit contrived. First, we define our I<aliases>:
1289 # User alias specification
1290 User_Alias FULLTIMERS = millert, mikef, dowdy
1291 User_Alias PARTTIMERS = bostley, jwfox, crawl
1292 User_Alias WEBMASTERS = will, wendy, wim
1294 # Runas alias specification
1295 Runas_Alias OP = root, operator
1296 Runas_Alias DB = oracle, sybase
1297 Runas_Alias ADMINGRP = adm, oper
1299 # Host alias specification
1300 Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
1301 SGI = grolsch, dandelion, black :\
1302 ALPHA = widget, thalamus, foobar :\
1303 HPPA = boa, nag, python
1304 Host_Alias CUNETS = 128.138.0.0/255.255.0.0
1305 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
1306 Host_Alias SERVERS = master, mail, www, ns
1307 Host_Alias CDROM = orion, perseus, hercules
1309 # Cmnd alias specification
1310 Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
1311 /usr/sbin/restore, /usr/sbin/rrestore
1312 Cmnd_Alias KILL = /usr/bin/kill
1313 Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
1314 Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
1315 Cmnd_Alias HALT = /usr/sbin/halt
1316 Cmnd_Alias REBOOT = /usr/sbin/reboot
1317 Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
1318 /usr/local/bin/tcsh, /usr/bin/rsh, \
1320 Cmnd_Alias SU = /usr/bin/su
1321 Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
1323 Here we override some of the compiled in default values. We want
1324 B<sudo> to log via L<syslog(3)> using the I<auth> facility in all
1325 cases. We don't want to subject the full time staff to the B<sudo>
1326 lecture, user B<millert> need not give a password, and we don't
1327 want to reset the C<LOGNAME>, C<USER> or C<USERNAME> environment
1328 variables when running commands as root. Additionally, on the
1329 machines in the I<SERVERS> C<Host_Alias>, we keep an additional
1330 local log file and make sure we log the year in each log line since
1331 the log entries will be kept around for several years. Lastly, we
1332 disable shell escapes for the commands in the PAGERS C<Cmnd_Alias>
1333 (F</usr/bin/more>, F</usr/bin/pg> and F</usr/bin/less>).
1335 # Override built-in defaults
1336 Defaults syslog=auth
1337 Defaults>root !set_logname
1338 Defaults:FULLTIMERS !lecture
1339 Defaults:millert !authenticate
1340 Defaults@SERVERS log_year, logfile=/var/log/sudo.log
1341 Defaults!PAGERS noexec
1343 The I<User specification> is the part that actually determines who may
1346 root ALL = (ALL) ALL
1347 %wheel ALL = (ALL) ALL
1349 We let B<root> and any user in group B<wheel> run any command on any
1352 FULLTIMERS ALL = NOPASSWD: ALL
1354 Full time sysadmins (B<millert>, B<mikef>, and B<dowdy>) may run any
1355 command on any host without authenticating themselves.
1357 PARTTIMERS ALL = ALL
1359 Part time sysadmins (B<bostley>, B<jwfox>, and B<crawl>) may run any
1360 command on any host but they must authenticate themselves first
1361 (since the entry lacks the C<NOPASSWD> tag).
1365 The user B<jack> may run any command on the machines in the I<CSNETS> alias
1366 (the networks C<128.138.243.0>, C<128.138.204.0>, and C<128.138.242.0>).
1367 Of those networks, only C<128.138.204.0> has an explicit netmask (in
1368 CIDR notation) indicating it is a class C network. For the other
1369 networks in I<CSNETS>, the local machine's netmask will be used
1374 The user B<lisa> may run any command on any host in the I<CUNETS> alias
1375 (the class B network C<128.138.0.0>).
1377 operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
1378 sudoedit /etc/printcap, /usr/oper/bin/
1380 The B<operator> user may run commands limited to simple maintenance.
1381 Here, those are commands related to backups, killing processes, the
1382 printing system, shutting down the system, and any commands in the
1383 directory F</usr/oper/bin/>.
1385 joe ALL = /usr/bin/su operator
1387 The user B<joe> may only L<su(1)> to operator.
1389 pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root
1391 %opers ALL = (: ADMINGRP) /usr/sbin/
1393 Users in the B<opers> group may run commands in F</usr/sbin/> as themselves
1394 with any group in the I<ADMINGRP> C<Runas_Alias> (the B<adm> and B<oper>
1397 The user B<pete> is allowed to change anyone's password except for
1398 root on the I<HPPA> machines. Note that this assumes L<passwd(1)>
1399 does not take multiple usernames on the command line.
1401 bob SPARC = (OP) ALL : SGI = (OP) ALL
1403 The user B<bob> may run anything on the I<SPARC> and I<SGI> machines
1404 as any user listed in the I<OP> C<Runas_Alias> (B<root> and B<operator>).
1408 The user B<jim> may run any command on machines in the I<biglab> netgroup.
1409 B<sudo> knows that "biglab" is a netgroup due to the '+' prefix.
1411 +secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
1413 Users in the B<secretaries> netgroup need to help manage the printers
1414 as well as add and remove users, so they are allowed to run those
1415 commands on all machines.
1417 fred ALL = (DB) NOPASSWD: ALL
1419 The user B<fred> can run commands as any user in the I<DB> C<Runas_Alias>
1420 (B<oracle> or B<sybase>) without giving a password.
1422 john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
1424 On the I<ALPHA> machines, user B<john> may su to anyone except root
1425 but he is not allowed to specify any options to the L<su(1)> command.
1427 jen ALL, !SERVERS = ALL
1429 The user B<jen> may run any command on any machine except for those
1430 in the I<SERVERS> C<Host_Alias> (master, mail, www and ns).
1432 jill SERVERS = /usr/bin/, !SU, !SHELLS
1434 For any machine in the I<SERVERS> C<Host_Alias>, B<jill> may run
1435 any commands in the directory F</usr/bin/> except for those commands
1436 belonging to the I<SU> and I<SHELLS> C<Cmnd_Aliases>.
1438 steve CSNETS = (operator) /usr/local/op_commands/
1440 The user B<steve> may run any command in the directory /usr/local/op_commands/
1441 but only as user operator.
1443 matt valkyrie = KILL
1445 On his personal workstation, valkyrie, B<matt> needs to be able to
1446 kill hung processes.
1448 WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
1450 On the host www, any user in the I<WEBMASTERS> C<User_Alias> (will,
1451 wendy, and wim), may run any command as user www (which owns the
1452 web pages) or simply L<su(1)> to www.
1454 ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
1455 /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
1457 Any user may mount or unmount a CD-ROM on the machines in the CDROM
1458 C<Host_Alias> (orion, perseus, hercules) without entering a password.
1459 This is a bit tedious for users to type, so it is a prime candidate
1460 for encapsulating in a shell script.
1462 =head1 SECURITY NOTES
1464 It is generally not effective to "subtract" commands from C<ALL>
1465 using the '!' operator. A user can trivially circumvent this
1466 by copying the desired command to a different name and then
1467 executing that. For example:
1469 bill ALL = ALL, !SU, !SHELLS
1471 Doesn't really prevent B<bill> from running the commands listed in
1472 I<SU> or I<SHELLS> since he can simply copy those commands to a
1473 different name, or use a shell escape from an editor or other
1474 program. Therefore, these kind of restrictions should be considered
1475 advisory at best (and reinforced by policy).
1477 Furthermore, if the I<fast_glob> option is in use, it is not possible
1478 to reliably negate commands where the path name includes globbing
1479 (aka wildcard) characters. This is because the C library's
1480 L<fnmatch(3)> function cannot resolve relative paths. While this
1481 is typically only an inconvenience for rules that grant privileges,
1482 it can result in a security issue for rules that subtract or revoke
1485 For example, given the following I<sudoers> entry:
1487 john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,
1488 /usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
1490 User B<john> can still run C</usr/bin/passwd root> if I<fast_glob> is
1491 enabled by changing to F</usr/bin> and running C<./passwd root> instead.
1493 =head1 PREVENTING SHELL ESCAPES
1495 Once B<sudo> executes a program, that program is free to do whatever
1496 it pleases, including run other programs. This can be a security
1497 issue since it is not uncommon for a program to allow shell escapes,
1498 which lets a user bypass B<sudo>'s access control and logging.
1499 Common programs that permit shell escapes include shells (obviously),
1500 editors, paginators, mail and terminal programs.
1502 There are two basic approaches to this problem:
1508 Avoid giving users access to commands that allow the user to run
1509 arbitrary commands. Many editors have a restricted mode where shell
1510 escapes are disabled, though B<sudoedit> is a better solution to
1511 running editors via B<sudo>. Due to the large number of programs that
1512 offer shell escapes, restricting users to the set of programs that
1513 do not if often unworkable.
1517 Many systems that support shared libraries have the ability to
1518 override default library functions by pointing an environment
1519 variable (usually C<LD_PRELOAD>) to an alternate shared library.
1520 On such systems, B<sudo>'s I<noexec> functionality can be used to
1521 prevent a program run by B<sudo> from executing any other programs.
1522 Note, however, that this applies only to native dynamically-linked
1523 executables. Statically-linked executables and foreign executables
1524 running under binary emulation are not affected.
1526 To tell whether or not B<sudo> supports I<noexec>, you can run
1527 the following as root:
1529 sudo -V | grep "dummy exec"
1531 If the resulting output contains a line that begins with:
1533 File containing dummy exec functions:
1535 then B<sudo> may be able to replace the exec family of functions
1536 in the standard library with its own that simply return an error.
1537 Unfortunately, there is no foolproof way to know whether or not
1538 I<noexec> will work at compile-time. I<noexec> should work on
1539 SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX
1540 11.x. It is known B<not> to work on AIX and UnixWare. I<noexec>
1541 is expected to work on most operating systems that support the
1542 C<LD_PRELOAD> environment variable. Check your operating system's
1543 manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld,
1544 dld.sl, rld, or loader) to see if C<LD_PRELOAD> is supported.
1546 To enable I<noexec> for a command, use the C<NOEXEC> tag as documented
1547 in the User Specification section above. Here is that example again:
1549 aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
1551 This allows user B<aaron> to run F</usr/bin/more> and F</usr/bin/vi>
1552 with I<noexec> enabled. This will prevent those two commands from
1553 executing other commands (such as a shell). If you are unsure
1554 whether or not your system is capable of supporting I<noexec> you
1555 can always just try it out and see if it works.
1559 Note that restricting shell escapes is not a panacea. Programs
1560 running as root are still capable of many potentially hazardous
1561 operations (such as changing or overwriting files) that could lead
1562 to unintended privilege escalation. In the specific case of an
1563 editor, a safer approach is to give the user permission to run
1568 L<rsh(1)>, L<su(1)>, L<fnmatch(3)>, L<glob(3)>, L<sudo(8)>, L<visudo(8)>
1572 The I<sudoers> file should B<always> be edited by the B<visudo>
1573 command which locks the file and does grammatical checking. It is
1574 imperative that I<sudoers> be free of syntax errors since B<sudo>
1575 will not run with a syntactically incorrect I<sudoers> file.
1577 When using netgroups of machines (as opposed to users), if you
1578 store fully qualified hostnames in the netgroup (as is usually the
1579 case), you either need to have the machine's hostname be fully qualified
1580 as returned by the C<hostname> command or use the I<fqdn> option in
1585 If you feel you have found a bug in B<sudo>, please submit a bug report
1586 at http://www.sudo.ws/sudo/bugs/
1590 Limited free support is available via the sudo-users mailing list,
1591 see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
1592 search the archives.
1596 B<sudo> is provided ``AS IS'' and any express or implied warranties,
1597 including, but not limited to, the implied warranties of merchantability
1598 and fitness for a particular purpose are disclaimed. See the LICENSE
1599 file distributed with B<sudo> or http://www.sudo.ws/sudo/license.html
1600 for complete details.