path: root/sudoers.pod

=cut
Copyright (c) 1994-1996,1998-2004 Todd C. Miller <Todd.Miller@courtesan.com>
All rights reserved.

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Sponsored in part by the Defense Advanced Research Projects
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Materiel Command, USAF, under agreement number F39502-99-1-0512.

$Sudo$
=pod

=head1 NAME

sudoers - list of which users may execute what

=head1 DESCRIPTION

The I<sudoers> file is composed of two types of entries:
aliases (basically variables) and user specifications
(which specify who may run what).  The grammar of I<sudoers>
will be described below in Extended Backus-Naur Form (EBNF).
Don't despair if you don't know what EBNF is; it is fairly
simple, and the definitions below are annotated.

=head2 Quick guide to EBNF

EBNF is a concise and exact way of describing the grammar of a language.
Each EBNF definition is made up of I<production rules>.  E.g.,

 symbol ::= definition | alternate1 | alternate2 ...

Each I<production rule> references others and thus makes up a
grammar for the language.  EBNF also contains the following
operators, which many readers will recognize from regular
expressions.  Do not, however, confuse them with "wildcard"
characters, which have different meanings.

=over 8

=item C<?>

Means that the preceding symbol (or group of symbols) is optional.
That is, it may appear once or not at all.

=item C<*>

Means that the preceding symbol (or group of symbols) may appear
zero or more times.

=item C<+>

Means that the preceding symbol (or group of symbols) may appear
one or more times.

=back

Parentheses may be used to group symbols together.  For clarity,
we will use single quotes ('') to designate what is a verbatim character
string (as opposed to a symbol name).

=head2 Aliases

There are four kinds of aliases: C<User_Alias>, C<Runas_Alias>,
C<Host_Alias> and C<Cmnd_Alias>.

 Alias ::= 'User_Alias'  User_Alias (':' User_Alias)* |
	   'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
	   'Host_Alias'  Host_Alias (':' Host_Alias)* |
	   'Cmnd_Alias'  Cmnd_Alias (':' Cmnd_Alias)*

 User_Alias ::= NAME '=' User_List

 Runas_Alias ::= NAME '=' Runas_List

 Host_Alias ::= NAME '=' Host_List

 Cmnd_Alias ::= NAME '=' Cmnd_List

 NAME ::= [A-Z]([A-Z][0-9]_)*

Each I<alias> definition is of the form

 Alias_Type NAME = item1, item2, ...

where I<Alias_Type> is one of C<User_Alias>, C<Runas_Alias>, C<Host_Alias>,
or C<Cmnd_Alias>.  A C<NAME> is a string of uppercase letters, numbers,
and underscore characters ('_').  A C<NAME> B<must> start with an
uppercase letter.  It is possible to put several alias definitions
of the same type on a single line, joined by a colon (':').  E.g.,

 Alias_Type NAME = item1, item2, item3 : NAME = item4, item5

The definitions of what constitutes a valid I<alias> member follow.

 User_List ::= User |
	       User ',' User_List

 User ::= '!'* username |
	  '!'* '%'group |
	  '!'* '+'netgroup |
	  '!'* User_Alias

A C<User_List> is made up of one or more usernames, uids
(prefixed with '#'), System groups (prefixed with '%'),
netgroups (prefixed with '+') and other aliases.  Each list
item may be prefixed with one or more '!' operators.  An odd number
of '!' operators negate the value of the item; an even number
just cancel each other out.

 Runas_List ::= Runas_User |
		Runas_User ',' Runas_List

 Runas_User ::= '!'* username |
	        '!'* '#'uid |
	        '!'* '%'group |
	        '!'* +netgroup |
	        '!'* Runas_Alias

A C<Runas_List> is similar to a C<User_List> except that it can
also contain uids (prefixed with '#') and instead of C<User_Alias>es
it can contain C<Runas_Alias>es.

 Host_List ::= Host |
	       Host ',' Host_List

 Host ::= '!'* hostname |
	  '!'* ip_addr |
	  '!'* network(/netmask)? |
	  '!'* '+'netgroup |
	  '!'* Host_Alias

A C<Host_List> is made up of one or more hostnames, IP addresses,
network numbers, netgroups (prefixed with '+') and other aliases.
Again, the value of an item may be negated with the '!' operator.
If you do not specify a netmask with a network number, the netmask
of the host's ethernet interface(s) will be used when matching.
The netmask may be specified either in dotted quad notation (e.g.
255.255.255.0) or CIDR notation (number of bits, e.g. 24).  A hostname
may include shell-style wildcards (see `Wildcards' section below),
but unless the C<hostname> command on your machine returns the fully
qualified hostname, you'll need to use the I<fqdn> option for wildcards
to be useful.

 Cmnd_List ::= Cmnd |
	       Cmnd ',' Cmnd_List

 commandname ::= filename |
	         filename args |
	         filename '""'

 Cmnd ::= '!'* commandname |
	  '!'* directory |
	  '!'* "sudoedit" |
	  '!'* Cmnd_Alias

A C<Cmnd_List> is a list of one or more commandnames, directories, and other
aliases.  A commandname is a fully qualified filename which may include
shell-style wildcards (see `Wildcards' section below).  A simple
filename allows the user to run the command with any arguments he/she
wishes.  However, you may also specify command line arguments (including
wildcards).  Alternately, you can specify C<""> to indicate that the command
may only be run B<without> command line arguments.  A directory is a
fully qualified pathname ending in a '/'.  When you specify a directory
in a C<Cmnd_List>, the user will be able to run any file within that directory
(but not in any subdirectories therein).

If a C<Cmnd> has associated command line arguments, then the arguments
in the C<Cmnd> must match exactly those given by the user on the command line
(or match the wildcards if there are any).  Note that the following
characters must be escaped with a '\' if they are used in command
arguments: ',', ':', '=', '\'.  The special command C<"sudoedit">
is used to permit a user to run B<sudo> with the B<-e> flag (or
as B<sudoedit>).  It may take command line arguments just as
a normal command does.

=head2 Defaults

Certain configuration options may be changed from their default
values at runtime via one or more C<Default_Entry> lines.  These
may affect all users on any host, all users on a specific host, a
specific user, or commands being run as a specific user.  When
multiple entries match, they are applied in order.  Where there are
conflicting values, the last value on a matching line takes effect.

 Default_Type ::= 'Defaults' |
		  'Defaults' '@' Host |
		  'Defaults' ':' User |
		  'Defaults' '>' RunasUser

 Default_Entry ::= Default_Type Parameter_List

 Parameter_List ::= Parameter |
		    Parameter ',' Parameter_List

 Parameter ::= Parameter '=' Value |
	       Parameter '+=' Value |
	       Parameter '-=' Value |
	       '!'* Parameter

Parameters may be B<flags>, B<integer> values, B<strings>, or B<lists>.
Flags are implicitly boolean and can be turned off via the '!'
operator.  Some integer, string and list parameters may also be
used in a boolean context to disable them.  Values may be enclosed
in double quotes (C<">) when they contain multiple words.  Special
characters may be escaped with a backslash (C<\>).

Lists have two additional assignment operators, C<+=> and C<-=>.
These operators are used to add to and delete from a list respectively.
It is not an error to use the C<-=> operator to remove an element
that does not exist in a list.

Note that since the I<sudoers> file is parsed in order the best place
to put the Defaults section is after the Host, User, and Cmnd aliases
but before the user specifications.

B<Flags>:

=over 12

=item long_otp_prompt

When validating with a One Time Password scheme (B<S/Key> or B<OPIE>),
a two-line prompt is used to make it easier to cut and paste the
challenge to a local window.  It's not as pretty as the default but
some people find it more convenient.  This flag is I<@long_otp_prompt@>
by default.

=item ignore_dot

If set, B<sudo> will ignore '.' or '' (current dir) in the C<PATH>
environment variable; the C<PATH> itself is not modified.  This
flag is I<@ignore_dot@> by default.  Currently, while it is possible
to set I<ignore_dot> in I<sudoers>, its value is not used.  This option
should be considered read-only (it will be fixed in a future version
of B<sudo>).

=item mail_always

Send mail to the I<mailto> user every time a users runs B<sudo>.
This flag is I<off> by default.

=item mail_badpass

Send mail to the I<mailto> user if the user running sudo does not
enter the correct password.  This flag is I<off> by default.

=item mail_no_user

If set, mail will be sent to the I<mailto> user if the invoking
user is not in the I<sudoers> file.  This flag is I<@mail_no_user@>
by default.

=item mail_no_host

If set, mail will be sent to the I<mailto> user if the invoking
user exists in the I<sudoers> file, but is not allowed to run
commands on the current host.  This flag is I<@mail_no_host@> by default.

=item mail_no_perms

If set, mail will be sent to the I<mailto> user if the invoking
user is allowed to use B<sudo> but the command they are trying is not
listed in their I<sudoers> file entry.  This flag is I<@mail_no_perms@>
by default.

=item tty_tickets

If set, users must authenticate on a per-tty basis.  Normally,
B<sudo> uses a directory in the ticket dir with the same name as
the user running it.  With this flag enabled, B<sudo> will use a
file named for the tty the user is logged in on in that directory.
This flag is I<@tty_tickets@> by default.

=item authenticate

If set, users must authenticate themselves via a password (or other
means of authentication) before they may run commands.  This default
may be overridden via the C<PASSWD> and C<NOPASSWD> tags.
This flag is I<on> by default.

=item root_sudo

If set, root is allowed to run B<sudo> too.  Disabling this prevents users
from "chaining" B<sudo> commands to get a root shell by doing something
like C<"sudo sudo /bin/sh">.  Note, however, that turning off I<root_sudo>
will also prevent root and from running B<sudoedit>.
Disabling I<root_sudo> provides no real additional security; it
exists purely for historical reasons.
This flag is I<@root_sudo@> by default.

=item log_host

If set, the hostname will be logged in the (non-syslog) B<sudo> log file.
This flag is I<off> by default.

=item log_year

If set, the four-digit year will be logged in the (non-syslog) B<sudo> log file.
This flag is I<off> by default.

=item shell_noargs

If set and B<sudo> is invoked with no arguments it acts as if the
B<-s> flag had been given.  That is, it runs a shell as root (the
shell is determined by the C<SHELL> environment variable if it is
set, falling back on the shell listed in the invoking user's
/etc/passwd entry if not).  This flag is I<off> by default.

=item set_home

If set and B<sudo> is invoked with the B<-s> flag the C<HOME>
environment variable will be set to the home directory of the target
user (which is root unless the B<-u> option is used).  This effectively
makes the B<-s> flag imply B<-H>.  This flag is I<off> by default.

=item always_set_home

If set, B<sudo> will set the C<HOME> environment variable to the home
directory of the target user (which is root unless the B<-u> option is used).
This effectively means that the B<-H> flag is always implied.
This flag is I<off> by default.

=item path_info

Normally, B<sudo> will tell the user when a command could not be
found in their C<PATH> environment variable.  Some sites may wish
to disable this as it could be used to gather information on the
location of executables that the normal user does not have access
to.  The disadvantage is that if the executable is simply not in
the user's C<PATH>, B<sudo> will tell the user that they are not
allowed to run it, which can be confusing.  This flag is I<off> by
default.

=item preserve_groups

By default B<sudo> will initialize the group vector to the list of
groups the target user is in.  When I<preserve_groups> is set, the
user's existing group vector is left unaltered.  The real and
effective group IDs, however, are still set to match the target
user.  This flag is I<off> by default.

=item fqdn

Set this flag if you want to put fully qualified hostnames in the
I<sudoers> file.  I.e., instead of myhost you would use myhost.mydomain.edu.
You may still use the short form if you wish (and even mix the two).
Beware that turning on I<fqdn> requires B<sudo> to make DNS lookups
which may make B<sudo> unusable if DNS stops working (for example
if the machine is not plugged into the network).  Also note that
you must use the host's official name as DNS knows it.  That is,
you may not use a host alias (C<CNAME> entry) due to performance
issues and the fact that there is no way to get all aliases from
DNS.  If your machine's hostname (as returned by the C<hostname>
command) is already fully qualified you shouldn't need to set
I<fqdn>.  This flag is I<@fqdn@> by default.

=item insults

If set, B<sudo> will insult users when they enter an incorrect
password.  This flag is I<@insults@> by default.

=item requiretty

If set, B<sudo> will only run when the user is logged in to a real
tty.  This will disallow things like C<"rsh somehost sudo ls"> since
rsh(1) does not allocate a tty.  Because it is not possible to turn
off echo when there is no tty present, some sites may with to set
this flag to prevent a user from entering a visible password.  This
flag is I<off> by default.

=item env_editor

If set, B<visudo> will use the value of the EDITOR or VISUAL
environment variables before falling back on the default editor list.
Note that this may create a security hole as it allows the user to
run any arbitrary command as root without logging.  A safer alternative
is to place a colon-separated list of editors in the C<editor>
variable.  B<visudo> will then only use the EDITOR or VISUAL if
they match a value specified in C<editor>.  This flag is C<@env_editor@> by
default.

=item rootpw

If set, B<sudo> will prompt for the root password instead of the password
of the invoking user.  This flag is I<off> by default.

=item runaspw

If set, B<sudo> will prompt for the password of the user defined by the
I<runas_default> option (defaults to C<@runas_default@>) instead of the
password of the invoking user.  This flag is I<off> by default.

=item targetpw

If set, B<sudo> will prompt for the password of the user specified by
the B<-u> flag (defaults to C<root>) instead of the password of the
invoking user.  This flag is I<off> by default.

=item set_logname

Normally, B<sudo> will set the C<LOGNAME> and C<USER> environment variables
to the name of the target user (usually root unless the B<-u> flag is given).
However, since some programs (including the RCS revision control system)
use C<LOGNAME> to determine the real identity of the user, it may be desirable
to change this behavior.  This can be done by negating the set_logname option.

=item stay_setuid

Normally, when B<sudo> executes a command the real and effective
UIDs are set to the target user (root by default).  This option
changes that behavior such that the real UID is left as the invoking
user's UID.  In other words, this makes B<sudo> act as a setuid
wrapper.  This can be useful on systems that disable some potentially
dangerous functionality when a program is run setuid.  Note, however,
that this means that sudo will run with the real uid of the invoking
user which may allow that user to kill B<sudo> before it can log a
failure, depending on how your OS defines the interaction between
signals and setuid processes.

=item env_reset

If set, B<sudo> will reset the environment to only contain the
following variables: C<HOME>, C<LOGNAME>, C<PATH>, C<SHELL>, C<TERM>,
and C<USER> (in addition to the C<SUDO_*> variables).
Of these, only C<TERM> is copied unaltered from the old environment.
The other variables are set to default values (possibly modified
by the value of the I<set_logname> option).  If B<sudo> was compiled
with the C<SECURE_PATH> option, its value will be used for the C<PATH>
environment variable.
Other variables may be preserved with the I<env_keep> option.

=item use_loginclass

If set, B<sudo> will apply the defaults specified for the target user's
login class if one exists.  Only available if B<sudo> is configured with
the --with-logincap option.  This flag is I<off> by default.

=item noexec

If set, all commands run via sudo will behave as if the C<NOEXEC>
tag has been set, unless overridden by a C<EXEC> tag.  See the
description of I<NOEXEC and EXEC> below as well as the B<PREVENTING SHELL
ESCAPES> section at the end of this manual.  This flag is I<off> by default.

=back

B<Integers>:

=over 12

=item passwd_tries

The number of tries a user gets to enter his/her password before
B<sudo> logs the failure and exits.  The default is C<@passwd_tries@>.

=back

B<Integers that can be used in a boolean context>:

=over 12

=item loglinelen

Number of characters per line for the file log.  This value is used
to decide when to wrap lines for nicer log files.  This has no
effect on the syslog log file, only the file log.  The default is
C<@loglen@> (use 0 or negate the option to disable word wrap).

=item timestamp_timeout

Number of minutes that can elapse before B<sudo> will ask for a
passwd again.  The default is C<@timeout@>.  Set this to C<0> to always
prompt for a password.
If set to a value less than C<0> the user's timestamp will never
expire.  This can be used to allow users to create or delete their
own timestamps via C<sudo -v> and C<sudo -k> respectively.

=item passwd_timeout

Number of minutes before the B<sudo> password prompt times out.
The default is C<@password_timeout@>, set this to C<0> for no password timeout.

=item umask

Umask to use when running the command.  Negate this option or set
it to 0777 to preserve the user's umask.  The default is C<@sudo_umask@>.

=back

B<Strings>:

=over 12

=item mailsub

Subject of the mail sent to the I<mailto> user. The escape C<%h>
will expand to the hostname of the machine.
Default is C<@mailsub@>.

=item badpass_message

Message that is displayed if a user enters an incorrect password.
The default is C<@badpass_message@> unless insults are enabled.

=item timestampdir

The directory in which B<sudo> stores its timestamp files.
The default is F<@timedir@>.

=item timestampowner

The owner of the timestamp directory and the timestamps stored therein.
The default is C<root>.

=item passprompt

The default prompt to use when asking for a password; can be overridden
via the B<-p> option or the C<SUDO_PROMPT> environment variable.
The following percent (`C<%>') escapes are supported:

=over 8

=item C<%u>

expanded to the invoking user's login name

=item C<%U>

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

=item C<%h>

expanded to the local hostname without the domain name

=item C<%H>

expanded to the local hostname including the domain name
(on if the machine's hostname is fully qualified or the I<fqdn>
option is set)

=item C<%%>

two consecutive C<%> characters are collaped into a single C<%> character

=back 8

The default value is C<@passprompt@>.

=item runas_default

The default user to run commands as if the B<-u> flag is not specified
on the command line.  This defaults to C<@runas_default@>.

=item syslog_goodpri

Syslog priority to use when user authenticates successfully.
Defaults to C<@goodpri@>.

=item syslog_badpri

Syslog priority to use when user authenticates unsuccessfully.
Defaults to C<@badpri@>.

=item editor

A colon (':') separated list of editors allowed to be used with
B<visudo>.  B<visudo> will choose the editor that matches the user's
USER environment variable if possible, or the first editor in the
list that exists and is executable.  The default is the path to vi
on your system.

=item noexec_file

Path to a shared library containing dummy versions of the execv(),
execve() and fexecve() library functions that just return an error.
This is used to implement the I<noexec> functionality on systems that
support C<LD_PRELOAD> or its equivalent.  Defaults to F<@noexec_file@>.

=back

B<Strings that can be used in a boolean context>:

=over 12

=item lecture

This option controls when a short lecture will be printed along with
the password prompt.  It has the following possible values:

=over 8

=item never

Never lecture the user.

=item once

Only lecture the user the first time they run B<sudo>.

=item always

Always lecture the user.

=back

The default value is I<@lecture@>.

=item lecture_file

Path to a file containing an alternate sudo lecture that will
be used in place of the standard lecture if the named file exists.

=item logfile

Path to the B<sudo> log file (not the syslog log file).  Setting a path
turns on logging to a file; negating this option turns it off.

=item syslog

Syslog facility if syslog is being used for logging (negate to
disable syslog logging).  Defaults to C<@logfac@>.

=item mailerpath

Path to mail program used to send warning mail.
Defaults to the path to sendmail found at configure time.

=item mailerflags

Flags to use when invoking mailer. Defaults to B<-t>.

=item mailto

Address to send warning and error mail to.  The address should
be enclosed in double quotes (C<">) to protect against sudo
interpreting the C<@> sign.  Defaults to C<@mailto@>.

=item exempt_group

Users in this group are exempt from password and PATH requirements.
This is not set by default.

=item verifypw

This option controls when a password will be required when a user runs
B<sudo> with the B<-v> flag.  It has the following possible values:

=over 8

=item all

All the user's I<sudoers> entries for the current host must have
the C<NOPASSWD> flag set to avoid entering a password.

=item any

At least one of the user's I<sudoers> entries for the current host
must have the C<NOPASSWD> flag set to avoid entering a password.

=item never

The user need never enter a password to use the B<-v> flag.

=item always

The user must always enter a password to use the B<-v> flag.

=back

The default value is `all'.

=item listpw

This option controls when a password will be required when a
user runs B<sudo> with the B<-l> flag.  It has the following possible values:

=over 8

=item all

All the user's I<sudoers> entries for the current host must have
the C<NOPASSWD> flag set to avoid entering a password.

=item any

At least one of the user's I<sudoers> entries for the current host
must have the C<NOPASSWD> flag set to avoid entering a password.

=item never

The user need never enter a password to use the B<-l> flag.

=item always

The user must always enter a password to use the B<-l> flag.

=back

The default value is `any'.

=back

B<Lists that can be used in a boolean context>:

=over 12

=item env_check

Environment variables to be removed from the user's environment if
the variable's value contains C<%> or C</> characters.  This can
be used to guard against printf-style format vulnerabilities in
poorly-written programs.  The argument may be a double-quoted,
space-separated list or a single value without double-quotes.  The
list can be replaced, added to, deleted from, or disabled by using
the C<=>, C<+=>, C<-=>, and C<!> operators respectively.  The default
list of environment variables to check is printed when B<sudo> is
run by root with the I<-V> option.

=item env_delete

Environment variables to be removed from the user's environment.
The argument may be a double-quoted, space-separated list or a
single value without double-quotes.  The list can be replaced, added
to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and
C<!> operators respectively.  The default list of environment
variables to remove is printed when B<sudo> is run by root with the
I<-V> option.  Note that many operating systems will remove potentially
dangerous variables from the environment of any setuid process (such
as B<sudo>).

=item env_keep

Environment variables to be preserved in the user's environment
when the I<env_reset> option is in effect.  This allows fine-grained
control over the environment B<sudo>-spawned processes will receive.
The argument may be a double-quoted, space-separated list or a
single value without double-quotes.  The list can be replaced, added
to, deleted from, or disabled by using the C<=>, C<+=>, C<-=>, and
C<!> operators respectively.  This list has no default members.

=back

When logging via syslog(3), B<sudo> accepts the following values for the syslog
facility (the value of the B<syslog> Parameter): B<authpriv> (if your OS
supports it), B<auth>, B<daemon>, B<user>, B<local0>, B<local1>, B<local2>,
B<local3>, B<local4>, B<local5>, B<local6>, and B<local7>.  The following
syslog priorities are supported: B<alert>, B<crit>, B<debug>, B<emerg>,
B<err>, B<info>, B<notice>, and B<warning>.

=head2 User Specification

 User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
	       (':' Host_List '=' Cmnd_Spec_List)*

 Cmnd_Spec_List ::= Cmnd_Spec |
		    Cmnd_Spec ',' Cmnd_Spec_List

 Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd

 Runas_Spec ::= '(' Runas_List ')'

 Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:')

A B<user specification> determines which commands a user may run
(and as what user) on specified hosts.  By default, commands are
run as B<root>, but this can be changed on a per-command basis.

Let's break that down into its constituent parts:

=head2 Runas_Spec

A C<Runas_Spec> is simply a C<Runas_List> (as defined above)
enclosed in a set of parentheses.  If you do not specify a
C<Runas_Spec> in the user specification, a default C<Runas_Spec>
of B<root> will be used.  A C<Runas_Spec> sets the default for
commands that follow it.  What this means is that for the entry:

 dgb	boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm

The user B<dgb> may run F</bin/ls>, F</bin/kill>, and
F</usr/bin/lprm> -- but only as B<operator>.  E.g.,

    sudo -u operator /bin/ls.

It is also possible to override a C<Runas_Spec> later on in an
entry.  If we modify the entry like so:

 dgb	boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm

Then user B<dgb> is now allowed to run F</bin/ls> as B<operator>,
but  F</bin/kill> and F</usr/bin/lprm> as B<root>.

=head2 Tag_Spec

A command may have zero or more tags associated with it.  There are
four possible tag values, C<NOPASSWD>, C<PASSWD>, C<NOEXEC>, C<EXEC>.
Once a tag is set on a C<Cmnd>, subsequent C<Cmnd>s in the
C<Cmnd_Spec_List>, inherit the tag unless it is overridden by the
opposite tag (ie: C<PASSWD> overrides C<NOPASSWD> and C<EXEC>
overrides C<NOEXEC>).

=head3 NOPASSWD and PASSWD

By default, B<sudo> requires that a user authenticate him or herself
before running a command.  This behavior can be modified via the
C<NOPASSWD> tag.  Like a C<Runas_Spec>, the C<NOPASSWD> tag sets
a default for the commands that follow it in the C<Cmnd_Spec_List>.
Conversely, the C<PASSWD> tag can be used to reverse things.
For example:

 ray	rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm

would allow the user B<ray> to run F</bin/kill>, F</bin/ls>, and
F</usr/bin/lprm> as root on the machine rushmore as B<root> without
authenticating himself.  If we only want B<ray> to be able to
run F</bin/kill> without a password the entry would be:

 ray	rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm

Note, however, that the C<PASSWD> tag has no effect on users who are
in the group specified by the exempt_group option.

By default, if the C<NOPASSWD> tag is applied to any of the entries
for a user on the current host, he or she will be able to run
C<sudo -l> without a password.  Additionally, a user may only run
C<sudo -v> without a password if the C<NOPASSWD> tag is present
for all a user's entries that pertain to the current host.
This behavior may be overridden via the verifypw and listpw options.

=head3 NOEXEC and EXEC

If sudo has been compiled with I<noexec> support and the underlying
operating system support it, the C<NOEXEC> tag can be used to prevent
a dynamically-linked executable from running further commands itself.

In the following example, user B<aaron> may run F</usr/bin/more>
and F</usr/bin/vi> but shell escapes will be disabled.

 aaron	shanty = NOEXEC: /usr/bin/more, /usr/bin/vi

See the B<PREVENTING SHELL ESCAPES> section below for more details
on how I<noexec> works and whether or not it will work on your system.

=head2 Wildcards (aka meta characters):

B<sudo> allows shell-style I<wildcards> to be used in pathnames
as well as command line arguments in the I<sudoers> file.  Wildcard
matching is done via the B<POSIX> C<fnmatch(3)> routine.  Note that
these are I<not> regular expressions.

=over 8

=item C<*>

Matches any set of zero or more characters.

=item C<?>

Matches any single character.

=item C<[...]>

Matches any character in the specified range.

=item C<[!...]>

Matches any character B<not> in the specified range.

=item C<\x>

For any character "x", evaluates to "x".  This is used to
escape special characters such as: "*", "?", "[", and "}".

=back

Note that a forward slash ('/') will B<not> be matched by
wildcards used in the pathname.  When matching the command
line arguments, however, a slash B<does> get matched by
wildcards.  This is to make a path like:

    /usr/bin/*

match F</usr/bin/who> but not F</usr/bin/X11/xterm>.

=head2 Exceptions to wildcard rules:

The following exceptions apply to the above rules:

=over 8

=item C<"">

If the empty string C<""> is the only command line argument in the
I<sudoers> entry it means that command is not allowed to be run
with B<any> arguments.

=back

=head2 Other special characters and reserved words:

The pound sign ('#') is used to indicate a comment (unless it
occurs in the context of a user name and is followed by one or
more digits, in which case it is treated as a uid).  Both the
comment character and any text after it, up to the end of the line,
are ignored.

The reserved word B<ALL> is a built-in I<alias> that always causes
a match to succeed.  It can be used wherever one might otherwise
use a C<Cmnd_Alias>, C<User_Alias>, C<Runas_Alias>, or C<Host_Alias>.
You should not try to define your own I<alias> called B<ALL> as the
built-in alias will be used in preference to your own.  Please note
that using B<ALL> can be dangerous since in a command context, it
allows the user to run B<any> command on the system.

An exclamation point ('!') can be used as a logical I<not> operator
both in an I<alias> and in front of a C<Cmnd>.  This allows one to
exclude certain values.  Note, however, that using a C<!> in
conjunction with the built-in C<ALL> alias to allow a user to
run "all but a few" commands rarely works as intended (see SECURITY
NOTES below).

Long lines can be continued with a backslash ('\') as the last
character on the line.

Whitespace between elements in a list as well as special syntactic
characters in a I<User Specification> ('=', ':', '(', ')') is optional.

The following characters must be escaped with a backslash ('\') when
used as part of a word (e.g. a username or hostname):
'@', '!', '=', ':', ',', '(', ')', '\'.

=head1 EXAMPLES

Below are example I<sudoers> entries.  Admittedly, some of
these are a bit contrived.  First, we define our I<aliases>:

 # User alias specification
 User_Alias	FULLTIMERS = millert, mikef, dowdy
 User_Alias	PARTTIMERS = bostley, jwfox, crawl
 User_Alias	WEBMASTERS = will, wendy, wim

 # Runas alias specification
 Runas_Alias	OP = root, operator
 Runas_Alias	DB = oracle, sybase

 # Host alias specification
 Host_Alias	SPARC = bigtime, eclipse, moet, anchor :\
		SGI = grolsch, dandelion, black :\
		ALPHA = widget, thalamus, foobar :\
		HPPA = boa, nag, python
 Host_Alias	CUNETS = 128.138.0.0/255.255.0.0
 Host_Alias	CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
 Host_Alias	SERVERS = master, mail, www, ns
 Host_Alias	CDROM = orion, perseus, hercules

 # Cmnd alias specification
 Cmnd_Alias	DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
			/usr/sbin/restore, /usr/sbin/rrestore
 Cmnd_Alias	KILL = /usr/bin/kill
 Cmnd_Alias	PRINTING = /usr/sbin/lpc, /usr/bin/lprm
 Cmnd_Alias	SHUTDOWN = /usr/sbin/shutdown
 Cmnd_Alias	HALT = /usr/sbin/halt, /usr/sbin/fasthalt
 Cmnd_Alias	REBOOT = /usr/sbin/reboot, /usr/sbin/fastboot
 Cmnd_Alias	SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
			 /usr/local/bin/tcsh, /usr/bin/rsh, \
			 /usr/local/bin/zsh
 Cmnd_Alias	SU = /usr/bin/su

Here we override some of the compiled in default values.  We want
B<sudo> to log via syslog(3) using the I<auth> facility in all
cases.  We don't want to subject the full time staff to the B<sudo>
lecture, user B<millert> need not give a password, and we don't
want to set the C<LOGNAME> or C<USER> environment variables when
running commands as root.  Additionally, on the machines in the
I<SERVERS> C<Host_Alias>, we keep an additional local log file and
make sure we log the year in each log line since the log entries
will be kept around for several years.

 # Override built-in defaults
 Defaults		syslog=auth
 Defaults>root		!set_logname
 Defaults:FULLTIMERS	!lecture
 Defaults:millert	!authenticate
 Defaults@SERVERS	log_year, logfile=/var/log/sudo.log

The I<User specification> is the part that actually determines who may
run what.

 root		ALL = (ALL) ALL
 %wheel		ALL = (ALL) ALL

We let B<root> and any user in group B<wheel> run any command on any
host as any user.

 FULLTIMERS	ALL = NOPASSWD: ALL

Full time sysadmins (B<millert>, B<mikef>, and B<dowdy>) may run any
command on any host without authenticating themselves.

 PARTTIMERS	ALL = ALL

Part time sysadmins (B<bostley>, B<jwfox>, and B<crawl>) may run any
command on any host but they must authenticate themselves first
(since the entry lacks the C<NOPASSWD> tag).

 jack		CSNETS = ALL

The user B<jack> may run any command on the machines in the I<CSNETS> alias
(the networks C<128.138.243.0>, C<128.138.204.0>, and C<128.138.242.0>).
Of those networks, only C<128.138.204.0> has an explicit netmask (in
CIDR notation) indicating it is a class C network.  For the other
networks in I<CSNETS>, the local machine's netmask will be used
during matching.

 lisa		CUNETS = ALL

The user B<lisa> may run any command on any host in the I<CUNETS> alias
(the class B network C<128.138.0.0>).

 operator	ALL = DUMPS, KILL, PRINTING, SHUTDOWN, HALT, REBOOT,\
		/usr/oper/bin/

The B<operator> user may run commands limited to simple maintenance.
Here, those are commands related to backups, killing processes, the
printing system, shutting down the system, and any commands in the
directory F</usr/oper/bin/>.

 joe		ALL = /usr/bin/su operator

The user B<joe> may only su(1) to operator.

 pete		HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root

The user B<pete> is allowed to change anyone's password except for
root on the I<HPPA> machines.  Note that this assumes passwd(1)
does not take multiple usernames on the command line.

 bob		SPARC = (OP) ALL : SGI = (OP) ALL

The user B<bob> may run anything on the I<SPARC> and I<SGI> machines
as any user listed in the I<OP> C<Runas_Alias> (B<root> and B<operator>).

 jim		+biglab = ALL

The user B<jim> may run any command on machines in the I<biglab> netgroup.
B<Sudo> knows that "biglab" is a netgroup due to the '+' prefix.

 +secretaries	ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser

Users in the B<secretaries> netgroup need to help manage the printers
as well as add and remove users, so they are allowed to run those
commands on all machines.

 fred		ALL = (DB) NOPASSWD: ALL

The user B<fred> can run commands as any user in the I<DB> C<Runas_Alias>
(B<oracle> or B<sybase>) without giving a password.

 john		ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*

On the I<ALPHA> machines, user B<john> may su to anyone except root
but he is not allowed to give su(1) any flags.

 jen		ALL, !SERVERS = ALL

The user B<jen> may run any command on any machine except for those
in the I<SERVERS> C<Host_Alias> (master, mail, www and ns).

 jill		SERVERS = /usr/bin/, !SU, !SHELLS

For any machine in the I<SERVERS> C<Host_Alias>, B<jill> may run
any commands in the directory /usr/bin/ except for those commands
belonging to the I<SU> and I<SHELLS> C<Cmnd_Aliases>.

 steve		CSNETS = (operator) /usr/local/op_commands/

The user B<steve> may run any command in the directory /usr/local/op_commands/
but only as user operator.

 matt		valkyrie = KILL

On his personal workstation, valkyrie, B<matt> needs to be able to
kill hung processes.

 WEBMASTERS	www = (www) ALL, (root) /usr/bin/su www

On the host www, any user in the I<WEBMASTERS> C<User_Alias> (will,
wendy, and wim), may run any command as user www (which owns the
web pages) or simply su(1) to www.

 ALL		CDROM = NOPASSWD: /sbin/umount /CDROM,\
		/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM

Any user may mount or unmount a CD-ROM on the machines in the CDROM
C<Host_Alias> (orion, perseus, hercules) without entering a password.
This is a bit tedious for users to type, so it is a prime candidate
for encapsulating in a shell script.

=head1 SECURITY NOTES

It is generally not effective to "subtract" commands from C<ALL>
using the '!' operator.  A user can trivially circumvent this
by copying the desired command to a different name and then
executing that.  For example:

    bill	ALL = ALL, !SU, !SHELLS

Doesn't really prevent B<bill> from running the commands listed in
I<SU> or I<SHELLS> since he can simply copy those commands to a
different name, or use a shell escape from an editor or other
program.  Therefore, these kind of restrictions should be considered
advisory at best (and reinforced by policy).

=head1 PREVENTING SHELL ESCAPES

Once B<sudo> executes a program, that program is free to do whatever
it pleases, including run other programs.  This can be a security
issue since it is not uncommon for a program to allow shell escapes,
which lets a user bypass B<sudo>'s restrictions.  Common programs
that permit shell escapes include shells (obviously), editors,
paginators, mail and terminal programs.

Many systems that support shared libraries have the ability to
override default library functions by pointing an environment
variable (usually C<LD_PRELOAD>) to an alternate shared library.
On such systems, B<sudo>'s I<noexec> functionality can be used to
prevent a program run by sudo from executing any other programs.
Note, however, that this applies only to native dynamically-linked
executables.  Statically-linked executables and foreign executables
running under binary emulation are not affected.

To tell whether or not B<sudo> supports I<noexec>, you can run
the following as root:

    # sudo -V | grep "dummy exec"

If the resulting output contains a line that begins with:

    File containing dummy exec functions

then B<sudo> may be able to replace the exec family of functions
in the standard library with its own that simply return an error.
Unfortunately, there is no foolproof way to know whether or not
I<noexec> will work at compile-time.  I<Noexec> should work on
SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX
11.x.  It is known B<not> to work on AIX and UnixWare.  I<Noexec>
is expected to work on most operating systems that support the
C<LD_PRELOAD> environment variable.  Check your operating system's
manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld,
dld.sl, rld, or loader) to see if C<LD_PRELOAD> is supported.

To enable I<noexec> for a command, use the C<NOEXEC> tag as documented
in the User Specification section above.  If you are unsure whether
or not your system is capable of supporting I<noexec> you can always
just try it out and see if it works.

=head1 CAVEATS

The I<sudoers> file should B<always> be edited by the B<visudo>
command which locks the file and does grammatical checking. It is
imperative that I<sudoers> be free of syntax errors since B<sudo>
will not run with a syntactically incorrect I<sudoers> file.

When using netgroups of machines (as opposed to users), if you
store fully qualified hostnames in the netgroup (as is usually the
case), you either need to have the machine's hostname be fully qualified
as returned by the C<hostname> command or use the I<fqdn> option in
I<sudoers>.

=head1 FILES

 @sysconfdir@/sudoers		List of who can run what
 /etc/group		Local groups file
 /etc/netgroup		List of network groups

=head1 SEE ALSO

rsh(1), su(1), fnmatch(3), sudo(8), visudo(8)