SUDOERS

NAME

DESCRIPTION

When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).

The sudoers grammar 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.  

Quick guide to EBNF

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

Each 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.

?

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

*

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

+

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

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).  

Aliases

 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 alias definition is of the form

 Alias_Type NAME = item1, item2, ...

where Alias_Type is one of User_Alias
, Runas_Alias
, Host_Alias
, or Cmnd_Alias
. A NAME
is a string of uppercase letters, numbers, and underscore characters ('_'). A NAME
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 alias member follow.

 User_List ::= User |
               User ',' User_List

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

A User_List
is made up of one or more usernames, uids (prefixed with '#'), system groups (prefixed with '%'), netgroups (prefixed with '+') and User_Alias
es. Each list item may be prefixed with zero 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_Member |
                Runas_Member ',' Runas_List

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

A Runas_List
is similar to a User_List
except that instead of User_Alias
es it can contain Runas_Alias
es. Note that usernames and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are considered to be distinct. If you wish to match all usernames with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given).

 Host_List ::= Host |
               Host ',' Host_List

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

A 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 along with the network number, sudo will query each of the local host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may be specified either in standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g. 24 or 64). A hostname may include shell-style wildcards (see the Wildcards section below), but unless the hostname
command on your machine returns the fully qualified hostname, you'll need to use the 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 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 the 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 "" to indicate that the command may only be run without command line arguments. A directory is a fully qualified pathname ending in a '/'. When you specify a directory in a Cmnd_List
, the user will be able to run any file within that directory (but not in any subdirectories therein).

If a Cmnd
has associated command line arguments, then the arguments in the 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 "sudoedit" is used to permit a user to run sudo with the -e option (or as sudoedit). It may take command line arguments just as a normal command does.  

Defaults

 Default_Type ::= 'Defaults' |
                  'Defaults' '@' Host_List |
                  'Defaults' ':' User_List |
                  'Defaults' '!' Cmnd_List |
                  'Defaults' '>' Runas_List

 Default_Entry ::= Default_Type Parameter_List

 Parameter_List ::= Parameter |
                    Parameter ',' Parameter_List

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

Parameters may be flags, integer values, strings, or 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 ( "
) when they contain multiple words. Special characters may be escaped with a backslash ( \
).

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

Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas Defaults and finally command defaults.

See ``SUDOERS OPTIONS'' for a list of supported Defaults parameters.  

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? (: Runas_List)? ')'

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

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

Let's break that down into its constituent parts:  

Runas_Spec

A Runas_Spec
sets the default for the commands that follow it. What this means is that for the entry:

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

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

 $ sudo -u operator /bin/ls.

It is also possible to override a 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 dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.

We can extend this to allow dgb to run /bin/ls
with either the user or group set to operator:

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

In the following example, user tcm may run commands that access a modem device file with the dialer group. Note that in this example only the group will be set, the command still runs as user tcm.

 tcm    boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \
        /usr/local/bin/minicom

Tag_Spec

NOPASSWD and PASSWD

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

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

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

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

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

By default, if the NOPASSWD
tag is applied to any of the entries for a user on the current host, he or she will be able to run sudo -l
without a password. Additionally, a user may only run sudo -v
without a password if the 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.

NOEXEC and EXEC

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

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

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

See the ``PREVENTING SHELL ESCAPES'' section below for more details on how NOEXEC
works and whether or not it will work on your system.

SETENV and NOSETENV

These tags override the value of the setenv option on a per-command basis. Note that if SETENV
has been set for a command, any environment variables set on the command line way are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. If the command matched is ALL, the SETENV
tag is implied for that command; this default may be overridden by use of the UNSETENV
tag.  

Wildcards

*

Matches any set of zero or more characters.

?

Matches any single character.

[...]

Matches any character in the specified range.

[!...]

Matches any character not in the specified range.

\x

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

POSIX character classes may also be used if your system's glob(3) and fnmatch(3) functions support them. However, because the ':' character has special meaning in sudoers, it must be escaped. For example:

    /bin/ls [[\:alpha\:]]*

Would match any filename beginning with a letter.

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

    /usr/bin/*

match /usr/bin/who but not /usr/bin/X11/xterm.  

Exceptions to wildcard rules

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

Including other files from within sudoers

#include /etc/sudoers.local

When sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops.

The filename may include the %h escape, signifying the short form of the hostname. I.e., if the machine's hostname is ``xerxes'', then

 #include /etc/sudoers.%h

will cause sudo to include the file /etc/sudoers.xerxes.  

Other special characters and reserved words

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

An exclamation point ('!') can be used as a logical not operator both in an alias and in front of a Cmnd
. This allows one to exclude certain values. Note, however, that using a !
in conjunction with the built-in 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 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): '@', '!', '=', ':', ',', '(', ')', '\'.  

SUDOERS OPTIONS

Flags:

always_set_home

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

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 PASSWD
and NOPASSWD
tags. This flag is on by default.

closefrom_override

If set, the user may use sudo's -C option which overrides the default starting point at which sudo begins closing open file descriptors. This flag is off by default.

env_editor

If set, 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 editor
variable. visudo will then only use the EDITOR or VISUAL if they match a value specified in editor
. This flag is on by default.

env_reset

If set, sudo will reset the environment to only contain the LOGNAME, SHELL, USER, USERNAME and the SUDO_*
variables. Any variables in the caller's environment that match the env_keep
and env_check
lists are then added. The default contents of the env_keep
and env_check
lists are displayed when sudo is run by root with the -V option. If the secure_path option is set, its value will be used for the PATH
environment variable. This flag is on by default.

fqdn

Set this flag if you want to put fully qualified hostnames in the 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 fqdn requires sudo to make DNS lookups which may make 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 ( 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 hostname
command) is already fully qualified you shouldn't need to set fqdn. This flag is off by default.

ignore_dot

If set, sudo will ignore '.' or '' (current dir) in the PATH
environment variable; the PATH
itself is not modified. This flag is on by default.

ignore_local_sudoers

If set via LDAP, parsing of /etc/sudoers will be skipped. This is intended for Enterprises that wish to prevent the usage of local sudoers files so that only LDAP is used. This thwarts the efforts of rogue operators who would attempt to add roles to /etc/sudoers. When this option is present, /etc/sudoers does not even need to exist. Since this option tells sudo how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the cn=defaults
section. This flag is off by default.

insults

If set, sudo will insult users when they enter an incorrect password. This flag is off by default.

log_host

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

log_year

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

long_otp_prompt

When validating with a One Time Password (OPT) scheme such as S/Key or 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 off by default.

mail_always

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

mail_badpass

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

mail_no_host

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

mail_no_perms

If set, mail will be sent to the mailto user if the invoking user is allowed to use sudo but the command they are trying is not listed in their sudoers file entry or is explicitly denied. This flag is off by default.

mail_no_user

If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file. This flag is on by default.

noexec

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

path_info

Normally, sudo will tell the user when a command could not be found in their 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 PATH
, sudo will tell the user that they are not allowed to run it, which can be confusing. This flag is on by default.

passprompt_override

The password prompt specified by passprompt will normally only be used if the passwod prompt provided by systems such as PAM matches the string ``Password:''. If passprompt_override is set, passprompt will always be used. This flag is off by default.

preserve_groups

By default, sudo will initialize the group vector to the list of groups the target user is in. When 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 off by default.

pwfeedback

By default, sudo reads the password like most other Unix programs, by turning off echo until the user hits the return (or enter) key. Some users become confused by this as it appears to them that sudo has hung at this point. When pwfeedback is set, sudo will provide visual feedback when the user presses a key. Note that this does have a security impact as an onlooker may be able to determine the length of the password being entered. This flag is off by default.

requiretty

If set, sudo will only run when the user is logged in to a real tty. When this flag is set, sudo can only be run from a login session and not via other means such as cron(8) or cgi-bin scripts. This flag is off by default.

root_sudo

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

rootpw

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

runaspw

If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to root
) instead of the password of the invoking user. This flag is off by default.

set_home

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

set_logname

Normally, sudo will set the LOGNAME
, USER
and USERNAME
environment variables to the name of the target user (usually root unless the -u option is given). However, since some programs (including the RCS revision control system) use 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. Note that if the env_reset option has not been disabled, entries in the env_keep list will override the value of set_logname. This flag is off by default.

setenv

Allow the user to disable the env_reset option from the command line. Additionally, environment variables set via the command line are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. This flag is off by default.

shell_noargs

If set and sudo is invoked with no arguments it acts as if the -s option had been given. That is, it runs a shell as root (the shell is determined by the 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 off by default.

fast_glob

Normally, sudo uses the glob(3) function to do shell-style globbing when matching pathnames. However, since it accesses the file system, glob(3) can take a long time to complete for some patterns, especially when the pattern references a network file system that is mounted on demand (automounted). The fast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do its matching. The disadvantage of fast_glob is that it is unable to match relative pathnames such as ./ls or ../bin/ls. This flag is off by default.

stay_setuid

Normally, when 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 sudo act as a setuid wrapper. This can be useful on systems that disable some potentially dangerous functionality when a program is run setuid. This option is only effective on systems with either the setreuid() or setresuid() function. This flag is off by default.

targetpw

If set, sudo will prompt for the password of the user specified by the -u option (defaults to root
) instead of the password of the invoking user. Note that this precludes the use of a uid not listed in the passwd database as an argument to the -u option. This flag is off by default.

tty_tickets

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

umask_override

If set, sudo will set the umask as specified by sudoers without modification. This makes it possible to specify a more permissive umask in sudoers than the user's own umask and matches historical behavior. If umask_override is not set, sudo will set the umask to be the union of the user's umask and what is specified in sudoers. This flag is off by default.

visiblepw

By default, sudo will refuse to run if the user must enter a password but it is not possible to disable echo on the terminal. If the visiblepw flag is set, sudo will prompt for a password even when it would be visible on the screen. This makes it possible to run things like "rsh somehost sudo ls" since rsh(1) does not allocate a tty. This flag is off by default.

Integers:

closefrom

Before it executes a command, sudo will close all open file descriptors other than standard input, standard output and standard error (ie: file descriptors 0-2). The closefrom option can be used to specify a different file descriptor at which to start closing. The default is 3.

passwd_tries

The number of tries a user gets to enter his/her password before sudo logs the failure and exits. The default is 3
.

Integers that can be used in a boolean context:

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 80
(use 0 or negate the option to disable word wrap).

passwd_timeout

Number of minutes before the sudo password prompt times out. The default is 5
; set this to 0 for no password timeout.

timestamp_timeout

Number of minutes that can elapse before sudo will ask for a passwd again. The default is 5
. Set this to 0 to always prompt for a password. If set to a value less than 0 the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via sudo -v
and sudo -k
respectively.

umask

Umask to use when running the command. Negate this option or set it to 0777 to preserve the user's umask. The actual umask that is used will be the union of the user's umask and 0022
. This guarantees that sudo never lowers the umask when running a command. Note on systems that use PAM, the default PAM configuration may specify its own umask which will override the value set in sudoers.

Strings:

badpass_message

Message that is displayed if a user enters an incorrect password. The default is Sorry, try again.
unless insults are enabled.

editor

A colon (':') separated list of editors allowed to be used with visudo. visudo will choose the editor that matches the user's EDITOR 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.

mailsub

Subject of the mail sent to the mailto user. The escape %h will expand to the hostname of the machine. Default is *** SECURITY information for %h ***
.

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 noexec functionality on systems that support LD_PRELOAD
or its equivalent. Defaults to /usr/libexec/sudo_noexec.so.

passprompt

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

%H

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

%h

expanded to the local hostname without the domain name

%p

expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)

%U

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

%u

expanded to the invoking user's login name

%%

two consecutive %
characters are collapsed into a single %
character

The default value is [sudo] password for %p:
.

role

The default SELinux role to use when constructing a new security context to run the command. The default role may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.

runas_default

The default user to run commands as if the -u option is not specified on the command line. This defaults to root
. Note that if runas_default is set it must occur before any Runas_Alias
specifications.

syslog_badpri

Syslog priority to use when user authenticates unsuccessfully. Defaults to alert
.

syslog_goodpri

Syslog priority to use when user authenticates successfully. Defaults to notice
.

sudoers_locale

Locale to use when parsing the sudoers file. Note that changing the locale may affect how sudoers is interpreted. Defaults to "C".

timestampdir

The directory in which sudo stores its timestamp files. The default is /var/run/sudo.

timestampowner

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

type

The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.

Strings that can be used in a boolean context:

askpass

The askpass option specifies the fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when sudo is executed from a graphical (as opposed to text-based) application. The program specified by askpass should display the argument passed to it as the prompt and write the user's password to the standard output. The value of askpass may be overridden by the SUDO_ASKPASS
environment variable.

env_file

The env_file options specifies the fully qualified path to a file containing variables to be set in the environment of the program being run. Entries in this file should be of the form VARIABLE=value
. Variables in this file are subject to other sudo environment settings such as env_keep and env_check.

exempt_group

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

lecture

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

always

Always lecture the user.

never

Never lecture the user.

once

Only lecture the user the first time they run sudo.

If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is once.

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. By default, sudo uses a built-in lecture.

listpw

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

all

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

always

The user must always enter a password to use the -l option.

any

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

never

The user need never enter a password to use the -l option.

If no value is specified, a value of any is implied. Negating the option results in a value of never being used. The default value is any.

logfile

Path to the sudo log file (not the syslog log file). Setting a path turns on logging to a file; negating this option turns it off. By default, sudo logs via syslog.

mailerflags

Flags to use when invoking mailer. Defaults to -t.

mailerpath

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

mailfrom

Address to use for the ``from'' address when sending warning and error mail. The address should be enclosed in double quotes ( "
) to protect against sudo interpreting the @
sign. Defaults to the name of the user running sudo.

mailto

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

secure_path

Path used for every command run from sudo. If you don't trust the people running sudo to have a sane PATH
environment variable you may want to use this. Another use is if you want to have the ``root path'' be separate from the ``user path.'' Users in the group specified by the exempt_group option are not affected by secure_path. This is not set by default.

syslog

Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to authpriv
.

verifypw

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

all

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

always

The user must always enter a password to use the -v option.

any

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

never

The user need never enter a password to use the -v option.

If no value is specified, a value of all is implied. Negating the option results in a value of never being used. The default value is all.

Lists that can be used in a boolean context:

env_check

Environment variables to be removed from the user's environment if the variable's value contains %
or /
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 =
, +=
, -=
, and !
operators respectively. Regardless of whether the env_reset
option is enabled or disabled, variables specified by env_check
will be preserved in the environment if they pass the aforementioned check. The default list of environment variables to check is displayed when sudo is run by root with the -V option.

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 =
, +=
, -=
, and !
operators respectively. The default list of environment variables to remove is displayed when sudo is run by root with the -V option. Note that many operating systems will remove potentially dangerous variables from the environment of any setuid process (such as sudo).

env_keep

Environment variables to be preserved in the user's environment when the env_reset option is in effect. This allows fine-grained control over the environment 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 =
, +=
, -=
, and !
operators respectively. The default list of variables to keep is displayed when sudo is run by root with the -V option.

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

FILES

/etc/sudoers

List of who can run what

/etc/group

Local groups file

/etc/netgroup

List of network groups

EXAMPLES

 # 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
 Cmnd_Alias     REBOOT = /usr/sbin/reboot
 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
 Cmnd_Alias     PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less

Here we override some of the compiled in default values. We want sudo to log via syslog(3) using the auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user millert need not give a password, and we don't want to reset the LOGNAME
, USER
or USERNAME
environment variables when running commands as root. Additionally, on the machines in the SERVERS 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. Lastly, we disable shell escapes for the commands in the PAGERS Cmnd_Alias
(/usr/bin/more, /usr/bin/pg and /usr/bin/less).

 # 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
 Defaults!PAGERS        noexec

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

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

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

 FULLTIMERS     ALL = NOPASSWD: ALL

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

 PARTTIMERS     ALL = ALL

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

 jack           CSNETS = ALL

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

 lisa           CUNETS = ALL

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

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

The 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 /usr/oper/bin/.

 joe            ALL = /usr/bin/su operator

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

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

The user pete is allowed to change anyone's password except for root on the 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 bob may run anything on the SPARC and SGI machines as any user listed in the OP Runas_Alias
(root and operator).

 jim            +biglab = ALL

The user jim may run any command on machines in the biglab netgroup. sudo knows that ``biglab'' is a netgroup due to the '+' prefix.

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

Users in the 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 fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.

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

On the ALPHA machines, user john may su to anyone except root but he is not allowed to specify any options to the su(1) command.

 jen            ALL, !SERVERS = ALL

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

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

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

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

The user 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, 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 WEBMASTERS 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 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.  

SECURITY NOTES

    bill        ALL = ALL, !SU, !SHELLS

Doesn't really prevent bill from running the commands listed in SU or 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).  

PREVENTING SHELL ESCAPES

There are two basic approaches to this problem:

restrict

Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though sudoedit is a better solution to running editors via sudo. Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not if often unworkable.

noexec

Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually LD_PRELOAD
) to an alternate shared library. On such systems, sudo's 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 sudo supports 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 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 noexec will work at compile-time. noexec should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known not to work on AIX and UnixWare. noexec is expected to work on most operating systems that support the 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 LD_PRELOAD
is supported.

To enable noexec for a command, use the NOEXEC
tag as documented in the User Specification section above. Here is that example again:

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

This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and see if it works.

Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer approach is to give the user permission to run sudoedit.  

SEE ALSO

CAVEATS

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 hostname
command or use the fqdn option in sudoers.  

BUGS

SUPPORT

DISCLAIMER