file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).
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).
grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
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 production rules
symbol ::= definition
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).
There are four kinds of 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]_)*
definition is of the form
Alias_Type NAME = item1, item2, ...
is one of
is a string of uppercase letters, numbers, and underscore characters (‘
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 (‘
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
is made up of one or more user names, user ids (prefixed with ‘
’), system group names and ids (prefixed with ‘
’ and ‘
’ respectively), netgroups (prefixed with ‘
’), non-Unix group names and IDs (prefixed with ‘
’ and ‘
’ respectively) and
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.
may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g. \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.
syntax depends on the underlying implementation. For instance, the QAS AD backend supports the following formats:
Group in the same domain: "%:Group Name"
Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
Note that quotes around group names are optional. Unquoted strings must use a backslash (‘
’) to escape spaces and special characters. See Other special characters and reserved words
for a list of characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
is similar to a
except that instead of
it can contain
. Note that user names 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 user names 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 ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
is made up of one or more host names, 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 host name may include shell-style wildcards (see the Wildcards
section below), but unless the
command on your machine returns the fully qualified host name, you'll need to use the fqdn
option for wildcards to be useful. Note that sudo
only inspects actual network interfaces; this means that IP address 127.0.0.1 (localhost) will never match. Also, the host name “localhost” will only match if that is the actual host name, which is usually only the case for non-networked systems.
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Cmnd ::= '!'* command name |
'!'* directory |
'!'* "sudoedit" |
is a list of one or more command names, directories, and other aliases. A command name is a fully qualified file name which may include shell-style wildcards (see the Wildcards
section below). A simple file name 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 path name ending in a ‘
’. When you specify a directory in a
, the user will be able to run any file within that directory (but not in any sub-directories therein).
has associated command line arguments, then the arguments in the
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 “
” 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.
Certain configuration options may be changed from their default values at run-time via one or more
lines. These may affect all users on any host, all users on a specific host, a specific user, a specific command, or commands being run as a specific user. Note that per-command entries may not include command line arguments. If you need to specify arguments, define a
and reference that instead.
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 |
Parameters may be flags
, 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,
. 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_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? SELinux_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |
'SETENV:' | 'NOSETENV:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' |
'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')
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.
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into its constituent parts:
determines the user and/or the group that a command may be run as. A fully-specified
consists of two
(as defined above) separated by a colon (‘
’) and enclosed in a set of parentheses. The first
indicates which users the command may be run as via sudo
option. The second defines a list of groups that can be specified via sudo
option. If both
are specified, the command may be run with any combination of users and groups listed in their respective
If only the first is specified, the command may be run as any user in the list but no -g
option may be specified. If the first
is empty but the second is specified, the command may be run as the invoking user with the group set to any listed in the
. If no
is specified the command may be run as root
and no group may be specified.
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
, and /usr/bin/lprm
but only as operator
$ sudo -u operator /bin/ls
It is also possible to override a
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
, but /bin/kill
We can extend this to allow dgb
with either the user or group set to operator
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
Note that while the group portion of the
permits the user to run as command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm
may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
Note that in this example only the group will be set, the command still runs as user tcm
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a
, in which case the user may select any combination of users and groups via the -u
options. In this example:
alan ALL = (root, bin : operator, system) ALL
may run any command as either user root or bin, optionally setting the group to operator or system.
SELinux_Spec On systems with SELinux support, sudoers entries may optionally have an SELinux role and/or type associated with a command. If a role or type is specified with the command it will override any default values specified in sudoers. A role or type specified on the command line, however, will supersede the values in sudoers.
A command may have zero or more tags associated with it. There are ten possible tag values:
. Once a tag is set on a
, inherit the tag unless it is overridden by the opposite tag (in other words,
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
tag. Like a
tag sets a default for the commands that follow it in the
. Conversely, the
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
, and /usr/bin/lprm
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
tag has no effect on users who are in the group specified by the exempt_group
By default, if the
tag is applied to any of the entries for a user on the current host, he or she will be able to run “
” without a password. Additionally, a user may only run “
” without a password if the
tag is present for all a user's entries that pertain to the current host. This behavior may be overridden via the verifypw
NOEXEC and EXEC
has been compiled with noexec
support and the underlying operating system supports it, the
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
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
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
has been set for a command, the user may disable the env_reset
option from the command line via the -E
option. Additionally, environment variables set on the command line are not subject to the restrictions imposed by env_check
, or env_keep
. As such, only trusted users should be allowed to set variables in this manner. If the command matched is ALL
tag is implied for that command; this default may be overridden by use of the
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input
option on a per-command basis. For more information, see the description of log_input
in the SUDOERS OPTIONS
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output
option on a per-command basis. For more information, see the description of log_output
in the SUDOERS OPTIONS
allows shell-style wildcards
(aka meta or glob characters) to be used in host names, path names and command line arguments in the sudoers
file. Wildcard matching is done via the POSIX glob(3)
routines. Note that these are not
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.
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)
functions support them. However, because the ‘
’ character has special meaning in sudoers
, it must be escaped. For example:
Would match any file name beginning with a letter.
Note that a forward slash (‘
’) will not
be matched by wildcards used in the path name. This is to make a path like:
but not /usr/bin/X11/xterm
When matching the command line arguments, however, a slash does
get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care. Because command line arguments are matched as a single, concatenated string, a wildcard such as ‘
’ or ‘
’ can match multiple words. For example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended.
Exceptions to wildcard rules
The following exceptions apply to the above 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.
Command line arguments to the sudoedit built-in command should always be path names, so a forward slash (‘
/’) will not be matched by a wildcard.
Including other files from within sudoers
It is possible to include other sudoers
files from within the sudoers
file currently being parsed using the
This can be used, for example, to keep a site-wide sudoers
file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers
will be /etc/sudoers
and the per-machine one will be /etc/sudoers.local
. To include /etc/sudoers.local
from within /etc/sudoers
we would use the following line in /etc/sudoers
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.
If the path to the include file is not fully-qualified (does not begin with a ‘
’, it must be located in the same directory as the sudoers file it was included from. For example, if /etc/sudoers
contains the line:
the file that will be included is /etc/sudoers.local
The file name may also include the
escape, signifying the short form of the host name. In other words, if the machine's host name is “xerxes”, then
will cause sudo
to include the file /etc/sudoers.xerxes
directive can be used to create a sudo.d
directory that the system package manager can drop sudoers
rules into as part of package installation. For example, given:
will read each file in /etc/sudoers.d
, skipping file names that end in ‘
’ or contain a ‘
’ character to avoid causing problems with package manager or editor temporary/backup files. Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first
will be parsed before /etc/sudoers.d/10_second
. Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops
would be loaded after /etc/sudoers.d/10_second
. Using a consistent number of leading zeroes in the file names can be used to avoid such problems.
Note that unlike files included via
will not edit the files in a
directory unless one of them contains a syntax error. It is still possible to run visudo
with the -f
flag to edit the files directly.
Other special characters and reserved words
The pound sign (‘
’) is used to indicate a comment (unless it is part of a #include directive or 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 ALL
is a built-in alias
that always causes a match to succeed. It can be used wherever one might otherwise use a
. You should not try to define your own alias
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
. 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
Long lines can be continued with a backslash (‘
’) as the last character on the line.
White space 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 user name or host name): ‘
Below are example sudoers
entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases
Defaults env_keep += "DISPLAY HOME"
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBMASTERS = will, wendy, wim
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 220.127.116.11/255.255.0.0
Host_Alias CSNETS = 18.104.22.168, 22.214.171.124/24, 126.96.36.199
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
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,\
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
environment variables when running commands as root. Additionally, on the machines in the SERVERS
, 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
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
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
, and dowdy
) may run any command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley
, and crawl
) may run any command on any host but they must authenticate themselves first (since the entry lacks the
jack CSNETS = ALL
The user jack
may run any command on the machines in the CSNETS
alias (the networks
). Of those networks, only
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
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
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)
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers
group may run commands in /usr/sbin/
as themselves with any group in the ADMINGRP
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 user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob
may run anything on the SPARC
machines as any user listed in the OP
jim +biglab = ALL
The user jim
may run any command on machines in the biglab
knows that “biglab” is a netgroup due to the ‘
+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
) 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)
jen ALL, !SERVERS = ALL
The user jen
may run any command on any machine except for those in the SERVERS
(master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS
may run any commands in the directory /usr/bin/
except for those commands belonging to the SU
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
(will, wendy, and wim), may run any command as user www (which owns the web pages) or simply su(1)
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuidnodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
(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.