policy plugin determines a user's sudo
privileges. It is the default sudo
policy plugin. The policy is driven by the /etc/sudoers
file or, optionally in LDAP. The policy format is described in detail in the SUDOERS FILE FORMAT
section. For information on storing sudoers
policy information in LDAP, please see sudoers.ldap(5)
Configuring sudo.conf for sudoers sudo
consults the sudo.conf(5)
file to determine which policy and and I/O logging plugins to load. If no sudo.conf(5)
file is present, or if it contains no
will be used for policy decisions and I/O logging. To explicitly configure sudo.conf(5)
to use the sudoers
plugin, the following configuration can be used.
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo
1.8.5, it is possible to specify optional arguments to the sudoers
plugin in the sudo.conf(5)
file. These arguments, if present, should be listed after the path to the plugin (i.e. after sudoers.so
). Multiple arguments may be specified, separated by white space. For example:
Plugin sudoers_policy sudoers.so sudoers_mode=0400
The following plugin arguments are supported:
The ldap_conf argument can be used to override the default path to the ldap.conf file.
The ldap_secret argument can be used to override the default path to the ldap.secret file.
The sudoers_file argument can be used to override the default path to the sudoers file.
The sudoers_uid argument can be used to override the default owner of the sudoers file. It should be specified as a numeric user ID.
The sudoers_gid argument can be used to override the default group of the sudoers file. It must be specified as a numeric group ID (not a group name).
The sudoers_mode argument can be used to override the default file mode for the sudoers file. It should be specified as an octal value.
For more information on configuring sudo.conf(5)
, please refer to its manual.
Authentication and logging
security policy requires that most users authenticate themselves before they can use sudo
. A password is not required if the invoking user is root, if the target user is the same as the invoking user, or if the policy has disabled authentication for the user or command. Unlike su(1)
, when sudoers
requires authentication, it validates the invoking user's credentials, not the target user's (or root's) credentials. This can be changed via the rootpw
flags, described later.
If a user who is not listed in the policy tries to run a command via sudo
, mail is sent to the proper authorities. The address used for such mail is configurable via the mailto
Defaults entry (described later) and defaults to
Note that no mail will be sent if an unauthorized user tries to run sudo
with the -l
option unless there is an authentication error and either the mail_always
flags are enabled. This allows users to determine for themselves whether or not they are allowed to use sudo
. All attempts to run sudo
(successful or not) will be logged, regardless of whether or not mail is sent.
is run by root and the SUDO_USER
environment variable is set, the sudoers
policy will use this value to determine who the actual user is. This can be used by a user to log commands through sudo even when a root shell has been invoked. It also allows the -e
option to remain useful even when invoked via a sudo-run script or program. Note, however, that the sudoers
lookup is still done for root, not the user specified by SUDO_USER
uses per-user time stamp files for credential caching. Once a user has been authenticated, a record is written containing the uid that was used to authenticate, the terminal session ID, and a time stamp (using a monotonic clock if one is available). The user may then use sudo
without a password for a short period of time (
minutes unless overridden by the timeout
option). By default, sudoers
uses a separate record for each tty, which means that a user's login sessions are authenticated separately. The tty_tickets
option can be disabled to force the use of a single time stamp for all of a user's sessions.
can log both successful and unsuccessful attempts (as well as errors) to syslog(3)
, a log file, or both. By default, sudoers
will log via syslog(3)
but this is changeable via the syslog
also supports logging a command's input and output streams. I/O logging is not on by default but can be enabled using the log_input
Defaults flags as well as the
Since environment variables can influence program behavior, sudoers
provides a means to restrict which variables from the user's environment are inherited by the command to be run. There are two distinct ways sudoers
can deal with environment variables.
By default, the env_reset
option is enabled. This causes commands to be executed with a new, minimal environment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of the /etc/environment
file. On BSD systems, if the use_loginclass
option is enabled, the environment is initialized based on the path
settings in /etc/login.conf
. The new environment contains the TERM
variables in addition to variables from the invoking process permitted by the env_check
options. This is effectively a whitelist for environment variables. Environment variables with a value beginning with
are removed unless both the name and value parts are matched by env_keep
, as they will be interpreted as functions by older versions of the bash
shell. Prior to version 1.8.11, such variables were always removed.
If, however, the env_reset
option is disabled, any variables not explicitly denied by the env_check
options are inherited from the invoking process. In this case, env_check
behave like a blacklist. Environment variables with a value beginning with
are always removed, even if they do not match one of the blacklists. Since it is not possible to blacklist all potentially dangerous environment variables, use of the default env_reset
behavior is encouraged.
By default, environment variables are matched by name. However, if the pattern includes an equal sign (‘
’), both the variables name and value must match. For example, an old-style (pre-shellshock) bash
shell function could be matched as follows:
env_keep += "my_func=()*"
Without the “
” suffix, this would not match, as old-style bash
shell functions are not preserved by default.
The complete list of environment variables that sudo
allows or denies is contained in the output of “
” when run as root. Please note that this list varies based on the operating system sudo
is running on.
On systems that support PAM where the pam_env
module is enabled for sudo
, variables in the PAM environment may be merged in to the environment. If a variable in the PAM environment is already present in the user's environment, the value will only be overridden if the variable was not preserved by sudoers
. When env_reset
is enabled, variables preserved from the invoking user's environment by the env_keep
list take precedence over those in the PAM environment. When env_reset
is disabled, variables present the invoking user's environment take precedence over those in the PAM environment unless they match a pattern in the env_delete
Note that the dynamic linker on most operating systems will remove variables that can control dynamic linking from the environment of setuid executables, including sudo
. Depending on the operating system this may include _RLD*
, and others. These type of variables are removed from the environment before sudo
even begins execution and, as such, it is not possible for sudo
to preserve them.
As a special case, if sudo
option (initial login) is specified, sudoers
will initialize the environment regardless of the value of env_reset
. The DISPLAY
variables remain unchanged; HOME
, and LOGNAME
are set based on the target user. On AIX (and Linux systems without PAM), the contents of /etc/environment
are also included. On BSD systems, if the use_loginclass
flag is enabled, the path
variables in /etc/login.conf
are also applied. All other environment variables are removed.
Finally, if the env_file
option is defined, any variables present in that file will be set to their specified values as long as they would not conflict with an existing environment variable.
SUDOERS FILE FORMAT
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
It is a syntax error to redefine an existing alias
. It is possible to use the same name for aliases
of different types, but this is not recommended.
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
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.
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 group provider plugin. For instance, the QAS AD plugin 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"
See GROUP PROVIDER PLUGINS
for more information.
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
es it can contain
es. 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.
digest ::= [A-Fa-f0-9]+ |
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Cmnd ::= Digest_Spec? '!'* 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 built-in 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. Note that “
” is a command built into sudo
itself and must be specified in sudoers
without a leading path.
is prefixed with a
, the command will only match successfully if it can be verified using the specified SHA-2 digest. This may be useful in situations where the user invoking sudo
has write access to the command or its parent directory. The following digest formats are supported: sha224, sha256, sha384 and sha512. The string may be specified in either hex or base64 format (base64 is more compact). There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
Command digests are only supported by version 1.8.7 or higher.
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? Solaris_Priv_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Solaris_Priv_Spec ::= ('PRIVS=privset' | 'LIMITPRIVS=privset')
Tag_Spec ::= ('NOEXEC:' | 'EXEC:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' |
'LOG_OUTPUT:' | 'NOLOG_OUTPUT:' | 'MAIL:' | 'NOMAIL:' |
'NOPASSWD:' | 'PASSWD:' | '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.
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
s (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
s are specified, the command may be run with any combination of users and groups listed in their respective
s. 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 both
s are empty, the command may only be run as the invoking user. 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.
On Solaris systems, sudoers
entries may optionally specify Solaris privilege set and/or limit privilege set associated with a command. If privileges or limit privileges are specified with the command it will override any default values specified in sudoers
A privilege set is a comma-separated list of privilege names. The ppriv(1)
command can be used to list all privileges known to the system. For example:
$ ppriv -l
In addition, there are several “special” privilege strings:
the empty set
the set of all privileges
the set of all privileges available in the current zone
the default set of privileges normal users are granted at login time
Privileges can be excluded from a set by prefixing the privilege name with either an ‘
’ or ‘
A command may have zero or more tags associated with it. There are ten possible tag values:
. Once a tag is set on a
s in the
, inherit the tag unless it is overridden by the opposite tag (in other words,
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.
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 section below.
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 section below.
These tags provide fine-grained control over whether mail will be sent when a user runs a command by overriding the value of the mail_all_cmnds option on a per-command basis. They have no effect when sudo is run with the -l or -v options. A NOMAIL tag will also override the mail_always and mail_no_perms options. For more information, see the descriptions of mail_all_cmnds, mail_always, and mail_no_perms in the SUDOERS OPTIONS section below.
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
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.
These tags override the value of the setenv option on a per-command basis. Note that if
SETENV 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, 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
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 glob(3)
functions as specified by IEEE Std 1003.1 (“POSIX.1”). 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 ‘
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 sudoers.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, but this will not catch the redefinition of an alias
that is also present in a different file.
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 in a list or alias
as well as in front of a
. This allows one to exclude certain values. For the ‘
’ operator to be effective, there must be something for it to exclude. For example, to match all users except for root one would use:
If the ALL
, is omitted, as in:
it would explicitly deny root but not match any other users. This is different from a true “negation” operator.
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
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Note that other programs use HOME to find
# configuration files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# 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
Runas_Alias ADMINGRP = adm, oper
# 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 = 126.96.36.199/255.255.0.0
Host_Alias CSNETS = 188.8.131.52, 184.108.40.206/24, 220.127.116.11
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,\
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
). Note that this will not effectively constrain users with sudo ALL
# Override built-in defaults
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/
. Note that one command in the
Cmnd_Alias includes a sha224 digest, /home/operator/bin/start_backups
. This is because the directory containing the script is writable by the operator user. If the script is modified (resulting in a digest mismatch) it will no longer be possible to run it via sudo
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
. While not specifically mentioned in the rule, the commands in the PAGERS
all reside in /usr/bin
and have the noexec
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 nosuid,nodev /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.
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from 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 bill
from running the commands listed in SU
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).
In general, if a user has sudo ALL
there is nothing to prevent them from creating their own program that gives them a root shell (or making their own copy of a shell) regardless of any ‘
’ elements in the user specification.
Security implications of fast_glob
If the fast_glob
option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3)
function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges.
For example, given the following sudoers
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
can still run
is enabled by changing to /usr/bin
Preventing shell escapes
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 sudo
's access control and logging. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs.
There are two basic approaches to this problem:
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 is often unworkable.
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.
The noexec feature is known to work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, HP-UX 11.x and AIX 5.3 and above. It should be supported 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.
On Solaris 10 and higher, noexec uses Solaris privileges instead of the LD_PRELOAD environment variable.
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 check whether shell escapes work when noexec is enabled.
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
plugin includes sudoedit
support which allows users to securely edit files with the editor of their choice. As sudoedit
is a built-in command, it must be specified in sudoers
without a leading path. However, it may take command line arguments just as a normal command does. Wildcards used in sudoedit
command line arguments are expected to be path names, so a forward slash (‘
’) will not be matched by a wildcard.
Unlike other sudo
commands, the editor is run with the permissions of the invoking user and with the environment unmodified. More information may be found in the description of the -e
option in sudo(8)
For example, to allow user operator to edit the “message of the day” file:
operator sudoedit /etc/motd
The operator user then runs sudoedit
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of /etc/motd
. After the file has been edited, /etc/motd
will be updated with the contents of the temporary copy.
Time stamp file checks sudoers
will check the ownership of its time stamp directory (/var/run/sudo/ts
by default) and ignore the directory's contents if it is not owned by root or if it is writable by a user other than root. Older versions of sudo
stored time stamp files in /tmp
; this is no longer recommended as it may be possible for a user to create the time stamp themselves on systems that allow unprivileged users to change the ownership of files they create.
While the time stamp directory should
be cleared at reboot time, not all systems contain a /var/run
directory. To avoid potential problems, sudoers
will ignore time stamp files that date from before the machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow unprivileged users to change the system clock. Since sudoers
relies on the system clock for time stamp validation, it may be possible on such systems for a user to run sudo
for longer than timestamp_timeout
by setting the clock back. To combat this, sudoers
uses a monotonic clock (which never moves backwards) for its time stamps if the system supports it.
will not honor time stamps set far in the future. Time stamps with a date greater than current_time + 2 *
will be ignored and sudoers
will log and complain.
Since time stamp files live in the file system, they can outlive a user's login session. As a result, a user may be able to login, run a command with sudo
after authenticating, logout, login again, and run sudo
without authenticating so long as the record's time stamp is within
minutes (or whatever value the timeout is set to in sudoers
). When the tty_tickets
option is enabled, the time stamp record includes the device number of the terminal the user authenticated with. This provides per-tty granularity but time stamp records still may outlive the user's session. The time stamp record also includes the session ID of the process that last authenticated. This prevents processes in different terminal sessions from using the same time stamp record. It also helps reduce the chance that a user will be able to run sudo
without entering a password when logging out and back in again on the same terminal.