sudoers — default sudo security policy module at Linux.org

Back to main site | Back to man page index

SUDOERS(5) BSD File Formats Manual SUDOERS(5)

NAME
sudoers — default sudo security policy module

DESCRIPTION

The sudoers policy module determines a user's sudo privileges. It is the default sudo policy plugin. The pol‐
icy 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).

Authentication and logging
The sudoers security policy requires that most users authenticate themselves before they can use sudo. A pass‐
word 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 authentica‐
tion, it validates the invoking user's credentials, not the target user's (or root's) credentials. This can be
changed via the rootpw, targetpw and runaspw 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 authori‐
ties. The address used for such mail is configurable via the mailto Defaults entry (described later) and
defaults to root.

Note that mail will not be sent if an unauthorized user tries to run sudo with the -l or -v option. This allows
users to determine for themselves whether or not they are allowed to use sudo.

If sudo 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.

sudoers uses time stamp files for credential caching. Once a user has been authenticated, the time stamp is
updated and the user may then use sudo without a password for a short period of time (5 minutes unless
overridden by the timeout option). By default, sudoers uses a tty-based time stamp which means that there is a
separate time stamp for each of a user's login sessions. The tty_tickets option can be disabled to force the
use of a single time stamp for all of a user's sessions.

sudoers 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 and logfile Defaults settings.

sudoers 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 and log_output Defaults flags as well as the LOG_INPUT and LOG_OUTPUT command tags.

Command environment
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 environ‐
ment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of the
/etc/environment file. The new environment contains the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER, USERNAME
and SUDO_* variables in addition to variables from the invoking process permitted by the env_check and env_keep
options. This is effectively a whitelist for environment variables.

If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and
env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave like
a blacklist. Since it is not possible to blacklist all potentially dangerous environment variables, use of the
default env_reset behavior is encouraged.

In all cases, environment variables with a value beginning with () are removed as they could be interpreted as
bash functions. The list of environment variables that sudo allows or denies is contained in the output of
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
The sudoers 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).

The sudoers grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfa‐
miliar 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. E.g.,

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

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

User_Alias ::= NAME '=' User_List

Runas_Alias ::= NAME '=' Runas_List

Host_Alias ::= NAME '=' Host_List

Cmnd_Alias ::= NAME '=' Cmnd_List

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

Each alias definition is of the form

A User_List is made up of one or more user names, user ids (prefixed with ‘#’), system group names and ids (pre‐
fixed with ‘%’ and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix group names and IDs (prefixed
with ‘%:’ and ‘%:#’ respectively) and User_Aliases. Each list item may be prefixed with zero or more ‘!’ opera‐
tors. An odd number of ‘!’ operators negate the value of the item; an even number just cancel each other out.

A user name, uid, group, gid, netgroup, nonunix_group or nonunix_gid 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.

The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin (see the
group_plugin description below). For instance, the QAS AD plugin supports the following formats:

· Group in the same domain: "%:Group Name"

· Group in any domain: "%:Group [email protected]"

· 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

A Runas_List is similar to a User_List except that instead of User_Aliases it can contain Runas_Aliases. 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)? |

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]+ |
[[A-Za-z0-9+/=]+

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" |
'!'* Cmnd_Alias

A Cmnd_List 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 spec‐
ify a directory in a Cmnd_List, the user will be able to run any file within that directory (but not in any sub-
directories 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.

If a command name is prefixed with a Digest_Spec, the command will only match successfully if it can be verified
using the specified SHA-2 digest. 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
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25

It is also possible to use openssl to generate base64 output:

$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==

If the user has write access to either the command itself or the directory in which the command is located

'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? SELinux_Spec? Tag_Spec* Cmnd

Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'

SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')

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:

Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be run as. A fully-specified Runas_Spec
consists of two Runas_Lists (as defined above) separated by a colon (‘:’) and enclosed in a set of parentheses.
The first Runas_List indicates which users the command may be run as via sudo's -u option. The second defines a

$ 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

Note that while the group portion of the Runas_Spec 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,\
/usr/local/bin/minicom

Note that in this example only the group will be set, the command still runs as user tcm. E.g.

$ sudo -g dialer /usr/bin/cu

Multiple users and groups may be present in a Runas_Spec, in which case the user may select any combination of
users and groups via the -u and -g options. In this example:

alan ALL = (root, bin : operator, system) ALL

user alan 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.

Tag_Spec
A command may have zero or more tags associated with it. There are ten possible tag values: NOPASSWD, PASSWD,
NOEXEC, EXEC, SETENV, NOSETENV, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT and NOLOG_OUTPUT. Once a tag is set on a
Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (in
other words, PASSWD overrides NOPASSWD and NOEXEC overrides EXEC).

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 fol‐
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, 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
NOSETENV tag.

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 section below.

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 section below.

Wildcards
sudo 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) and fnmatch(3) routines.
Note that these are not regular expressions.

* 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. How‐
ever, because the ‘:’ character has special meaning in sudoers, it must be escaped. For example:
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 sudo‐
ers 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.

sudoedit 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
#include and #includedir directives.

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:

#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.

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:

#include sudoers.local

the file that will be included is /etc/sudoers.local.

The file name may also include the %h escape, signifying the short form of the host name. In other words, if
the machine's host name is “xerxes”, then

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 #include, visudo will not edit the files in a #includedir 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 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 in a list or alias as well as in front of a
Cmnd. 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:

ALL,!root

If the ALL, is omitted, as in:

!root

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 below).

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): ‘!’, ‘=’, ‘:’, ‘,’, ‘(’, ‘)’, ‘\’.

SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained earlier. A list of all supported Defaults
parameters, grouped by type, are listed below.

Boolean Flags:

always_set_home If enabled, 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. Note that HOME is already set when the the env_reset option is enabled, so
always_set_home is only effective for configurations where either env_reset is disabled or
HOME is present in the env_keep list. This flag is off by default.

authenticate If set, users must authenticate themselves via a password (or other means of authentication)

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 run the command in a minimal environment containing the TERM, PATH, HOME,
MAIL, SHELL, LOGNAME, USER, USERNAME and SUDO_* variables. Any variables in the caller's
environment that match the env_keep and env_check lists are then added, followed by any vari‐
ables present in the file specified by the env_file option (if any). 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.

fast_glob Normally, sudo uses the glob(3) function to do shell-style globbing when matching path names.
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 (auto mounted). 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 path names such as ./ls or ../bin/ls. This has security implica‐
tions when path names that include globbing characters are used with the negation operator,
‘!’, as such rules can be trivially bypassed. As such, this option should not be used when
sudoers contains rules that contain negated path names which include globbing characters.
This flag is off by default.

fqdn Set this flag if you want to put fully qualified host names in the sudoers file when the local
host name (as returned by the hostname command) does not contain the domain name. In other
words, instead of myhost you would use myhost.mydomain.edu. You may still use the short form
if you wish (and even mix the two). This option is only effective when the “canonical” host
name, as returned by the getaddrinfo() or gethostbyname() function, is a fully-qualified
domain name. This is usually the case when the system is configured to use DNS for host name
resolution.

If the system is configured to use the /etc/hosts file in preference to DNS, the “canonical”
host name may not be fully-qualified. The order that sources are queried for hosts name reso‐
lution is usually specified in the /etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or,
in some cases, /etc/resolv.conf file. In the /etc/hosts file, the first host name of the
entry is considered to be the “canonical” name; subsequent names are aliases that are not used
by sudoers. For example, the following hosts file line for the machine “xyzzy” has the fully-
qualified domain name as the “canonical” host name, and the short version as an alias.

192.168.1.1 xyzzy.sudo.ws xyzzy

If the machine's hosts file entry is not formatted properly, the fqdn option will not be
effective if it is queried before DNS.

Beware that when using DNS for host name resolution, turning on fqdn requires sudoers to make
DNS lookups which renders sudo unusable if DNS stops working (for example if the machine is
disconnected from the network). Also note that just like with the hosts file, you must use
the “canonical” 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.

This flag is off by default.

ignore_dot If set, sudo will ignore "." or "" (both denoting current directory) in the PATH environment
variable; the PATH itself is not modified. This flag is on by default.

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

log_input If set, sudo will run the command in a pseudo tty and log all user input. If the standard
input is not connected to the user's tty, due to I/O redirection or because the command is
part of a pipeline, that input is also captured and stored in a separate log file.

Input is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by
default) using a unique session ID that is included in the normal sudo log line, prefixed with
“TSID=”. The iolog_file option may be used to control the format of the session ID.

Note that user input may contain sensitive information such as passwords (even if they are not
echoed to the screen), which will be stored in the log file unencrypted. In most cases, log‐
ging the command output via log_output is all that is required.

log_output If set, sudo will run the command in a pseudo tty and log all output that is sent to the
screen, similar to the script(1) command. If the standard output or standard error is not
connected to the user's tty, due to I/O redirection or because the command is part of a pipe‐
line, that output is also captured and stored in separate log files.

Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by
default) using a unique session ID that is included in the normal sudo log line, prefixed with
“TSID=”. The iolog_file option may be used to control the format of the session ID.

Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or
search the available logs.

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 (OTP) 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. If
the command the user is attempting to run is not permitted by sudoers and one of the
mail_always, mail_no_host, mail_no_perms or mail_no_user flags are set, this flag will have no
effect. 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 over‐
ridden 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.

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 feed‐
back 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 from running sudoedit. Disabling root_sudo pro‐
vides 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 enabled 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. Note that HOME is already set when the the
env_reset option is enabled, so set_home is only effective for configurations where either
env_reset is disabled or HOME is present in the env_keep list. 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_log‐
name 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 on by default.

set_utmp When enabled, sudo will create an entry in the utmp (or utmpx) file when a pseudo-tty is allo‐
cated. A pseudo-tty is allocated by sudo when the log_input, log_output or use_pty flags are
enabled. By default, the new entry will be a copy of the user's existing utmp entry (if any),
with the tty, time, type and pid fields updated. This flag is on by default.

setenv Allow the user to disable the env_reset option from the command line via the -E option. Addi‐
tionally, 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).
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. With this flag enabled, sudo will use a
file named for the tty the user is logged in on in the user's time stamp directory. If dis‐
abled, the time stamp of the directory is used instead. 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.

use_pty If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone. A
malicious program run under sudo could conceivably fork a background process that retains to
the user's terminal device after the main program has finished executing. Use of this option
will make that impossible. This flag is off by default.

utmp_runas If set, sudo will store the name of the runas user when updating the utmp (or utmpx) file. By
default, sudo stores the name of the invoking user. 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 pass‐
word even when it would be visible on the screen. This makes it possible to run things like
“ssh somehost sudo ls” since by default, ssh(1) does not allocate a tty when running a com‐
mand. 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, or 0 for no timeout. The timeout
may include a fractional component if minute granularity is insufficient, for example 2.5.
The default is 5.

timestamp_timeout
Number of minutes that can elapse before sudo will ask for a passwd again. The timeout may
include a fractional component if minute granularity is insufficient, for example 2.5. 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 time stamp will never expire. This can be used to allow users to create or delete
their own time stamps 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 the

iolog_dir The top-level directory to use when constructing the path name for the input/output log direc‐
tory. Only used if the log_input or log_output options are enabled or when the LOG_INPUT or
LOG_OUTPUT tags are present for a command. The session sequence number, if any, is stored in
the directory. The default is /var/log/sudo-io.

The following percent (‘%’) escape sequences are supported:

%{seq}
expanded to a monotonically increasing base-36 sequence number, such as 0100A5, where
every two digits are used to form a new directory, e.g. 01/00/A5

%{user}
expanded to the invoking user's login name

%{group}
expanded to the name of the invoking user's real group ID

%{runas_user}
expanded to the login name of the user the command will be run as (e.g. root)

%{runas_group}
expanded to the group name of the user the command will be run as (e.g. wheel)

%{hostname}
expanded to the local host name without the domain name

%{command}
expanded to the base name of the command being run

In addition, any escape sequences supported by the system's strftime(3) function will be
expanded.

To include a literal ‘%’ character, the string ‘%%’ should be used.

iolog_file The path name, relative to iolog_dir, in which to store input/output logs when the log_input
or log_output options are enabled or when the LOG_INPUT or LOG_OUTPUT tags are present for a
command. Note that iolog_file may contain directory components. The default is “%{seq}”.

See the iolog_dir option above for a list of supported percent (‘%’) escape sequences.

In addition to the escape sequences, path names that end in six or more Xs will have the Xs
replaced with a unique combination of digits and letters, similar to the mktemp(3) function.

mailsub Subject of the mail sent to the mailto user. The escape %h will expand to the host name of
the machine. Default is “*** SECURITY information for %h ***”.

noexec_file This option is no longer supported. The path to the noexec file should now be set in the
/etc/sudo.conf file.

pam_login_service
On systems that use PAM for authentication, this is the service name used when the -i option
is specified. The default value is “sudo-i”. See the description of pam_service for more
information.
%h expanded to the local host name 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 when 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.

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

The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice,
and warning.

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

See syslog_badpri for the list of supported syslog priorities.

sudoers_locale Locale to use when parsing the sudoers file, logging commands, and sending email. Note that
changing the locale may affect how sudoers is interpreted. Defaults to “C”.

timestampdir The directory in which sudo stores its time stamp files. The default is /var/db/sudo.

timestampowner The owner of the time stamp directory and the time stamps 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 when sudo is built with SELinux support.

Strings that can be used in a boolean context:

env_file The env_file option 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 either be of the form
“VARIABLE=value” or “export VARIABLE=value”. The value may optionally be surrounded by single or
double quotes. 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. The group name specified
should not include a % prefix. This is not set by default.

group_plugin A string containing a sudoers group plugin with optional arguments. This can be used to implement
support for the nonunix_group syntax described earlier. The string should consist of the plugin

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 config‐
ure 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 option is not set by default.

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

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 unless they are considered
“safe”. For all variables except TZ, “safe” means that the variable's value does not contain
any ‘%’ or ‘/’ characters. This can be used to guard against printf-style format vulnerabili‐
ties in poorly-written programs. The TZ variable is considerd unsafe if any of the following
are true:

· It consists of a fully-qualified path name, optionally prefixed with a colon (‘:’), that
does not match the location of the zoneinfo directory.

· It contains a .. path element.

· It contains white space or non-printable characters.

· It is longer than the value of PATH_MAX.

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 dis‐
abled, 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 when the env_reset option is
not in effect. 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.

LOG FORMAT
sudoers can log events using either syslog(3) or a simple log file. In each case the log format is almost iden‐
tical.

Accepted command log entries
Commands that sudo runs are logged using the following format (split into multiple lines for readability):

date hostname progname: username : TTY=ttyname ; PWD=cwd ; \

syslog(3).

username The login name of the user who ran sudo.

ttyname The short name of the terminal (e.g. “console”, “tty01”, or “pts/0”) sudo was run on, or “unknown”
if there was no terminal present.

cwd The current working directory that sudo was run in.

runasuser The user the command was run as.

runasgroup The group the command was run as if one was specified on the command line.

logid An I/O log identifier that can be used to replay the command's output. This is only present when
the log_input or log_output option is enabled.

env_vars A list of environment variables specified on the command line, if specified.

command The actual command that was executed.

Messages are logged using the locale specified by sudoers_locale, which defaults to the “C” locale.

Denied command log entries
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible
reasons include:

user NOT in sudoers
The user is not listed in the sudoers file.

user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run commands on the host.

command not allowed
The user is listed in the sudoers file for the host but they are not allowed to run the specified command.

3 incorrect password attempts
The user failed to enter their password after 3 tries. The actual number of tries will vary based on the num‐
ber of failed attempts and the value of the passwd_tries option.

a password is required
sudo's -n option was specified but a password was required.

sorry, you are not allowed to set the following environment variables
The user specified environment variables on the command line that were not allowed by sudoers.

Error log entries
If an error occurs, sudoers will log a message and, in most cases, send a message to the administrator via
email. Possible errors include:

parse error in /etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In some cases, the actual error may be one line
above or below the line number listed, depending on the type of error.

problem with defaults entries

/etc/sudo.conf file.

unable to stat /etc/sudoers
The /etc/sudoers file is missing.

/etc/sudoers is not a regular file
The /etc/sudoers file exists but is not a regular file or symbolic link.

/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the sudoers file owner, please add
“sudoers_uid=N” (where ‘N’ is the user ID that owns the sudoers file) to the sudoers plugin line in the
/etc/sudo.conf file.

/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to it. The sudoers file must not be world-
writable, the default file mode is 0440 (readable by owner and group, writable by none). The default mode may
be changed via the “sudoers_mode” option to the sudoers plugin line in the /etc/sudo.conf file.

/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to change the sudoers file group ownership,
please add “sudoers_gid=N” (where ‘N’ is the group ID that owns the sudoers file) to the sudoers plugin line
in the /etc/sudo.conf file.

unable to open /var/db/sudo/username/ttyname
sudoers was unable to read or create the user's time stamp file.

unable to write to /var/db/sudo/username/ttyname
sudoers was unable to write to the user's time stamp file.

unable to mkdir to /var/db/sudo/username
sudoers was unable to create the user's time stamp directory.

Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by the sys‐
log daemon, not sudoers itself. As such, they may vary in format on different systems.

On most systems, syslog(3) has a relatively small log buffer. To prevent the command line arguments from being
truncated, sudoers will split up log messages that are larger than 960 characters (not including the date, host‐
name, and the string “sudo”). When a message is split, additional parts will include the string “(command
continued)” after the user name and before the continued command line arguments.

Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a file,
sudoers uses a format similar to syslog(3), with a few important differences:

1. The progname and hostname fields are not present.

2. If the log_year option is enabled, the date will also include the year.

3. Lines that are longer than loglinelen characters (80 by default) are word-wrapped and continued on the next
line with a four character indent. This makes entries easier to read for a human being, but makes it more
difficult to use grep(1) on the log files. If the loglinelen option is set to 0 (or negated with a ‘!’),
word wrap will be disabled.

# Debug sudo /var/log/sudo_debug all@warn
# Set disable_coredump true
#
# The plugin_path is relative to /usr/libexec unless
# fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
# that contains the plugin interface structure.
# The plugin_options are optional.
#
Plugin policy_plugin sudoers.so
Plugin io_plugin sudoers.so

Plugin options
Starting with sudo 1.8.5, it is possible to pass options to the sudoers plugin. Options may be listed after the
path to the plugin (i.e. after sudoers.so); multiple options should be space-separated. For example:

Plugin sudoers_policy sudoers.so sudoers_file=/etc/sudoers sudoers_uid=0 sudoers_gid=0 sudoers_mode=0440

The following plugin options are supported:

sudoers_file=pathname
The sudoers_file option can be used to override the default path to the sudoers file.

sudoers_uid=uid
The sudoers_uid option can be used to override the default owner of the sudoers file. It should be
specified as a numeric user ID.

sudoers_gid=gid
The sudoers_gid option can be used to override the default group of the sudoers file. It should be
specified as a numeric group ID.

sudoers_mode=mode
The sudoers_mode option can be used to override the default file mode for the sudoers file. It should
be specified as an octal value.

Debug flags
Versions 1.8.4 and higher of the sudoers plugin supports a debugging framework that can help track down what the
plugin is doing internally if there is a problem. This can be configured in the /etc/sudo.conf file as
described in sudo(8).

The sudoers plugin uses the same debug flag format as the sudo front-end: subsystem@priority.

The priorities used by sudoers, in order of decreasing severity, are: crit, err, warn, notice, diag, info, trace
and debug. Each priority, when specified, also includes all priorities higher than it. For example, a priority
of notice would include debug messages logged at notice and higher.

The following subsystems are used by sudoers:

alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing

all matches every subsystem

audit BSM and Linux audit code

netif network interface handling

nss network service switch handling in sudoers

parser sudoers file parsing

perms permission setting

plugin The equivalent of main for the plugin.

pty pseudo-tty related code

rbtree redblack tree internals

util utility functions

FILES
/etc/sudo.conf Sudo front end configuration

/etc/sudoers List of who can run what

/etc/group Local groups file

/etc/netgroup List of network groups

/var/log/sudo-io I/O log files

/var/db/sudo Directory containing time stamps for the sudoers security policy

/etc/environment Initial environment for -i mode on AIX and Linux systems

EXAMPLES
Below are example sudoers entries. Admittedly, some of these are a bit contrived. First, we allow a few envi‐
ronment 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 :\

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 them‐
selves.

PARTTIMERS ALL = ALL

Part time sysadmins bostley, jwfox, and crawl) may run any command on any host but they must authenticate them‐
selves 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 nota‐
tion) 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).

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

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 Runas_Alias
(the adm and oper groups).

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 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.

SECURITY NOTES
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL using the ‘!’ operator. A user can trivially cir‐
cumvent 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 or SHELLS since he can simply copy those com‐
mands 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 specifica‐
tion.

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 secu‐
rity issue for rules that subtract or revoke privileges.

For example, given the following sudoers entry:

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

User john can still run /usr/bin/passwd root if fast_glob is enabled by changing to /usr/bin and running
./passwd root instead.

Preventing shell escapes
Once sudo executes a program, that program is free to do whatever it pleases, including run other programs.
This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user
bypass 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:

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 run‐
ning 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.

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 sys‐
tems, 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.

To enable noexec for a command, use the NOEXEC tag as documented in the User Specification section

Time stamp file checks
sudoers will check the ownership of its time stamp directory (/var/db/sudo by default) and ignore the direc‐
tory's contents if it is not owned by root or if it is writable by a user other than root. On systems that
allow non-root users to give away files via chown(2), if the time stamp directory is located in a world-writable
directory (e.g., /tmp), it is possible for a user to create the time stamp directory before sudo is run. How‐
ever, because sudoers checks the ownership and mode of the directory and its contents, the only damage that can
be done is to “hide” files by putting them in the time stamp dir. This is unlikely to happen since once the
time stamp dir is owned by root and inaccessible by any other user, the user placing files there would be unable
to get them back out.

sudoers will not honor time stamps set far in the future. Time stamps with a date greater than current_time + 2
* TIMEOUT will be ignored and sudo will log and complain. This is done to keep a user from creating his/her own
time stamp with a bogus date on systems that allow users to give away files if the time stamp directory is
located in a world-writable directory.

On systems where the boot time is available, sudoers will ignore time stamps that date from before the machine
booted.

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 time stamp file's modification time is within 5 minutes (or whatever the timeout
is set to in sudoers). When the tty_tickets option is enabled, the time stamp has per-tty granularity but still
may outlive the user's session. On Linux systems where the devpts filesystem is used, Solaris systems with the
devices filesystem, as well as other systems that utilize a devfs filesystem that monotonically increase the
inode number of devices as they are created (such as Mac OS X), sudoers is able to determine when a tty-based
time stamp file is stale and will ignore it. Administrators should not rely on this feature as it is not uni‐
versally available.

SEE ALSO
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudoers.ldap(5), sudo_plugin(8), sudo(8), visudo(8)

CAVEATS
The sudoers file should always be edited by the visudo command which locks the file and does grammatical check‐
ing. It is imperative that sudoers be free of syntax errors since sudo will not run with a syntactically incor‐
rect sudoers file.

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

BUGS
If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/

SUPPORT
Limited free support is available via the sudo-users mailing list, see http://www.sudo.ws/mailman/listinfo/sudo-
users to subscribe or search the archives.

DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the implied war‐
ranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distrib‐
uted with sudo or http://www.sudo.ws/sudo/license.html for complete details.

Sudo 1.8.6p7 July 16, 2012 Sudo 1.8.6p7