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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 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 pol‐
icy information in LDAP, please see sudoers.ldap(5).

Authentication and logging
The sudoers security policy requires that most users authenticate them‐
selves 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 com‐
mand. Unlike su(1), when sudoers requires authentication, it validates
the invoking user's credentials, not the target user's (or root's) cre‐
dentials. 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 authorities. 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 pro‐
vides 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. The new environment contains the TERM, PATH,
HOME, MAIL, SHELL, LOGNAME, USER, USERNAME and SUDO_* variables in addi‐
tion 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 explic‐
itly 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 dan‐
gerous 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 out‐
put of “sudo -V” when run as root.

Note that the dynamic linker on most operating systems will remove vari‐
ables that can control dynamic linking from the environment of setuid
executables, including sudo. Depending on the operating system this may
include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, 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's -i option (initial login) is specified,
sudoers will initialize the environment regardless of the value of
env_reset. The DISPLAY, PATH and TERM variables remain unchanged; HOME,
MAIL, SHELL, USER, and LOGNAME are set based on the target user. On AIX
(and Linux systems without PAM), the contents of /etc/environment are
also included. 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 con‐
flict 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 neces‐
sarily the most specific match).

The sudoers grammar will be described below in Extended Backus-Naur Form
(EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly sim‐
ple, 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, con‐
fuse 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

Alias_Type NAME = item1, item2, ...

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

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

The definitions of what constitutes a valid alias member follow.

User_List ::= User |
User ',' User_List

A User_List is made up of one or more user names, user ids (prefixed with
‘#’), system group names and ids (prefixed with ‘%’ and ‘%#’ respec‐
tively), 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 ‘!’ operators. 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 char‐
acters. Alternately, special characters may be specified in escaped hex
mode, e.g. \x20 for space. When using double quotes, any prefix charac‐
ters 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 Name@FULLY.QUALIFIED.DOMAIN"

· Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"

Note that quotes around group names are optional. Unquoted strings must
use a backslash (‘\’) to escape spaces and special characters. See Other
special characters and reserved words for a list of characters that need
to be escaped.

Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List

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)? |
'!'* +netgroup |
'!'* Host_Alias

A Host_List 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 corre‐
sponds to one of the hosts's network interfaces, the corresponding net‐
mask 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 host
name command on your machine returns the fully qualified host name,
you'll need to use the fqdn option for wildcards to be useful. Note that
sudo only inspects actual network interfaces; this means that IP address
127.0.0.1 (localhost) will never match. Also, the host name “localhost”
will only match if that is the actual host name, which is usually only
the case for non-networked systems.

Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List

command name ::= file name |
file name args |
file name '""'

Cmnd ::= '!'* command name |
'!'* directory |
'!'* "sudoedit" |
'!'* 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 sim‐
ple 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 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 char‐
acters 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 com‐
mand line arguments just as a normal command does.

Defaults
Certain configuration options may be changed from their default values at
run-time via one or more Default_Entry 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 Cmnd_Alias 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 |
'!'* 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 back‐
slash (‘\’).

Lists have two additional assignment operators, += and -=. These opera‐
tors 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 paren‐
theses. The first Runas_List indicates which users the command may be
run as via sudo's -u option. The second defines a list of groups that
can be specified via sudo's -g option. If both Runas_Lists are speci‐
fied, the command may be run with any combination of users and groups
listed in their respective Runas_Lists. 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 Runas_List 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 Runas_List. If both Runas_Lists are empty, the command may
only be run as the invoking user. If no Runas_Spec is specified the com‐
mand may be run as root and no group may be specified.

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

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

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

$ sudo -u operator /bin/ls

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

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

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

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

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

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 set‐
ting 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
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 pass‐
word 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 operat‐
ing system supports it, the NOEXEC tag can be used to prevent a dynami‐
cally-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 dis‐
able the env_reset option from the command line via the -E option. Addi‐
tionally, 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 man‐
ner. 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. However, because the ‘:’ character
has special meaning in sudoers, it must be escaped. For example:

/bin/ls [[alpha]]*

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:

/usr/bin/*

match /usr/bin/who 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.

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 direc‐
tives.

This can be used, for example, to keep a site-wide sudoers file in addi‐
tion 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

#include /etc/sudoers.%h

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

The #includedir directive can be used to create a sudo.d directory that
the system package manager can drop sudoers rules into as part of package
installation. For example, given:

#includedir /etc/sudoers.d

sudo 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 #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 prefer‐
ence 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 char‐
acters 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 ear‐
lier. 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 con‐
figurations 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 pass‐
word (or other means of authentication) before they may
run commands. This default may be overridden via the
PASSWD and NOPASSWD tags. This flag is on by default.

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

compress_io If set, and sudo is configured to log a command's input
or output, the I/O logs will be compressed using zlib.
This flag is on by default when sudo is compiled with
zlib support.

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

env_reset If set, sudo will run the command in a minimal environ‐
ment 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 variables 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 match‐
ing. The disadvantage of fast_glob is that it is
unable to match relative path names such as ./ls or
../bin/ls. This has security implications when path
names that include globbing characters are used with
the negation operator, ‘!’, as such rules can be triv‐
ially 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 con‐
figured 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 resolution 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 net‐
work). 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 cur‐
rent directory) in the PATH environment variable; the
PATH itself is not modified. This flag is on by
default.

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

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

log_host If set, the host name will be logged in the (non-sys‐
log) 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 con‐
nected 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 unen‐
crypted. In most cases, logging 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 stan‐
dard error is not connected to the user's tty, due to
I/O redirection or because the command is part of a
pipeline, 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) util‐
ity, 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 overridden by a EXEC
tag. See the description of NOEXEC and EXEC below as
well as the Preventing shell escapes section at the end
of this manual. This flag is off by default.

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

passprompt_override
The password prompt specified by passprompt will nor‐
mally only be used if the password prompt provided by
systems such as PAM matches the string “Password:”. If
passprompt_override is set, passprompt will always be
used. This flag is off by default.

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

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

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

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

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

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

set_home If 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_logname option.
Note that if the env_reset option has not been dis‐
abled, 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 allocated. 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. Additionally, environ‐
ment variables set via the command line are not subject
to the restrictions imposed by env_check, env_delete,
or env_keep. As such, only trusted users should be
allowed to set variables in this manner. This flag is
off by default.

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

stay_setuid Normally, when sudo executes a command the real and
effective UIDs are set to the target user (root by
default). This option changes that behavior such that
the real UID is left as the invoking user's UID. In
other words, this makes sudo act as a setuid wrapper.
This can be useful on systems that disable some poten‐
tially dangerous functionality when a program is run
setuid. This option is only effective on systems that
support either the setreuid(2) or setresuid(2) system
call. This flag is off by default.

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

tty_tickets If set, users must authenticate on a per-tty basis.
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 disabled, 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 spec‐
ify 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. 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 password even when it would be visi‐
ble 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 command.
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 pass‐
word 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 insuffi‐
cient, 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 frac‐
tional 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” respec‐
tively.

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 value of the umask option, which
defaults to 0022. This guarantees that sudo never low‐
ers the umask when running a command. Note: on systems
that use PAM, the default PAM configuration may specify
its own umask which will override the value set in
sudoers.

Strings:

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

editor A colon (‘:’) separated list of editors allowed to be
used with visudo. visudo will choose the editor that
matches the user's EDITOR environment variable if pos‐
sible, or the first editor in the list that exists and
is executable. The default is /usr/local/bin/vi.

iolog_dir The top-level directory to use when constructing the
path name for the input/output log directory. 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 sup‐
ported:

%{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 com‐
mand will be run as (e.g. root)

%{runas_group}
expanded to the group name of the user the com‐
mand 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 sys‐
tem'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.

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

%H expanded to the local host name including the
domain name (only if the machine's host name is
fully qualified or the fqdn option is set)

%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 com‐
mand 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:”. 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 avail‐
able 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 unsuc‐
cessfully. 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 success‐
fully. Defaults to notice.

See syslog_badpri for the list of supported syslog pri‐
orities.

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 avail‐
able 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 path, either fully-qualified or rela‐
tive to the /usr/libexec directory, followed by any config‐
uration arguments the plugin requires. These arguments (if
any) will be passed to the plugin's initialization func‐
tion. If arguments are present, the string must be
enclosed in double quotes ("").

For example, given /etc/sudo-group, a group file in Unix
group format, the sample group plugin can be used:

Defaults group_plugin="sample_group.so /etc/sudo-group"

For more information see sudo_plugin(5).

lecture This option controls when a short lecture will be printed
along with the password prompt. It has the following pos‐
sible 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). Set‐
ting a path turns on logging to a file; negating this
option turns it off. By default, sudo logs via syslog.

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

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

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

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

secure_path Path used for every command run from sudo. If you don't
trust the people running sudo to have a sane PATH environ‐
ment 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.

The following syslog facilities are supported: authpriv (if
your OS supports it), auth, daemon, user, local0, local1,
local2, local3, local4, local5, local6, and local7.

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

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

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

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

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

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

Lists that can be used in a boolean context:

env_check Environment variables to be removed from the user's
environment if the variable's value contains ‘%’ or ‘/’
characters. This can be used to guard against printf-
style format vulnerabilities in poorly-written pro‐
grams. The argument may be a double-quoted, space-sep‐
arated list or a single value without double-quotes.
The list can be replaced, added to, deleted from, or
disabled by using the =, +=, -=, and ! operators
respectively. Regardless of whether the env_reset
option is enabled or disabled, variables specified by
env_check will be preserved in the environment if they
pass the aforementioned check. The default list of
environment variables to check is displayed when sudo
is run by root with the -V option.

env_delete Environment variables to be removed from the user's
environment 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 dis‐
played when sudo is run by root with the -V option.
Note that many operating systems will remove poten‐
tially 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 identical.

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 ; \
USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command

Where the fields are as follows:

date The date the command was run. Typically, this is in the
format “MMM, DD, HH:MM:SS”. If logging via syslog(3), the
actual date format is controlled by the syslog daemon. If
logging to a file and the log_year option is enabled, the
date will also include the year.

hostname The name of the host sudo was run on. This field is only
present when logging via syslog(3).

progname The name of the program, usually sudo or sudoedit. This
field is only present when logging via 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 ter‐
minal 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 com‐
mand'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 com‐
mands 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 num‐
ber of tries will vary based on the number 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
The sudoers file contains one or more unknown Defaults settings. This
does not prevent sudo from running, but the sudoers file should be
checked using visudo.

timestamp owner (username): No such user
The time stamp directory owner, as specified by the timestampowner set‐
ting, could not be found in the password database.

unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can happen when
the sudoers file is located on a remote file system that maps user ID 0
to a different value. Normally, sudoers tries to open sudoers using
group permissions to avoid this problem. Consider changing the owner‐
ship of /etc/sudoers by adding an option like “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.

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 syslog 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,
hostname, 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.

SUDO.CONF
The /etc/sudo.conf file determines which plugins the sudo front end will
load. If no /etc/sudo.conf file is present, or it contains no Plugin
lines, sudo will use the sudoers security policy and I/O logging, which
corresponds to the following /etc/sudo.conf file.

#
# Default /etc/sudo.conf file
#
# Format:
# Plugin plugin_name plugin_path plugin_options ...
# Path askpass /path/to/askpass
# Path noexec /path/to/sudo_noexec.so
# 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 exam‐
ple, 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

auth user authentication

defaults sudoers Defaults settings

env environment handling

ldap LDAP-based sudoers

logging logging support

match matching of users, groups, hosts and netgroups in sudoers

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 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 = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules

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

Here we override some of the compiled in default values. We want sudo to
log via syslog(3) using the auth facility in all cases. We don't want to
subject the full time staff to the sudo lecture, user millert need not
give a password, and we don't want to reset the LOGNAME, USER or USERNAME
environment variables when running commands as root. Additionally, on
the machines in the SERVERS Host_Alias, we keep an additional local log
file and make sure we log the year in each log line since the log entries
will be kept around for several years. Lastly, we disable shell escapes
for the commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and
/usr/bin/less).

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

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

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

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

FULLTIMERS ALL = NOPASSWD: ALL

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

PARTTIMERS ALL = ALL

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

jack CSNETS = ALL

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

lisa CUNETS = ALL

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

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

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

joe ALL = /usr/bin/su operator

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

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

%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 multi‐
ple 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_com‐
mands/ but only as user operator.

matt valkyrie = KILL

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

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

On the host www, any user in the WEBMASTERS User_Alias (will, wendy, and
wim), may run any command as user www (which owns the web pages) or sim‐
ply su(1) to www.

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

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

SECURITY NOTES
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 exam‐
ple:

bill ALL = ALL, !SU, !SHELLS

Doesn't really prevent bill from running the commands listed in SU or
SHELLS since he can simply copy those commands to a different name, or
use a shell escape from an editor or other program. Therefore, these
kind of restrictions should be considered advisory at best (and rein‐
forced 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 specifi‐
cation.

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 rela‐
tive paths. While this is typically only an inconvenience for rules that
grant privileges, it can result in a security issue for rules that sub‐
tract 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 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.

noexec Many systems that support shared libraries have the ability to
override default library functions by pointing an environment
variable (usually LD_PRELOAD) to an alternate shared library.
On such systems, sudo's noexec functionality can be used to
prevent a program run by sudo from executing any other pro‐
grams. Note, however, that this applies only to native dynami‐
cally-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 oper‐
ating 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 docu‐
mented 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.

Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/var/db/sudo 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. 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. However, 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 monotoni‐
cally 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 fea‐
ture as it is not universally 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 checking. It is imperative that
sudoers be free of syntax errors since sudo will not run with a syntacti‐
cally incorrect 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, includ‐
ing, but not limited to, the implied warranties of merchantability and
fitness for a particular purpose are disclaimed. See the LICENSE file
distributed with sudo or http://www.sudo.ws/sudo/license.html for com‐
plete details.

Sudo 1.8.6p7 July 16, 2012 Sudo 1.8.6p7

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