Ubuntu Manpage: sudoers — default sudo security policy plugin

Provided by: sudo-ldap_1.8.21p2-3ubuntu1.6_amd64

NAME

     sudoers — default sudo security policy plugin

DESCRIPTION

The sudoers policy plugin determines a user's sudo privileges. It is the default sudo policy plugin. The
policy is driven by the /etc/sudoers file or, optionally in LDAP. The policy format is described in detail
in the SUDOERS FILE FORMAT section. For information on storing sudoers policy information in LDAP, please
see sudoers.ldap(5).

Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which policy and and I/O logging plugins to load. If no
sudo.conf(5) file is present, or if it contains no Plugin lines, sudoers will be used for policy decisions
and I/O logging. To explicitly configure sudo.conf(5) to use the sudoers plugin, the following
configuration can be used.

Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so

Starting with sudo 1.8.5, it is possible to specify optional arguments to the sudoers plugin in the
sudo.conf(5) file. These arguments, if present, should be listed after the path to the plugin (i.e. after
sudoers.so). Multiple arguments may be specified, separated by white space. For example:

Plugin sudoers_policy sudoers.so sudoers_mode=0400

The following plugin arguments are supported:

ldap_conf=pathname
The ldap_conf argument can be used to override the default path to the ldap.conf file.

ldap_secret=pathname
The ldap_secret argument can be used to override the default path to the ldap.secret file.

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

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

sudoers_gid=gid
The sudoers_gid argument can be used to override the default group of the sudoers file. It must
be specified as a numeric group ID (not a group name).

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

For more information on configuring sudo.conf(5), please refer to its manual.

User Authentication
The sudoers security policy requires that most users authenticate themselves before they can use sudo. A
password is not required if the invoking user is root, if the target user is the same as the invoking user,
or if the policy has disabled authentication for the user or command. Unlike su(1), when sudoers requires
authentication, it validates the invoking user's credentials, not the target user's (or root's)
credentials. This can be changed via the rootpw, 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 no mail will be sent if an unauthorized user tries to run sudo with the -l or -v option unless
there is an authentication error and either the mail_always or mail_badpass flags are enabled. This allows
users to determine for themselves whether or not they are allowed to use sudo. All attempts to run sudo
(successful or not) will be logged, regardless of whether or not mail is sent.

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 file lookup is still done for root, not the
user specified by SUDO_USER.

sudoers uses per-user time stamp files for credential caching. Once a user has been authenticated, a
record is written containing the user ID that was used to authenticate, the terminal session ID, and a time
stamp (using a monotonic clock if one is available). The user may then use sudo without a password for a
short period of time (15 minutes unless overridden by the timestamp_timeout option). By default, sudoers
uses a separate record for each terminal, which means that a user's login sessions are authenticated
separately. The timestamp_type option can be used to select the type of time stamp record sudoers will
use.

Logging
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. See LOG FORMAT for a description of the log file format.

sudoers is also capable of running a command in a pseudo-tty and logging all input and/or output. The
standard input, standard output and standard error can be logged even when not associated with a terminal.
I/O logging is not on by default but can be enabled using the log_input and log_output options as well as
the LOG_INPUT and LOG_OUTPUT command tags. See I/O LOG FILES for details on how I/O log files are stored.

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
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 addition to variables from the invoking process permitted by the env_check
and env_keep options. This is effectively a whitelist for environment variables. Environment variables
with a value beginning with () are removed unless both the name and value parts are matched by env_keep or
env_check, as they may be interpreted as functions by the bash shell. Prior to version 1.8.11, such
variables were always removed.

If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and
env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave
like a blacklist. Prior to version 1.8.21, environment variables with a value beginning with () were
always removed. Beginning with version 1.8.21, a pattern in env_delete is used to match bash shell
functions instead. Since it is not possible to blacklist all potentially dangerous environment variables,
use of the default env_reset behavior is encouraged.

Environment variables specified by env_check, env_delete, or env_keep may include one or more ‘*’
characters which will match zero or more characters. No other wildcard characters are supported.

By default, environment variables are matched by name. However, if the pattern includes an equal sign
(‘=’), both the variables name and value must match. For example, a bash shell function could be matched
as follows:

env_keep += "BASH_FUNC_my_func%%=()*"

Without the “=()*” suffix, this would not match, as bash shell functions are not preserved by default.

The complete list of environment variables that sudo allows or denies is contained in the output of “sudo
-V” when run as root. Please note that this list varies based on the operating system sudo is running on.

On systems that support PAM where the pam_env module is enabled for sudo, variables in the PAM environment
may be merged in to the environment. If a variable in the PAM environment is already present in the user's
environment, the value will only be overridden if the variable was not preserved by sudoers. When
env_reset is enabled, variables preserved from the invoking user's environment by the env_keep list take
precedence over those in the PAM environment. When env_reset is disabled, variables present the invoking
user's environment take precedence over those in the PAM environment unless they match a pattern in the
env_delete list.

Note that the dynamic linker on most operating systems will remove variables that can control dynamic
linking from the environment of setuid executables, including sudo. Depending on the operating system this
may include _RLD*, 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, the restricted_env_file and env_file files are applied, if present. The variables in
restricted_env_file are applied first and are subject to the same restrictions as the invoking user's
environment, as detailed above. The variables in env_file are applied last and are not subject to these
restrictions. In both cases, variables present in the files will only be set to their specified values if
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 file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you
are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.

Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up
of production rules. 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

Alias_Type NAME = item1, item2, ...

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

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

It is a syntax error to redefine an existing alias. It is possible to use the same name for aliases of
different types, but this is not recommended.

The definitions of what constitutes a valid alias 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 ‘%#’ 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 ‘!’ operators. An odd number of ‘!’ operators negate the value of the item; an even number just
cancel each other out. User netgroups are matched using the user and domain members only; the host member
is not used when matching.

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. For
instance, the QAS AD plugin supports the following formats:

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

• Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"

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

See GROUP PROVIDER PLUGINS for more information.

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

Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List

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. Host netgroups
are matched using the host (both qualified and unqualified) and domain members only; the user member is not
used when matching. If you specify a network number without a netmask, sudo will query each of the local
host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces,
will use the netmask of that interface. 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.

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 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
characters must be escaped with a ‘\’ if they are used in command arguments: ‘,’, ‘:’, ‘=’, ‘\’. The
built-in 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. Note that “sudoedit” is a command built
into sudo itself and must be specified in the sudoers file without a leading path.

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==

Warning, if the user has write access to the command itself (directly or via a sudo command), it may be
possible for the user to replace the command after the digest check has been performed but before the
command is executed. A similar race condition exists on systems that lack the fexecve(2) system call when
the directory in which the command is located is writable by the user. See the description of the fdexec
setting for more information on how sudo executes commands that have an associated digest.

Command digests are only supported by version 1.8.7 or higher.

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 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, user and runas Defaults first, then
command defaults. If there are multiple Defaults settings of the same type, the last matching setting is
used. The following Defaults settings are parsed before all others since they may affect subsequent
entries: fqdn, group_plugin, runas_default, sudoers_locale.

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? Option_Spec* Tag_Spec* Cmnd

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

Option_Spec ::= (SELinux_Spec | Date_Spec | Timeout_Spec)

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

Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')

Timeout_Spec ::= 'TIMEOUT=timeout'

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 list of groups that can be specified via sudo's -g option. If both Runas_Lists are
specified, 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 command 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 on the host boulder—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 setting the group to operator or
system.

Option_Spec
A Cmnd may have zero or more options associated with it. Depending on the system, options may consist of
SELinux roles and/or types, Solaris privileges sets, and command timeouts. Once an option is set for a
Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit that option unless it is overridden by another
option.

SELinux_Spec
On systems with SELinux support, sudoers file 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.

Date_Spec
sudoers rules can be specified with a start and end date via the NOTBEFORE and NOTAFTER settings. The time
stamp must be specified in Generalized Time as defined by RFC 4517. The format is effectively
yyyymmddHHMMSSZ where the minutes and seconds are optional. The ‘Z’ suffix indicates that the time stamp
is in Coordinated Universal Time (UTC). It is also possible to specify a timezone offset from UTC in hours
and minutes instead of a ‘Z’. For example, ‘-0500’ would correspond to Eastern Standard time in the US.
As an extension, if no ‘Z’ or timezone offset is specified, local time will be used.

The following are all valid time stamps:

20170214083000Z
2017021408Z
20160315220000-0500
20151201235900

Timeout_Spec
A command may have a timeout associated with it. If the timeout expires before the command has exited, the
command will be terminated. The timeout may be specified in combinations of days, hours, minutes and
seconds with a single-letter case-insensitive suffix that indicates the unit of time. For example, a
timeout of 7 days, 8 hours, 30 minutes and 10 seconds would be written as 7d8h30m10s. If a number is
specified without a unit, seconds are assumed. Any of the days, minutes, hours or seconds may be omitted.
The order must be from largest to smallest unit and a unit may not be specified more than once.

The following are all valid timeout values: 7d8h30m10s, 14d, 8h30m, 600s, 3600. The following are invalid
timeout values: 12m2w1d, 30s10m4h, 1d2d3h.

This option is only supported by version 1.8.20 or higher.

Tag_Spec
A command may have zero or more tags associated with it. The following tag values are supported: EXEC,
NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, PASSWD, NOPASSWD,
SETENV, and NOSETENV. 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).

EXEC and NOEXEC

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.

FOLLOW and NOFOLLOW Starting with version 1.8.15, sudoedit will not open a file that is a symbolic link
unless the sudoedit_follow option is enabled. The FOLLOW and NOFOLLOW tags override the value of
sudoedit_follow and can be used to permit (or deny) the editing of symbolic links on a per-command basis.
These tags are only effective for the sudoedit command and are ignored for all other commands.

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.

MAIL and NOMAIL

These tags provide fine-grained control over whether mail will be sent when a user runs a command by
overriding the value of the mail_all_cmnds option on a per-command basis. They have no effect when sudo
is run with the -l or -v options. A NOMAIL tag will also override the mail_always and mail_no_perms
options. For more information, see the descriptions of mail_all_cmnds, mail_always, and mail_no_perms in
the SUDOERS OPTIONS section below.

PASSWD and NOPASSWD

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

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

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

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

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

By default, if the NOPASSWD tag is applied to any of the entries for a user on the current host, he or
she will be able to run “sudo -l” without a password. Additionally, a user may only run “sudo -v”
without a password if the NOPASSWD tag is present for all a user's entries that pertain to the current
host. This behavior may be overridden via the verifypw and listpw options.

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.

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 glob(3) and fnmatch(3)
functions as specified by IEEE Std 1003.1 (“POSIX.1”).

* Matches any set of zero or more characters (including white space).

? Matches any single character (including white space).

[...] 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 ‘]’.

Note that these are not regular expressions. Unlike a regular expression there is no way to match one or
more characters within a range.

Character classes may 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 file name portion of the
command. 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.
Command line arguments are matched as a single, concatenated string. This mean a wildcard character such
as ‘?’ or ‘*’ will match across word boundaries, which may be unexpected. 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. In most cases it is better to do command line processing outside
of the sudoers file in a scripting language.

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 file 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 file 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 sudoers.d directory that the system package manager can
drop sudoers file rules into as part of package installation. For example, given:

#includedir /etc/sudoers.d

sudo will suspend processing of the current file and 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. After parsing the files in the
directory, control returns to the file that contained the #includedir directive.

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, but this will not catch the redefinition of an alias that is also present in a
different file.

Other special characters and reserved words
The pound sign (‘#’) is used to indicate a comment (unless it is part of a #include directive or unless it
occurs in the context of a user name and is followed by one or more digits, in which case it is treated as
a uid). Both the comment character and any text after it, up to the end of the line, are ignored.

The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever
one might otherwise use a 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_query_group_plugin
If a group_plugin is configured, use it to resolve groups of the form %group as long as
there is not also a system group of the same name. Normally, only groups of the form
%:group are passed to the group_plugin. This flag is off by default.

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 by default, HOME will be set to the home
directory of the target user when the env_reset option is enabled, so always_set_home
only has an effect 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) before they may run commands. This default may be overridden via the
PASSWD and NOPASSWD tags. This flag is on by default.

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

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.

exec_background By default, sudo runs a command as the foreground process as long as sudo itself is
running in the foreground. When the exec_background flag is enabled and the command is
being run in a pty (due to I/O logging or the use_pty flag), the command will be run as a
background process. Attempts to read from the controlling terminal (or to change
terminal settings) will result in the command being suspended with the SIGTTIN signal (or
SIGTTOU in the case of terminal settings). If this happens when sudo is a foreground
process, the command will be granted the controlling terminal and resumed in the
foreground with no user intervention required. The advantage of initially running the
command in the background is that sudo need not read from the terminal unless the command
explicitly requests it. Otherwise, any terminal input must be passed to the command,
whether it has required it or not (the kernel buffers terminals so it is not possible to
tell whether the command really wants the input). This is different from historic sudo
behavior or when the command is not being run in a pty.

For this to work seamlessly, the operating system must support the automatic restarting
of system calls. Unfortunately, not all operating systems do this by default, and even
those that do may have bugs. For example, macOS fails to restart the tcgetattr() and
tcsetattr() system calls (this is a bug in macOS). Furthermore, because this behavior
depends on the command stopping with the SIGTTIN or SIGTTOU signals, programs that catch
these signals and suspend themselves with a different signal (usually SIGTOP) will not be
automatically foregrounded. Some versions of the linux su(1) command behave this way.
This flag is off by default.

This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O
logging is enabled or the use_pty flag is enabled.

env_editor If set, visudo will use the value of the EDITOR or VISUAL environment variables before
falling back on the default editor list. Note that this may create a security hole as it
allows the user to run any arbitrary command as root without logging. A safer
alternative is to place a colon-separated list of editors in the editor variable. visudo
will then only use the EDITOR or VISUAL if they match a value specified in editor. If
the env_reset flag is enabled, the EDITOR and/or VISUAL environment variables must be
present in the env_keep list for the env_editor flag to function when visudo is invoked
via sudo. 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 or in the file specified by the restricted_env_file option 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 contents of the env_keep and
env_check lists, as modified by global Defaults parameters in sudoers, 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 implications 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 the sudoers file 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
host 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 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 on by default.

ignore_audit_errors
Allow commands to be run even if sudoers cannot write to the audit log. If enabled, an
audit log write failure is not treated as a fatal error. If disabled, a command may only
be run after the audit event is successfully written. This flag is only effective on
systems for which sudoers supports audit logging, including FreeBSD, Linux, macOS and
Solaris. This flag is on 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 off by default.

ignore_iolog_errors
Allow commands to be run even if sudoers cannot write to the I/O log. If enabled, an I/O
log write failure is not treated as a fatal error. If disabled, the command will be
terminated if the I/O log cannot be written to. This flag is off by default.

ignore_logfile_errors
Allow commands to be run even if sudoers cannot write to the log file. If enabled, a log
file write failure is not treated as a fatal error. If disabled, a command may only be
run after the log file entry is successfully written. This flag only has an effect when
sudoers is configured to use file-based logging via the logfile option. This flag is on
by default.

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

ignore_unknown_defaults
If set, sudo will not produce a warning if it encounters an unknown Defaults entry in the
sudoers file or an unknown sudoOption in LDAP. 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-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. For more information, see the I/O LOG FILES section. This flag is off by default.

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. For more information, see the I/O LOG FILES
section. This flag is off by default.

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

long_otp_prompt When validating with a One Time Password (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_all_cmnds Send mail to the mailto user every time a user attempts to run a command via sudo (this
includes sudoedit). No mail will be sent if the user runs sudo with the -l or -v option
unless there is an authentication error and the mail_badpass flag is also set. This flag
is off by default.

mail_always Send mail to the mailto user every time a user 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_all_cmnds, 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.

match_group_by_gid
By default, sudoers will look up each group the user is a member of by group ID to
determine the group name (this is only done once). The resulting list of the user's
group names is used when matching groups listed in the sudoers file. This works well on
systems where the number of groups listed in the sudoers file is larger than the number
of groups a typical user belongs to. On systems where group lookups are slow, where
users may belong to a large number of groups, and where the number of groups listed in
the sudoers file is relatively small, it may be prohibitively expensive and running
commands via sudo may take longer than normal. On such systems it may be faster to use
the match_group_by_gid flag to avoid resolving the user's group IDs to group names. In
this case, sudoers must look up any group name listed in the sudoers file and use the
group ID instead of the group name when determining whether the user is a member of the
group.

Note that if match_group_by_gid is enabled, group database lookups performed by sudoers
will be keyed by group name as opposed to group ID. On systems where there are multiple
sources for the group database, it is possible to have conflicting group names or group
IDs in the local /etc/group file and the remote group database. On such systems,
enabling or disabling match_group_by_gid can be used to choose whether group database
queries are performed by name (enabled) or ID (disabled), which may aid in working around
group entry conflicts.

The match_group_by_gid flag has no effect when sudoers data is stored in LDAP. This flag
is off by default.

This setting is only supported by version 1.8.18 or higher.

netgroup_tuple If set, netgroup lookups will be performed using the full netgroup tuple: host name, user
name and domain (if one is set). Historically, sudo only matched the user name and
domain for netgroups used in a User_List and only matched the host name and domain for
netgroups used in a Host_List. This flag is off by default.

noexec If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless
overridden by an EXEC tag. See the description of EXEC and NOEXEC above as well as the
Preventing shell escapes section at the end of this manual. This flag is off by default.

pam_session On systems that use PAM for authentication, sudo will create a new PAM session for the
command to be run in. Disabling pam_session may be needed on older PAM implementations
or on operating systems where opening a PAM session changes the utmp or wtmp files. If
PAM session support is disabled, resource limits may not be updated for the command being
run. If pam_session, pam_setcred, and use_pty are disabled and I/O logging has not been
configured, sudo will execute the command directly instead of running it as a child
process. This flag is on by default.

This setting is only supported by version 1.8.7 or higher.

pam_setcred On systems that use PAM for authentication, sudo will attempt to establish credentials
for the target user by default, if supported by the underlying authentication system.
One example of a credential is a Kerberos ticket. If pam_session, pam_setcred, and
use_pty are disabled and I/O logging has not been configured, sudo will execute the
command directly instead of running it as a child process. This flag is on by default.

This setting is only supported by version 1.8.8 or higher.

passprompt_override
If set, the prompt specified by passprompt or the SUDO_PROMPT environment variable will
always be used and will replace the prompt provided by a PAM module or other
authentication method. This flag is off by default.

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

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

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

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

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

rootpw If set, sudo will prompt for the root password instead of the password of the invoking
user when running a command or editing a file. 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 when running a command or
editing a file. 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 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 set_logname will have no effect if the
env_reset option has not been disabled and the env_keep list contains LOGNAME, USER or
USERNAME. 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, environment variables set via the command line are not subject to the
restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users
should be allowed to set variables in this manner. This flag is off by default.

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

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

sudoedit_checkdir
If set, sudoedit will check all directory components of the path to be edited for
writability by the invoking user. Symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a writable directory.
These restrictions are not enforced when sudoedit is run by root. On some systems, if
all directory components of the path to be edited are not readable by the target user,
sudoedit will be unable to edit the file. This flag is on by default.

This setting was first introduced in version 1.8.15 but initially suffered from a race
condition. The check for symbolic links in writable intermediate directories was added
in version 1.8.16.

sudoedit_follow By default, sudoedit will not follow symbolic links when opening files. The
sudoedit_follow option can be enabled to allow sudoedit to open symbolic links. It may
be overridden on a per-command basis by the FOLLOW and NOFOLLOW tags. This flag is off
by default.

This setting is only supported by version 1.8.15 or higher.

syslog_pid When logging via syslog(3), include the process ID in the log entry. This flag is off by
default.

This setting is only supported by version 1.8.21 or higher.

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 when running a command or
editing a file. 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 separate record in the time stamp file for each terminal. If disabled, a single
record is used for all login sessions.

This option has been superceded by the timestamp_type option.

umask_override If set, sudo will set the umask as specified in the sudoers file without modification.
This makes it possible to specify a umask in the sudoers file that is more permissive
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_netgroups If set, netgroups (prefixed with ‘+’), may be used in place of a user or host. For LDAP-
based sudoers, netgroup support requires an expensive substring match on the server
unless the NETGROUP_BASE directive is present in the /etc/sudo-ldap.conf file. If
netgroups are not needed, this option can be disabled to reduce the load on the LDAP
server. This flag is on 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.

user_command_timeouts
If set, the user may specify a timeout on the command line. If the timeout expires
before the command has exited, the command will be terminated. If a timeout is specified
both in the sudoers file and on the command line, the smaller of the two timeouts will be
used. See the Timeout_Spec section for a description of the timeout syntax. This flag
is off by default.

This setting is only supported by version 1.8.20 or higher.

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 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 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.

command_timeout The maximum amount of time a command is allowed to run before it is terminated. See the
Timeout_Spec section for a description of the timeout syntax.

This setting is only supported by version 1.8.20 or higher.

maxseq The maximum sequence number that will be substituted for the “%{seq}” escape in the I/O
log file (see the iolog_dir description above for more information). While the value
substituted for “%{seq}” is in base 36, maxseq itself should be expressed in decimal.
Values larger than 2176782336 (which corresponds to the base 36 sequence number “ZZZZZZ”)
will be silently truncated to 2176782336. The default value is 2176782336.

Once the local sequence number reaches the value of maxseq, it will “roll over” to zero,
after which sudoers will truncate and re-use any existing I/O log path names.

This setting is only supported by version 1.8.7 or higher.

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.

syslog_maxlen On many systems, syslog(3) has a relatively small log buffer. IETF RFC 5424 states that
syslog servers must support messages of at least 480 bytes and should support messages up
to 2048 bytes. By default, sudoers creates log messages up to 980 bytes which
corresponds to the historic BSD syslog implementation which used a 1024 byte buffer to
store the message, date, hostname and program name. To prevent syslog messages from
being truncated, sudoers will split up log messages that are larger than syslog_maxlen
bytes. When a message is split, additional parts will include the string “(command
continued)” after the user name and before the continued command line arguments.

This setting is only supported by version 1.8.19 or higher.

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 0.

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 15. Set this to 0 to always prompt for a password. If set to a
value less than 0 the user's time stamp will not expire until the system is rebooted.
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 value of the umask option, which defaults to 0022. This guarantees that sudo
never lowers the umask when running a command. Note: on systems that use PAM, the
default PAM configuration may specify its own umask which will override the value set in
sudoers.

Strings:

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

editor A colon (‘:’) separated list of editors allowed to be used with visudo. visudo will
choose the editor that matches the user's EDITOR or VISUAL environment variable if
possible, or the first editor in the list that exists and is executable. Note that the
EDITOR and VISUAL environment variables are not preserved by default when the env_reset
option is enabled. The default is /usr/bin/editor.

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 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.

If the path created by concatenating iolog_dir and iolog_file already exists, the
existing I/O log file will be truncated and overwritten unless iolog_file ends in six or
more Xs.

iolog_flush If set, sudo will flush I/O log data to disk after each write instead of buffering it.
This makes it possible to view the logs in real-time as the program is executing but may
significantly reduce the effectiveness of I/O log compression. This flag is off by
default.

This setting is only supported by version 1.8.20 or higher.

iolog_group The group name to look up when setting the group ID on new I/O log files and directories.
If iolog_group is not set, the primary group ID of the user specified by iolog_user is
used. If neither iolog_group nor iolog_user are set, I/O log files and directories are
created with group ID 0.

This setting is only supported by version 1.8.19 or higher.

iolog_mode The file mode to use when creating I/O log files. Mode bits for read and write
permissions for owner, group or other are honored, everything else is ignored. The file
permissions will always include the owner read and write bits, even if they are not
present in the specified mode. When creating I/O log directories, search (execute) bits
are added to to match the read and write bits specified by iolog_mode. Defaults to 0600
(read and write by user only).

This setting is only supported by version 1.8.19 or higher.

iolog_user The user name to look up when setting the user and group IDs on new I/O log files and
directories. If iolog_group is set, it will be used instead of the user's primary group
ID. By default, I/O log files and directories are created with user and group ID 0.

This setting can be useful when the I/O logs are stored on a Network File System (NFS)
share. Having a dedicated user own the I/O log files means that sudoers does not write
to the log files as user ID 0, which is usually not permitted by NFS.

This setting is only supported by version 1.8.19 or higher.

lecture_status_dir
The directory in which sudo stores per-user lecture status files. Once a user has
received the lecture, a zero-length file is created in this directory so that sudo will
not lecture the user again. This directory should not be cleared when the system
reboots. The default is /var/lib/sudo/lectured.

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 As of sudo version 1.8.1 this option is no longer supported. The path to the noexec file
should now be set in the sudo.conf(5) 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”. See the description of pam_service
for more information.

This setting is only supported by version 1.8.8 or higher.

pam_service On systems that use PAM for authentication, the service name specifies the PAM policy to
apply. This usually corresponds to an entry in the pam.conf file or a file in the
/etc/pam.d directory. The default value is “sudo”.

This setting is only supported by version 1.8.8 or higher.

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 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

On systems that use PAM for authentication, passprompt will only be used if the prompt
provided by the PAM module matches the string “Password: ” or “username's Password: ”.
This ensures that the passprompt setting does not interfere with challenge-response style
authentication. The passprompt_override flag can be used to change this behavior.

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 the sudoers file
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.

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”.

timestamp_type sudoers uses per-user time stamp files for credential caching. The timestamp_type option
can be used to specify the type of time stamp record used. It has the following possible
values:

global A single time stamp record is used for all of a user's login sessions, regardless
of the terminal or parent process ID. An additional record is used to serialize
password prompts when sudo is used multiple times in a pipeline, but this does
not affect authentication.

ppid A single time stamp record is used for all processes with the same parent process
ID (usually the shell). Commands run from the same shell (or other common parent
process) will not require a password for timestamp_timeout minutes (15 by
default). Commands run via sudo with a different parent process ID, for example
from a shell script, will be authenticated separately.

tty One time stamp record is used for each terminal, which means that a user's login
sessions are authenticated separately. If no terminal is present, the behavior
is the same as ppid. Commands run from the same terminal will not require a
password for timestamp_timeout minutes (15 by default).

The default value is tty.

This setting is only supported by version 1.8.21 or higher.

timestampdir The directory in which sudo stores its time stamp files. This directory should be
cleared when the system reboots. The default is /run/sudo/ts.

timestampowner The owner of the lecture status directory, time stamp directory and all files 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 the sudoers file
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 only added if the variable does not
already exist in the environment. This file is considered to be part of the security policy,
its contents are not subject to other sudo environment restrictions 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.

fdexec Determines whether sudo will execute a command by its path or by an open file descriptor. It
has the following possible values:

always Always execute by file descriptor.

never Never execute by file descriptor.

digest_only
Only execute by file descriptor if the command has an associated digest in the
sudoers file.

The default value is digest_only. This avoids a time of check versus time of use race
condition when the command is located in a directory writable by the invoking user.

Note that fdexec will change the first element of the argument vector for scripts ($0 in the
shell) due to the way the kernel runs script interpreters. Instead of being a normal path,
it will refer to a file descriptor. For example, /dev/fd/4 on Solaris and /proc/self/fd/4 on
Linux. A workaround is to use the SUDO_COMMAND environment variable instead.

The fdexec setting is only used when the command is matched by path name. It has no effect
if the command is matched by the built-in ALL alias.

This setting is only supported by version 1.8.20 or higher. If the operating system does not
support the fexecve(2) system call, this setting has no effect.

group_plugin A string containing a sudoers group plugin with optional arguments. The string should
consist of the plugin path, either fully-qualified or relative to the /usr/lib/sudo
directory, followed by any configuration arguments the plugin requires. These arguments (if
any) will be passed to the plugin's initialization function. If arguments are present, the
string must be enclosed in double quotes ("").

For more information see GROUP PROVIDER PLUGINS.

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 never.

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 file 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 file entries for the current host must have the
NOPASSWD flag set to avoid entering a password.

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

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

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

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

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

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

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

restricted_env_file
The restricted_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 only added if the
variable does not already exist in the environment. Unlike env_file, the file's contents are
not trusted and are processed in a manner similar to that of the invoking user's environment.
If env_reset is enabled, variables in the file will only be added if they are matched by
either the env_check or env_keep list. If env_reset is disabled, variables in the file are
added as long as they are not matched by the env_delete list. In either case, the contents
of restricted_env_file are processed before the contents of env_file.

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.

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

syslog_badpri
Syslog priority to use when the user is not allowed to run a command or when authentication
is unsuccessful. Defaults to alert.

The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice,
warning, and none. Negating the option or setting it to a value of none will disable logging
of unsuccessful commands.

syslog_goodpri
Syslog priority to use when the user is allowed to run a command and authentication is
successful. Defaults to notice.

See syslog_badpri for the list of supported syslog priorities. Negating the option or
setting it to a value of none will disable logging of successful commands.

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 file 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 file 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 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 vulnerabilities in poorly-written programs. The TZ variable is considered
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 disabled, variables specified by env_check will be preserved in the
environment if they pass the aforementioned check. The global 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 global 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 global list of
variables to keep is displayed when sudo is run by root with the -V option.

GROUP PROVIDER PLUGINS

The sudoers plugin supports its own plugin interface to allow non-Unix group lookups which can query a
group source other than the standard Unix group database. This can be used to implement support for the
nonunix_group syntax described earlier.

Group provider plugins are specified via the group_plugin Defaults setting. The argument to group_plugin
should consist of the plugin path, either fully-qualified or relative to the /usr/lib/sudo directory,
followed by any configuration options the plugin requires. These options (if specified) will be passed to
the plugin's initialization function. If options are present, the string must be enclosed in double quotes
("").

The following group provider plugins are installed by default:

group_file
The group_file plugin supports an alternate group file that uses the same syntax as the
/etc/group file. The path to the group file should be specified as an option to the plugin. For
example, if the group file to be used is /etc/sudo-group:

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

system_group
The system_group plugin supports group lookups via the standard C library functions getgrnam()
and getgrid(). This plugin can be used in instances where the user belongs to groups not present
in the user's supplemental group vector. This plugin takes no options:

Defaults group_plugin=system_group.so

The group provider plugin API is described in detail in sudo_plugin(5).

LOG FORMAT

sudoers can log events using either syslog(3) or a simple log file. The log format is almost identical in
both cases. Any control characters present in the log data are formatted in octal with a leading ‘#’
character. For example, a horizontal tab is stored as ‘#011’ and an embedded carriage return is stored as
‘#015’. In addition, space characters in the command path are stored as ‘#040’. Literal single quotes and
backslash characters (‘\’) in command line arguments are escaped with a backslash.

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 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, including any command line arguments.

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
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 setting, 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 the sudoers
file using group permissions to avoid this problem. Consider either changing the ownership of
/etc/sudoers or adding an argument like “sudoers_uid=N” (where ‘N’ is the user ID that owns the sudoers
file) to the end of the sudoers Plugin line in the sudo.conf(5) 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
sudo.conf(5) 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 sudo.conf(5) 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 sudo.conf(5) file.

unable to open /run/sudo/ts/username
sudoers was unable to read or create the user's time stamp file. This can happen when timestampowner is
set to a user other than root and the mode on /run/sudo is not searchable by group or other. The default
mode for /run/sudo is 0711.

unable to write to /run/sudo/ts/username
sudoers was unable to write to the user's time stamp file.

/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than timestampowner. This can occur when the value of
timestampowner has been changed. sudoers will ignore the time stamp directory until the owner is
corrected.

/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable only by timestampowner. The default
mode for the time stamp directory is 0700. sudoers will ignore the time stamp directory until the mode
is corrected.

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

The maximum size of syslog messages varies from system to system. The syslog_maxlen setting can be used to
change the maximum syslog message size from the default value of 980 bytes. For more information, see the
description of syslog_maxlen.

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 field is not present.

2. The hostname is only logged if the log_host option is enabled.

3. The date does not include the year unless the log_year option is enabled.

4. 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.

I/O LOG FILES

     When I/O logging is enabled, sudo will run the command in a pseudo-tty and log all user input and/or
     output.  I/O 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 sudo log line, prefixed with “TSID=”.  The iolog_file
     option may be used to control the format of the session ID.

     Each I/O log is stored in a separate directory that contains the following files:

     log       a text file containing the time the command was run, the name of the user who ran sudo, the name
               of the target user, the name of the target group (optional), the terminal that sudo was run from,
               the number of rows and columns of the terminal, the working directory the command was run from
               and the path name of the command itself (with arguments if present)

     timing    a log of the amount of time between, and the number of bytes in, each I/O log entry (used for
               session playback)

     ttyin     input from the user's tty (what the user types)

     stdin     input from a pipe or file

     ttyout    output from the pseudo-tty (what the command writes to the screen)

     stdout    standard output to a pipe or redirected to a file

     stderr    standard error to a pipe or redirected to a file

     All files other than log are compressed in gzip format unless the compress_io flag has been disabled.  Due
     to buffering, it is not normally possible to display the I/O logs in real-time as the program is executing
     The I/O log data will not be complete until the program run by sudo has exited or has been terminated by a
     signal.  The iolog_flush flag can be used to disable buffering, in which case I/O log data is written to
     disk as soon as it is available.  The output portion of an I/O log file can be viewed with the
     sudoreplay(8) utility, which can also be used to list or search the available logs.

     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, logging the command output
     via log_output or LOG_OUTPUT is all that is required.

     Since each session's I/O logs are stored in a separate directory, traditional log rotation utilities cannot
     be used to limit the number of I/O logs.  The simplest way to limit the number of I/O is by setting the
     maxseq option to the maximum number of logs you wish to store.  Once the I/O log sequence number reaches
     maxseq, it will be reset to zero and sudoers will truncate and re-use any existing I/O logs.

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

     /run/sudo/ts              Directory containing time stamps for the sudoers security policy

     /var/lib/sudo/lectured    Directory containing lecture status files for the sudoers security policy

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

EXAMPLES

     Below are example sudoers file 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,\
                             sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
                             /home/operator/bin/start_backups
     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).  Note that this will not effectively constrain users with sudo ALL
     privileges.

     # 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/.  Note that one command in the DUMPS Cmnd_Alias includes a sha224 digest,
     /home/operator/bin/start_backups.  This is because the directory containing the script is writable by the
     operator user.  If the script is modified (resulting in a digest mismatch) it will no longer be possible to
     run it via sudo.

     joe             ALL = /usr/bin/su operator

     The user joe may only su(1) 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.  Because command
     line arguments are matched as a single, concatenated string, the ‘*’ wildcard will match multiple words.
     This example assumes that passwd(1) does not take multiple user names on the command line.  Note that on
     GNU systems, options to passwd(1) may be specified after the user argument.  As a result, this rule will
     also allow:

         passwd username --expire

     which may not be desirable.

     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.  While not specifically mentioned in the rule,
     the commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the noexec option set.

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

     The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.

     matt            valkyrie = KILL

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

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

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

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

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

SECURITY NOTES

Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL using the ‘!’ operator. A user can trivially
circumvent this by copying the desired command to a different name and then executing that. For example:

bill ALL = ALL, !SU, !SHELLS

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

In general, if a user has sudo ALL there is nothing to prevent them from creating their own program that
gives them a root shell (or making their own copy of a shell) regardless of any ‘!’ elements in the user
specification.

Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably negate commands where the path name
includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3) function cannot
resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it
can result in a security issue for rules that subtract or revoke privileges.

For example, given the following sudoers file 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 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, 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 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 (see below).

Secure editing
The sudoers plugin includes sudoedit support which allows users to securely edit files with the editor of
their choice. As sudoedit is a built-in command, it must be specified in the sudoers file without a
leading path. However, it may take command line arguments just as a normal command does. Wildcards used
in sudoedit command line arguments are expected to be path names, so a forward slash (‘/’) will not be
matched by a wildcard.

Unlike other sudo commands, the editor is run with the permissions of the invoking user and with the
environment unmodified. More information may be found in the description of the -e option in sudo(8).

For example, to allow user operator to edit the “message of the day” file:

operator sudoedit /etc/motd

The operator user then runs sudoedit as follows:

$ sudoedit /etc/motd

The editor will run as the operator user, not root, on a temporary copy of /etc/motd. After the file has
been edited, /etc/motd will be updated with the contents of the temporary copy.

Users should never be granted sudoedit permission to edit a file that resides in a directory the user has
write access to, either directly or via a wildcard. If the user has write access to the directory it is
possible to replace the legitimate file with a link to another file, allowing the editing of arbitrary
files. To prevent this, starting with version 1.8.16, symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a writable directory unless the
sudoedit_checkdir option has been disabled or the invoking user is root. Additionally, in version 1.8.15
and higher, sudoedit will refuse to open a symbolic link unless either the sudoedit_follow option is
enabled or the sudoedit command is prefixed with the FOLLOW tag in the sudoers file.

Time stamp file checks
sudoers will check the ownership of its time stamp directory (/run/sudo/ts by default) and ignore the
directory's contents if it is not owned by root or if it is writable by a user other than root. Older
versions of sudo stored time stamp files in /tmp; this is no longer recommended as it may be possible for a
user to create the time stamp themselves on systems that allow unprivileged users to change the ownership
of files they create.

While the time stamp directory should be cleared at reboot time, not all systems contain a /var/run
directory. To avoid potential problems, sudoers will ignore time stamp files that date from before the
machine booted on systems where the boot time is available.

Some systems with graphical desktop environments allow unprivileged users to change the system clock.
Since sudoers relies on the system clock for time stamp validation, it may be possible on such systems for
a user to run sudo for longer than timestamp_timeout by setting the clock back. To combat this, sudoers
uses a monotonic clock (which never moves backwards) for its time stamps if the system supports it.

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 sudoers will log and complain.

Since time stamp files live in the file system, they can outlive a user's login session. As a result, a
user may be able to login, run a command with sudo after authenticating, logout, login again, and run sudo
without authenticating so long as the record's time stamp is within 15 minutes (or whatever value the
timeout is set to in the sudoers file). When the tty_tickets option is enabled, the time stamp record
includes the device number of the terminal the user authenticated with. This provides per-tty granularity
but time stamp records still may outlive the user's session. The time stamp record also includes the
session ID of the process that last authenticated. This prevents processes in different terminal sessions
from using the same time stamp record. It also helps reduce the chance that a user will be able to run
sudo without entering a password when logging out and back in again on the same terminal.

DEBUGGING

     Versions 1.8.4 and higher of the sudoers plugin support a flexible debugging framework that can help track
     down what the plugin is doing internally if there is a problem.  This can be configured in the sudo.conf(5)
     file.

     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 the sudoers plugin:

     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 file Defaults settings

     env       environment handling

     ldap      LDAP-based sudoers

     logging   logging support

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

     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

     sssd      SSSD-based sudoers

     util      utility functions
     For example:

     Debug sudo /var/log/sudo_debug match@info,nss@info

     For more information, see the sudo.conf(5) manual.

AUTHORS

     Many people have worked on sudo over the years; this version consists of code written primarily by:

           Todd C. Miller

     See the CONTRIBUTORS file in the sudo distribution (https://www.sudo.ws/contributors.html) for an
     exhaustive list of people who have contributed to sudo.

CAVEATS

     The sudoers file should always be edited by the visudo command which locks the file and does grammatical
     checking.  It is imperative that the sudoers file be free of syntax errors since sudo will not run with a
     syntactically 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 https://bugzilla.sudo.ws/

SUPPORT

     Limited free support is available via the sudo-users mailing list, see
     https://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
     warranties of merchantability and fitness for a particular purpose are disclaimed.  See the LICENSE file
     distributed with sudo or https://www.sudo.ws/license.html for complete details.

NAME

DESCRIPTION

SUDOERS FILE FORMAT

SUDOERS OPTIONS

GROUP PROVIDER PLUGINS

LOG FORMAT

I/O LOG FILES

FILES

EXAMPLES

SECURITY NOTES

DEBUGGING

SEE ALSO

AUTHORS

CAVEATS

BUGS

SUPPORT

DISCLAIMER