Ubuntu Manpage: sudoers — default sudo security policy plugin

Provided by: sudo-ldap_1.9.14p2-1ubuntu1_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, see sudoers.ldap(5).

Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which plugins to load. If no sudo.conf(5)
file is present, or if it contains no Plugin lines, sudoers will be used for auditing,
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_audit sudoers.so
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. Plugin arguments, if any, should be listed after the path to the
plugin (i.e., after sudoers.so). The arguments are only effective for the plugin that opens
(and parses) the sudoers file.

For sudo version 1.9.1 and higher, this is the sudoers_audit plugin. For older versions, it
is the sudoers_policy plugin. Multiple arguments may be specified, separated by white
space. For example:

Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false

The following plugin arguments are supported:

error_recovery=bool
The error_recovery argument can be used to control whether sudoers should attempt to
recover from syntax errors in the sudoers file. If set to true (the default), sudoers
will try to recover from a syntax error by discarding the portion of the line that
contains the error until the end of the line. A value of false will disable error
recovery. Prior to version 1.9.3, no error recovery was performed.

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

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), 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.

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. By default, all attempts to run sudo (successful or not) are 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, the start time of the session leader (or parent process) 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
By default, sudoers logs both successful and unsuccessful attempts (as well as errors). The
log_allowed and log_denied flags can be used to control this behavior. Messages can be
logged to syslog(3), a log file, or both. The default is to log to syslog(3) but this is
configurable via the syslog and logfile settings. See EVENT LOGGING for a description of
the log file format.

sudoers is also capable of running a command in a pseudo-terminal and logging input and/or
output. The standard input, standard output, and standard error can be logged even when not
associated with a terminal. For more information about I/O logging, see the I/O LOGGING
section.

Starting with version 1.9, the log_servers setting may be used to send event and I/O log
data to a remote server running sudo_logsrvd or another service that implements the protocol
described by sudo_logsrv.proto(5).

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 flag 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 HOME, MAIL, SHELL, LOGNAME and USER
environment variables are initialized based on the target user and the SUDO_* variables are
set based on the invoking user. Additional variables, such as DISPLAY, PATH and TERM, are
preserved from the invoking user's environment if permitted by the env_check, or env_keep
options. A few environment variables are treated specially. If the PATH and TERM variables
are not preserved from the user's environment, they will be set to default values. The
LOGNAME and USER are handled as a single entity. If one of them is preserved (or removed)
from the user's environment, the other will be as well. If LOGNAME and USER are to be
preserved but only one of them is present in the user's environment, the other will be set
to the same value. This avoids an inconsistent environment where one of the variables
describing the user name is set to the invoking user and one is set to the target user.
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 flag is disabled, any variables not explicitly denied by the
env_check and env_delete options are allowed and their values are inherited from the
invoking process. 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 block 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 are preserved or removed, as modified by
global Defaults parameters in sudoers, is displayed when sudo is run by root with the -V
option. The list of environment variables to remove varies based on the operating system
sudo is running on.

Other settings may influence the command environment:

• sudoers options such as always_set_home, secure_path, set_logname, set_home, and setenv.

• Command tags, such as SETENV and NOSETENV. Note that SETENV is implied if the command
matched is ALL.

• sudo options, such as -E and -i.

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.

The dynamic linker on most operating systems will remove variables that can control dynamic
linking from the environment of set-user-ID 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 the -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 unless permitted by env_keep or env_check,
described above.

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.

Resource limits
By default, sudoers uses the operating system's native method of setting resource limits for
the target user. On Linux systems, resource limits are usually set by the pam_limits.so PAM
module. On some BSD systems, the /etc/login.conf file specifies resource limits for the
user. On AIX systems, resource limits are configured in the /etc/security/limits file. If
there is no system mechanism to set per-user resource limits, the command will run with the
same limits as the invoking user. The one exception to this is the core dump file size,
which is set by sudoers to 0 by default. Disabling core dumps by default makes it possible
to avoid potential security problems where the core file is treated as trusted input.

Resource limits may also be set in the sudoers file itself, in which case they override
those set by the system. See the rlimit_as, rlimit_core, rlimit_cpu, rlimit_data,
rlimit_fsize, rlimit_locks, rlimit_memlock, rlimit_nofile, rlimit_nproc, rlimit_rss,
rlimit_stack options described below. Resource limits in sudoers may be specified in one of
the following formats:

“value”
Both the soft and hard resource limits are set to the same value. The special value
“infinity” can be used to indicate that the value is unlimited.

“soft,hard”
Two comma-separated values. The soft limit is set to the first value and the hard
limit is set to the second. Both values must either be enclosed in a set of double
quotes, or the comma must be escaped with a backslash (‘\’). The special value
“infinity” may be used in place of either value.

“default”
The default resource limit for the user will be used. This may be a user-specific
value (see above) or the value of the resource limit when sudo was invoked for
systems that don't support per-user limits.

“user” The invoking user's resource limits will be preserved when running the command.

For example, to restore the historic core dump file size behavior, a line like the following
may be used.

Defaults rlimit_core=default

Resource limits in sudoers are only supported by version 1.8.7 or higher.

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. For example:

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.
Beginning with sudo 1.9.0, Cmd_Alias may be used in place of Cmnd_Alias if desired.

Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*

User_Alias ::= NAME

User_Alias_Spec ::= User_Alias '=' User_List

Runas_Alias ::= NAME

Runas_Alias_Spec ::= Runas_Alias '=' Runas_List

Host_Alias ::= NAME

Host_Alias_Spec ::= Host_Alias '=' Host_List

Cmnd_Alias ::= NAME

Cmnd_Alias_Spec ::= Cmnd_Alias '=' 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 (‘:’). For example:

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, user-ID, group, group-ID, 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.

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. User names and groups are matched as strings. In other words, two users
(groups) with the same user (group) ID are considered to be distinct. If you wish to match
all user names with the same user-ID (e.g., root and toor), you can use a user-ID instead of
a name (#0 in the example given). The user-ID or group-ID specified in a Runas_Member need
not be listed in the password or group database.

Host_List ::= Host |
Host ',' Host_List

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 hostname command on your machine returns the fully qualified
host name, you'll need to use the fqdn flag for wildcards to be useful. 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

Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List

Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List

command name ::= regex |
file name

command ::= command name |
command name args |
command name regex |
command name '""' |
ALL

Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"

List_Spec ::= "list"

Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_Alias

A Cmnd_List is a list of one or more commands, directories, or aliases. A command is a
fully qualified file name, which may include shell-style wildcards (see the Wildcards
section below), or a regular expression that starts with ‘^’ and ends with ‘$’ (see the
Regular expressions section below). A directory is a fully qualified path name ending in a
‘/’. When you specify a directory in a Cmnd_List, the user will be able to run any file
within that directory (but not in any sub-directories therein). If no command line
arguments are specified, the user may run the command with any arguments they choose.
Command line arguments can include wildcards or be a regular expression that starts with ‘^’
and ends with ‘$’. If the command line arguments consist of ‘""’, the command may only be
run with no arguments.

If a Cmnd has associated command line arguments, the arguments in the Cmnd must match those
given by the user on the command line. If the arguments in a Cmnd begin with the ‘^’
character, they will be interpreted as a regular expression and matched accordingly.
Otherwise, shell-style wildcards are used when matching. Unless a regular expression is
specified, the following characters must be escaped with a ‘\’ if they are used in command
arguments: ‘,’, ‘:’, ‘=’, ‘\’. To prevent arguments in a Cmnd that begin with a ‘^’
character from being interpreted as a regular expression, the ‘^’ must be escaped with a
‘\’.

There are two commands built into sudo itself: “list” and “sudoedit”. Unlike other
commands, these two must be specified in the sudoers file without a leading path.

The “list” built-in can be used to permit a user to list another user's privileges with
sudo's -U option. For example, “sudo -l -U otheruser”. A user with the “list” privilege is
able to list another user's privileges even if they don't have permission to run commands as
that user. By default, only root or a user with the ability to run any command as either
root or the specified user on the current host may use the -U option. No command line
arguments may be specified with the “list” built-in.

The “sudoedit” built-in 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. Unlike other
commands, “sudoedit” is built into sudo itself and must be specified in the sudoers file
without a leading path. If a leading path is present, for example /usr/bin/sudoedit, the
path name will be silently converted to “sudoedit”. A fully-qualified path for sudoedit is
treated as an error by visudo.

A command may be preceded by a Digest_List, a comma-separated list of one or more
Digest_Spec entries. If a Digest_List is present, the command will only match successfully
if it can be verified using one of the SHA-2 digests in the list. Starting with version
1.9.0, the ALL reserved word can be used in conjunction with a Digest_List. 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 (‘Defaults’), all users
on a specific host (‘Defaults@host’), a specific user (‘Defaults:user’), a specific command
(‘Defaults!cmnd’), or commands being run as a specific user (‘Defaults>runasuser’).

White space is not permitted between ‘Defaults’ and the ‘@’, ‘:’, ‘!’, or ‘>’ characters.
While a comma-separated list may be used in place of a single value after the ‘@’, ‘:’, ‘!’,
or ‘>’ character, using an alias instead of a list is often improve readability. 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
(‘\’).

To include a literal backslash character in a command line argument you must escape the
backslash twice. For example, to match ‘\n’ as part of a command line argument, you must
use ‘\\\\n’ in the sudoers file. This is due to there being two levels of escaping, one in
the sudoers parser itself and another when command line arguments are matched by the
fnmatch(3) or regexec(3) function.

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: global, 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 | Chdir_Spec | Chroot_Spec)

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

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

Timeout_Spec ::= 'TIMEOUT=timeout'

Chdir_Spec ::= 'CWD=directory'

Chroot_Spec ::= 'CHROOT=directory'

A user specification determines which commands a user may run (and as what user) on
specified hosts. By default, commands are run as root (unless runas_default has been set to
a different value) but this can also 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 the -u option. The second defines a list of groups that may be
specified via the -g option (in addition to any of the target user's groups). 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 and, optionally, with any group the target user belongs to. 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 and the group, if specified, must be
one that the invoking user is a member of. If no Runas_Spec is specified, the command may
only be run as the runas_default user (root by default) and the group, if specified, must be
one that the runas_default user is a member of.

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. For example:

$ 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

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

In this example only the group will be set, the command still runs as user tcm. For
example:

$ 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. Options may consist of SELinux
roles and/or types, start and/or end dates 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. Option names are reserved words in sudoers. This means that none of the
valid option names (see below) can be used when declaring an alias.

SELinux_Spec
On systems with SELinux support, sudoers file entries may optionally have an SELinux role
and/or type associated with a command. This can be used to implement a form of role-based
access control (RBAC). 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 setting is only supported by version 1.8.20 or higher.

Chdir_Spec
The working directory that the command will be run in can be specified using the CWD
setting. The directory must be a fully-qualified path name beginning with a ‘/’ or ‘~’
character, or the special value “*”. A value of “*” indicates that the user may specify the
working directory by running sudo with the -D option. By default, commands are run from the
invoking user's current working directory, unless the -i option is given. Path names of the
form ~user/path/name are interpreted as being relative to the named user's home directory.
If the user name is omitted, the path will be relative to the runas user's home directory.

This setting is only supported by version 1.9.3 or higher.

Chroot_Spec
The root directory that the command will be run in can be specified using the CHROOT
setting. The directory must be a fully-qualified path name beginning with a ‘/’ or ‘~’
character, or the special value “*”. A value of “*” indicates that the user may specify the
root directory by running sudo with the -R option. This setting can be used to run the
command in a chroot(2) “sandbox” similar to the chroot(8) utility. Path names of the form
~user/path/name are interpreted as being relative to the named user's home directory. If
the user name is omitted, the path will be relative to the runas user's home directory.

This setting is only supported by version 1.9.3 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, INTERCEPT, NOINTERCEPT, 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 flag 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 flag on a per-command basis. For more
information, see I/O LOGGING.

LOG_OUTPUT and NOLOG_OUTPUT

These tags override the value of the log_output flag on a per-command basis. For more
information, see I/O LOGGING.

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 flag 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 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 setting.

By default, if the NOPASSWD tag is applied to any of a user's entries for the current
host, the user will be able to run ‘sudo -l’ without a password. Additionally, a user may
only run ‘sudo -v’ without a password if all of the user's entries for the current host
have the NOPASSWD tag. This behavior may be overridden via the verifypw and listpw
options.

SETENV and NOSETENV

These tags override the value of the setenv flag on a per-command basis. If SETENV has
been set for a command, the user may disable the env_reset flag 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.

INTERCEPT and NOINTERCEPT

If sudo has been compiled with intercept support and the underlying operating system
supports it, the INTERCEPT tag can be used to cause programs spawned by a command to be
validated against sudoers and logged just like they would be if run through sudo directly.
This is useful in conjunction with commands that allow shell escapes such as editors,
shells, and paginators. There is additional overhead due to the policy check that may add
latency when running commands such as shell scripts that execute a large number of sub-
commands. For interactive commands, such as a shell or editor, the overhead is not
usually noticeable.

In the following example, user chuck may run any command on the machine “research” in
intercept mode.

chuck research = INTERCEPT: ALL

See the Preventing shell escapes section below for more details on how INTERCEPT works and
whether or not it will work on your system.

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 ‘]’.

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.

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.
Wildcards can match any character, including white space. In most cases, it is safer to use
a regular expression to match command line arguments. For more information, see Wildcards
in command arguments below.

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.

Regular expressions
Starting with version 1.9.10, it is possible to use regular expressions for path names and
command line arguments. Regular expressions are more expressive than shell-style wildcards
and are usually safer because they provide a greater degree of control when matching. The
type of regular expressions supported by sudoers are POSIX extended regular expressions,
similar to those used by the egrep(1) utility. They are usually documented in the regex(7)
or re_format(7) manual, depending on the system. As an extension, if the regular expression
begins with “(?i)”, it will be matched in a case-insensitive manner.

In sudoers, regular expressions must start with a ‘^’ character and end with a ‘$’. This
makes it explicit what is, or is not, a regular expression. Either the path name, the
command line arguments or both may be regular expressions. Because the path name and
arguments are matched separately, it is even possible to use wildcards for the path name and
regular expressions for the arguments. It is not possible to use a single regular
expression to match both the command and its arguments. Regular expressions in sudoers are
limited to 1024 characters.

There is no need to escape sudoers special characters in a regular expression other than the
pound sign (‘#’).

In the following example, user john can run the passwd(1) command as root on any host but is
not allowed to change root's password. This kind of rule is impossible to express safely
using wildcards.

john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd root

It is also possible to use a regular expression in conjunction with sudoedit rules. The
following rule would give user bob the ability to edit the /etc/motd, /etc/issue, and
/etc/hosts files only.

bob ALL = sudoedit ^/etc/(motd|issue|hosts)$

Regular expressions may also be used to match the command itself. In this example, a
regular expression is used to allow user sid to run the /usr/sbin/groupadd,
/usr/sbin/groupmod, /usr/sbin/groupdel, /usr/sbin/useradd, /usr/sbin/usermod, and
/usr/sbin/userdel commands as root.

sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$

One disadvantage of using a regular expression to match the command name is that it is not
possible to match relative paths such as ./useradd or ../sbin/useradd. This has security
implications when a regular expression is used for the command name in conjunction with the
negation operator, ‘!’, as such rules can be trivially bypassed. Because of this, using a
negated regular expression for the command name is strongly discouraged. This does not
apply to negated commands that only use a regular expression to match the command arguments.
See Regular expressions in command names below for more information.

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. For compatibility with sudo versions
prior to 1.9.1, #include and #includedir are also accepted.

An include file 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 one 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.

Starting with version 1.9.1, the path to the include file may contain white space if it is
escaped with a backslash (‘\’). Alternately, the entire path may be enclosed in double
quotes (""), in which case no escaping is necessary. To include a literal backslash in the
path, ‘\\’ should be used.

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.

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 user-ID). 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.
Attempting to define an alias named ALL will result in a syntax error. Using ALL can be
dangerous since in a command context, it allows the user to run any command on the system.

The following option names permitted in an Option_Spec are also considered reserved words:
CHROOT, ROLE, TYPE, TIMEOUT, CWD, NOTBEFORE and NOTAFTER. Attempting to define an alias
with the same name as one of the options will result in a syntax error.

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 the runas_default user unless the
-u option is used). This flag is largely obsolete and has no effect
unless the env_reset flag has been disabled or HOME is present in the
env_keep list, both of which are strongly discouraged. 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.

case_insensitive_group
If enabled, group names in sudoers will be matched in a case insensitive
manner. This may be necessary when users are stored in LDAP or AD. This
flag is on by default.

case_insensitive_user
If enabled, user names in sudoers will be matched in a case insensitive
manner. This may be necessary when groups are stored in LDAP or AD. This
flag is on by default.

closefrom_override
If set, the user may use the -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 pseudo-terminal (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 pseudo-terminal.

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(3) and tcsetattr(3)
functions (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 SUDO_EDITOR, VISUAL or EDITOR
environment variables before falling back on the default editor list.
visudo is typically run as root so this flag may allow a user with visudo
privileges to run arbitrary commands as root without logging. An
alternative is to place a colon-separated list of “safe” editors int the
editor setting. visudo will then only use SUDO_EDITOR, VISUAL or EDITOR
if they match a value specified in editor. If the env_reset flag is
enabled, the SUDO_EDITOR, VISUAL and/or EDITOR 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 and SUDO_* variables. Any
variables in the caller's environment or in the file specified by the
restricted_env_file setting 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 setting (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 setting
is enabled, 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 flag 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 paths
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 flag 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.

log_passwords Most programs that require a user's password will disable echo before
reading the password to avoid displaying the plaintext password on the
screen. However, if terminal input is being logged (see I/O LOGGING), the
password will still be present in the I/O log. If the log_passwords
option is disabled, sudoers will attempt to prevent passwords from being
logged. It does this by using the regular expressions in passprompt_regex
to match a password prompt in the terminal output buffer. When a match is
found, input characters in the I/O log will be replaced with ‘*’ until
either a line feed or carriage return is found in the terminal input or a
new terminal output buffer is received. If, however, a program displays
characters as the user types (such as sudo when pwfeedback is set), only
the first character of the password will be replaced in the I/O log. This
option has no effect unless log_input or log_ttyin are also set. This
flag is on by default.

This setting is only supported by version 1.9.10 or higher.

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 flag is only effective when the “canonical”
host name, as returned by the getaddrinfo(3) or gethostbyname(3) 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 flag
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). 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 the 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
(local or remote). 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 setting. This flag
is on by default.

ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be skipped. This is
intended for sites 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 flag is
enabled, /etc/sudoers does not even need to exist. Since this flag 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_allowed If set, sudoers will log commands allowed by the policy to the system
audit log (where supported) as well as to syslog and/or a log file. This
flag is on by default.

This setting is only supported by version 1.8.29 or higher.

log_denied If set, sudoers will log commands denied by the policy to the system audit
log (where supported) as well as to syslog and/or a log file. This flag
is on by default.

This setting is only supported by version 1.8.29 or higher.

log_exit_status If set, sudoers will log the exit value of commands that are run to syslog
and/or a log file. If a command was terminated by a signal, the signal
name is logged as well. This flag is off by default.

This setting is only supported by version 1.9.8 or higher.

log_host If set, the host name will be included in log entries written to the file
configured by the logfile setting. This flag is off by default.

log_input If set, sudo will run the command in a pseudo-terminal (if sudo was run
from a terminal) and log all user input. If the standard input is not
connected to the user's terminal, due to I/O redirection or because the
command is part of a pipeline, that input is also logged. For more
information about I/O logging, see the I/O LOGGING section. This flag is
off by default.

log_output If set, sudo will run the command in a pseudo-terminal (if sudo was run
from a terminal) and log all output that is sent to the user's terminal,
the standard output or the standard error. If the standard output or
standard error is not connected to the user's terminal, due to I/O
redirection or because the command is part of a pipeline, that output is
also logged. For more information about I/O logging, see the I/O LOGGING
section. This flag is off by default.

log_server_keepalive
If set, sudo will enable the TCP keepalive socket option on the connection
to the log server. This enables the periodic transmission of keepalive
messages to the server. If the server does not respond to a message, the
connection will be closed and the running command will be terminated
unless the ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set. This flag is on by
default.

This setting is only supported by version 1.9.0 or higher.

log_server_verify
If set, the server certificate received during the TLS handshake must be
valid and it must contain either the server name (from log_servers) or its
IP address. If either of these conditions is not met, the TLS handshake
will fail. This flag is on by default.

This setting is only supported by version 1.9.0 or higher.

log_stderr If set, sudo will log the standard error if it is not connected to the
user's terminal. This can be used to log output to a pipe or redirected
to a file. This flag is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.

log_stdin If set, sudo will log the standard input if it is not connected to the
user's terminal. This can be used to log input from a pipe or redirected
from a file. This flag is off by default but is enabled when either the
log_input flag or the LOG_INPUT command tag is set.

log_stdout If set, sudo will log the standard output if it is not connected to the
user's terminal. This can be used to log output to a pipe or redirected
to a file. This flag is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.

log_subcmds If set, sudoers will log when a command spawns a child process and
executes a program using the execve(2), execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), or system(3) library functions. For
example, if a shell is run by sudo, the individual commands run via the
shell will be logged. This flag is off by default.

The log_subcmds flag uses the same underlying mechanism as the intercept
setting. See Preventing shell escapes for more information on what
systems support this option and its limitations. This setting is only
supported by version 1.9.8 or higher and is incompatible with SELinux RBAC
support unless the system supports seccomp(2) filter mode.

log_ttyin If set, sudo will run the command in a pseudo-terminal and log user
keystrokes sent to the user's terminal, if one is present. This flag is
off by default but is enabled when either the log_input flag or the
LOG_INPUT command tag is set. If no terminal is present, for example when
running a remote command using ssh(1), this flag will have no effect.

log_ttyout If set, sudo will run the command in a pseudo-terminal and log all output
displayed on the user's terminal, if one is present. This flag is off by
default but is enabled when either the log_output flag or the LOG_OUTPUT
command tag is set. If no terminal is present, for example when running a
remote command using ssh(1), this flag will have no effect.

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, or 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.

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.

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

This setting is only supported by version 1.9.8 or higher and is
incompatible with SELinux RBAC support unless the system supports
seccomp(2) filter mode.

intercept_allow_setid
On most systems, the dynamic loader will ignore LD_PRELOAD (or the
equivalent) when running set-user-ID and set-group-ID programs,
effectively disabling intercept mode. To prevent this from happening,
sudoers will not permit a set-user-ID or set-group-ID program to be run in
intercept mode unless intercept_allow_setid is enable. This flag has no
effect unless the intercept flag is enabled or the INTERCEPT tag has been
set for the command. This flag is on by default when the intercept_type
option is set to trace, otherwise it default to off.

This setting is only supported by version 1.9.8 or higher.

intercept_authenticate
If set, commands run by an intercepted process must be authenticated when
the user's time stamp is not current. For example, if a shell is run with
intercept enabled, as soon as the invoking user's time stamp is out of
date, subsequent commands will need to be authenticated. This flag has no
effect unless the intercept flag is enabled or the INTERCEPT tag has been
set for the command. This flag is off by default.

This setting is only supported by version 1.9.8 or higher.

intercept_verify If set, sudo will attempt to verify that a command run in intercept mode
has the expected path name, command line arguments and environment.

The process will be stopped after execve(2) has completed but before the
new command has had a chance to run. To verify the command, sudo will
read the command's path from /proc/PID/exe, the command line arguments and
environment from the process's memory, and compare them against the
arguments that were passed to execve(2). In the event of a mismatch, the
command will be sent a SIGKILL signal and terminated.

This can help prevent a time of check versus time of use issue with
intercept mode where the execve(2) arguments could be altered after the
sudoers policy check. The checks can only be performed if the proc(5)
file system is available. This flag has no effect unless the intercept
flag is enabled or the INTERCEPT tag has been set for the command and the
intercept_type option is set to trace. This flag is on by default.

This setting is only supported by version 1.9.12 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.

noninteractive_auth
If set, authentication will be attempted even in non-interactive mode
(when sudo's -n option is specified). This allows authentication methods
that don't require user interaction to succeed. Authentication methods
that require input from the user's terminal will still fail. If disabled,
authentication will not be attempted in non-interactive mode. This flag
is off by default.

This setting is only supported by version 1.9.10 or higher.

pam_acct_mgmt On systems that use PAM for authentication, sudo will perform PAM account
validation for the invoking user by default. The actual checks performed
depend on which PAM modules are configured. If enabled, account
validation will be performed regardless of whether or not a password is
required. This flag is on by default.

This setting is only supported by version 1.8.28 or higher.

pam_rhost On systems that use PAM for authentication, sudo will set the PAM remote
host value to the name of the local host when the pam_rhost flag is
enabled. On Linux systems, enabling pam_rhost may result in DNS lookups
of the local host name when PAM is initialized. On Solaris versions prior
to Solaris 8, pam_rhost must be enabled if pam_ruser is also enabled to
avoid a crash in the Solaris PAM implementation.

This flag is off by default on systems other than Solaris.

This setting is only supported by version 1.9.0 or higher.

pam_ruser On systems that use PAM for authentication, sudo will set the PAM remote
user value to the name of the user that invoked sudo when the pam_ruser
flag is enabled. This flag is on by default.

This setting is only supported by version 1.9.0 or higher.

pam_session On systems that use PAM for authentication, sudo will create a new PAM
session for the command to be run in. Unless sudo is given the -i or -s
options, PAM session modules are run with the “silent” flag enabled. This
prevents last login information from being displayed for every command on
some systems. 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, log_servers has not
been set 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, log_servers has not
been set 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. 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.

runas_allow_unknown_id
If enabled, allow matching of runas user and group IDs that are not
present in the password or group databases. In addition to explicitly
matching unknown user or group IDs in a Runas_List, this option also
allows the ALL alias to match unknown IDs. This flag is off by default.

This setting is only supported by version 1.8.30 or higher. Older
versions of sudo always allowed matching of unknown user and group IDs.

runas_check_shell
If enabled, sudo will only run commands as a user whose shell appears in
the /etc/shells file, even if the invoking user's Runas_List would
otherwise permit it. If no /etc/shells file is present, a system-
dependent list of built-in default shells is used. On many operating
systems, system users such as “bin”, do not have a valid shell and this
flag can be used to prevent commands from being run as those users. This
flag is off by default.

This setting is only supported by version 1.8.30 or higher.

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.

selinux If enabled, the user may specify an SELinux role and/or type to use when
running the command, as permitted by the SELinux policy. If SELinux is
disabled on the system, this flag has no effect. This flag is on 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
the runas_default user unless the -u option is used). This flag is
largely obsolete and has no effect unless the env_reset flag has been
disabled or HOME is present in the env_keep list, both of which are
strongly discouraged. This flag is off by default.

set_logname Normally, sudo will set the LOGNAME and USER environment variables to the
name of the target user (the user specified by runas_default 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. The set_logname option will have no
effect if the env_reset option has not been disabled and the env_keep list
contains LOGNAME or USER. This flag is on by default.

set_utmp When enabled, sudo will create an entry in the utmp (or utmpx) file when a
pseudo-terminal is allocated. A pseudo-terminal is allocated by sudo when
it is running in a terminal and one or more of the log_input, log_output,
log_stdin, log_stdout, log_stderr, log_ttyin, log_ttyout, or use_pty flags
is 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 user-IDs are
set to the target user (root by default). This option changes that
behavior such that the real user-ID is left as the invoking user's user-
ID. In other words, this makes sudo act as a set-user-ID wrapper. This
can be useful on systems that disable some potentially dangerous
functionality when a program is run set-user-ID. 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 the value of runas_default) instead of the password of
the invoking user when running a command or editing a file. This flag
precludes the use of a user-ID 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 superseded 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 sub-
string 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, and sudo is running in a terminal, the command will be run in a
new pseudo-terminal. If the sudo process is not attached to a terminal,
use_pty has no effect.

A malicious program run under sudo may be capable of injecting commands
into the user's terminal or running a background process that retains
access to the user's terminal device even after the main program has
finished executing. By running the command in a separate pseudo-terminal,
this attack is no longer possible. This flag is on by default for sudo
1.9.14 and above.

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 (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.

log_server_timeout
The maximum amount of time to wait when connecting to a log server or
waiting for a server response. See the Timeout_Spec section for a
description of the timeout syntax. The default value is 30 seconds.

This setting is only supported by version 1.9.0 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 below 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 password
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 File mode creation mask to use when running the command. Negate this
option or set it to 0777 to prevent sudoers from changing the umask.
Unless the umask_override flag is set, the actual umask will be the union
of the user's umask and the value of the umask setting, which defaults to
0022. This guarantees that sudo never lowers the umask when running a
command.

If umask is explicitly set in sudoers, it will override any umask setting
in PAM or login.conf. If umask is not set in sudoers, the umask specified
by PAM or login.conf will take precedence. The umask setting in PAM is
not used for sudoedit, which does not create a new PAM session.

Strings:

authfail_message Message that is displayed after a user fails to authenticate. The message
may include the ‘%d’ escape which will expand to the number of failed
password attempts. If set, it overrides the default message, “%d
incorrect password attempt(s)”.

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 editor path names used by sudoedit and
visudo. For sudoedit, this list is used to find an editor when none of
the SUDO_EDITOR, VISUAL or EDITOR environment variables are set to an
editor that exists and is executable. For visudo, it is used as a white
list of allowed editors; visudo will choose the editor that matches the
user's SUDO_EDITOR, VISUAL or EDITOR environment variable if possible, or
the first editor in the list that exists and is executable if not. Unless
invoked as sudoedit, sudo does not preserve the SUDO_EDITOR, VISUAL or
EDITOR environment variables unless they are present in the env_keep list
or the env_reset option is disabled. The default is /usr/bin/editor.

intercept_type The underlying mechanism used by the intercept and log_subcmds options.
It has the following possible values:

dso Preload a dynamic shared object (shared library) that intercepts
the execve(2), execl(3), execle(3), execlp(3), execv(3),
execvp(3), execvpe(3), and system(3) library functions. A value
of dso is incompatible with sudo's SELinux RBAC support.

trace Use ptrace(2) to intercept the execve(2) system call. This is
only supported on Linux systems where seccomp(2) filtering is
enabled. If the /proc/sys/kernel/seccomp/actions_avail file is
missing or does not contain a “trap” element, setting
intercept_type to trace will have no effect and dso will be used
instead.

The default is to use trace if it is supported by the system and dso if it
is not.

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. 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 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.

log_server_cabundle
The path to a certificate authority bundle file, in PEM format, to use
instead of the system's default certificate authority database when
authenticating the log server. The default is to use the system's default
certificate authority database. This setting has no effect unless
log_servers is set and the remote log server is secured with TLS.

This setting is only supported by version 1.9.0 or higher.

log_server_peer_cert
The path to the sudo client's certificate file, in PEM format. This
setting is required when the remote log server is secured with TLS and
client certificate validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the tls_checkpeer option, which
defaults to false.

This setting is only supported by version 1.9.0 or higher.

log_server_peer_key
The path to the sudo client's private key file, in PEM format. This
setting is required when the remote log server is secured with TLS and
client certificate validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the tls_checkpeer flag, which
defaults to false.

This setting is only supported by version 1.9.0 or higher.

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_askpass_service
On systems that use PAM for authentication, this is the service name used
when the -A option is specified. The default value is either ‘sudo’ or
‘sudo-i’, depending on whether or not the -i option is also specified.
See the description of pam_service for more information.

This setting is only supported by version 1.9.9 or higher.

pam_login_service
On systems that use PAM for authentication, this is the service name used
when the -i option is specified. The default value is ‘sudo-i’. See the
description of pam_service for more information.

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. 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).

kernel The time stamp is stored in the kernel as an attribute of the
terminal device. If no terminal is present, the behavior is the
same as ppid. Negative timestamp_timeout values are not supported
and positive values are limited to a maximum of 60 minutes. This
is currently only supported on OpenBSD.

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:

admin_flag The admin_flag option specifies the path to a file that is created the first
time a user that is a member of the sudo or admin groups runs sudo. Only
available if sudo is configured with the --enable-admin-flag option. The
default value is ~/.sudo_as_admin_successful.

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 enclosed in 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.

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/libexec/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 ("").

On 64-bit systems, if the plugin is present but cannot be loaded, sudoers will
look for a 64-bit version and, if it exists, load that as a fallback. The
exact rules for this vary by system. On Solaris, if the plugin is stored in a
directory ending in “lib”, sudoers will create a fallback path by appending
“/64” to the directory name; /usr/lib/group_plugin.so becomes
/usr/lib/64/group_plugin.so. On Linux, a directory ending in “lib” will be
transformed to “lib64” as the fallback path; /usr/lib/group_plugin.so becomes
/usr/lib64/group_plugin.so. On all other systems, the fallback path is
generated by adding a “64” before the file extension; group_plugin.so becomes
group_plugin64.so.

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.

log_format The event log format. Supported log formats are:

json Logs in JSON format. JSON log entries contain the full user details as
well as the execution environment if the command was allowed. Due to
limitations of the protocol, JSON events sent via syslog may be
truncated.

sudo Traditional sudo-style logs, see EVENT LOGGING for a description of the
log file format.

This setting affects logs sent via syslog(3) as well as the file specified by
the logfile setting, if any. The default value is sudo.

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 (negate to prevent sudo from
sending 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 (negate to prevent sudo from sending
mail). The address should be enclosed in double quotes ("") to protect
against sudo interpreting the ‘@’ sign. Defaults to root.

rlimit_as The maximum size to which the process's address space may grow (in bytes), if
supported by the operating system. See Resource limits for more information.

rlimit_core The largest size core dump file that may be created (in bytes). See Resource
limits for more information. Defaults to 0 (no core dump created).

rlimit_cpu The maximum amount of CPU time that the process may use (in seconds). See
Resource limits for more information.

rlimit_data The maximum size of the data segment for the process (in bytes). See Resource
limits for more information.

rlimit_fsize The largest size file that the process may create (in bytes). See Resource
limits for more information.

rlimit_locks The maximum number of locks that the process may establish, if supported by
the operating system. See Resource limits for more information.

rlimit_memlock
The maximum size that the process may lock in memory (in bytes), if supported
by the operating system. See Resource limits for more information.

rlimit_nofile
The maximum number of files that the process may have open. See Resource
limits for more information.

rlimit_nproc The maximum number of processes that the user may run simultaneously. See
Resource limits for more information.

rlimit_rss The maximum size to which the process's resident set size may grow (in bytes).
See Resource limits for more information.

rlimit_stack The maximum size to which the process's stack may grow (in bytes). See
Resource limits for more information.

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 enclosed in 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.

runchroot If set, sudo will use this value for the root directory when running a
command. The special value “*” will allow the user to specify the root
directory via sudo's -R option. See the Chroot_Spec section for more details.

It is only possible to use runchroot as a command-specific Defaults setting if
the command exists with the same path both inside and outside the chroot jail.
This restriction does not apply to global, host, or user-based Defaults
settings or to a Cmnd_Spec that includes a Chroot_Spec.

This setting is only supported by version 1.9.3 or higher.

runcwd If set, sudo will use this value for the working directory when running a
command. The special value “*” will allow the user to specify the working
directory via sudo's -D option. See the Chdir_Spec section for more details.

This setting is only supported by version 1.9.3 or higher.

secure_path If set, sudo will use this value in place of the user's PATH environment
variable. This option can be used to reset the PATH to a known good value
that contains directories for system administrator commands such as /usr/sbin.

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. Many operating systems will remove potentially dangerous
variables from the environment of any set-user-ID 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.

Preserving the HOME environment variable has security implications since
many programs use it when searching for configuration or data files.
Adding HOME to env_keep may enable a user to run unrestricted commands via
sudo and is strongly discouraged. Users wishing to edit files with sudo
should run sudoedit (or sudo -e) to get their accustomed editor
configuration instead of invoking the editor directly.

log_servers A list of one or more servers to use for remote event and I/O log storage,
separated by white space. Log servers must be running sudo_logsrvd or
another service that implements the protocol described by
sudo_logsrv.proto(5).

Server addresses should be of the form “host[:port][(tls)]”. The host
portion may be a host name, an IPv4 address, or an IPv6 address in square
brackets.

If the optional tls flag is present, the connection will be secured with
Transport Layer Security (TLS) version 1.2 or 1.3. Versions of TLS prior
to 1.2 are not supported.

If a port is specified, it may either be a port number or a well-known
service name as defined by the system service name database. If no port
is specified, port 30343 will be used for plaintext connections and port
30344 will be used for TLS connections.

When log_servers is set, event log data will be logged both locally (see
the syslog and log_file settings) as well as remotely, but I/O log data
will only be logged remotely. If multiple hosts are specified, they will
be attempted in reverse order. If no log servers are available, the user
will not be able to run a command unless either the ignore_iolog_errors
flag (I/O logging enabled) or the ignore_log_errors flag (I/O logging
disabled) is set. Likewise, if the connection to the log server is
interrupted while sudo is running, the command will be terminated unless
the ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.

This setting is only supported by version 1.9.0 or higher.

passprompt_regex A list of POSIX extended regular expressions used to match password
prompts in the terminal output. As an extension, if the regular
expression begins with “(?i)”, it will be matched in a case-insensitive
manner. Each regular expression is limited to 1024 characters. This
option is only used when log_passwords has been disabled. The default
value is “[Pp]assword[: ]*”

This setting is only supported by version 1.9.10 or higher.

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 setting. The argument to
group_plugin should consist of the plugin path, either fully-qualified or relative to the
/usr/libexec/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(3) and getgrid(3). 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).

EVENT LOGGING

sudoers can log events in either JSON or sudo format, this section describes the sudo log
format. Depending on sudoers configuration, sudoers can log events via syslog(3), to a
local log file, or both. 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’. Command
line arguments that contain spaces are enclosed in single quotes (''). This makes it
possible to distinguish multiple command line arguments from a single argument that contains
spaces. 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 ; CHROOT=chroot ; \
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.

chroot The root directory that the command was run in, if one was specified.

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
The -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 open /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, 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, 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(3) 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 LOGGING

When I/O logging is enabled, sudo will runs the command in a pseudo-terminal, logging user
input and/or output, depending on which sudoers flags are enabled. There are five distinct
types of I/O that can be logged, each with a corresponding sudoers flag.

Type Flag Description
terminal input log_ttyin keystrokes entered by the user
terminal output log_ttyout command output displayed to the screen
standard input log_stdin input from a pipe or a file
standard output log_stdout output to a pipe or a file
standard error log_stderr output to a pipe or a file

In addition to flags described the above, the log_input flag and LOG_INPUT command tag set
both log_ttyin and log_stdin. The log_output flag and LOG_OUTPUT command tag set
log_ttyout, log_stdout, and log_stderr.

To capture terminal input and output, sudo run the command in a pseudo-terminal, logging the
input and output before passing it on to the user. To capture the standard input, standard
output or standard error, sudo uses a pipe to interpose itself between the input or output
stream, logging the I/O before passing it to the other end of the pipe.

I/O can be logged either to the local machine or to a remote log server. For local logs,
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. For
remote logs, the log_servers setting is used to specify one or more log servers running
sudo_logsrvd or another server that implements the protocol described by
sudo_logsrv.proto(5).

I/O logging pitfals
When logging standard input, anything sent to the standard input will be consumed,
regardless of whether or not the command run via sudo is actively reading the standard
input. This may have unexpected results when using sudo in a shell script that expects to
process the standard input. For example, given the following shell script:

#!/bin/sh
sudo echo testing
echo done

It will behave as expected when the script is passed to the shell as a an argument:

$ sh test.sh
testing
done

However, if the script is passed to the shell on the standard input, the ‘sudo echo testing’
command will consume the rest of the script. This means that the ‘echo done’ statement is
never executed.

$ sh -s < test.sh
testing

There are several ways to work around this problem:

1. Redirect the standard input from /dev/null when running a command via sudo that does
not need to read the standard input.

sudo echo testing < /dev/null

2. Pass the script to the shell by path name instead of via the standard input.

sh test.sh

3. Disable logging the standard input for commands that do not need to read the standard
input.

Defaults!/bin/echo !log_stdin

Depending on the command, it may not be desirable to log the standard input or standard
output. For example, I/O logging of commands that send or receive large amount of data via
the standard output or standard input such as rsync(1) and tar(1) could fill up the log file
system with superfluous data. It is possible to disable logging of the standard input and
standard output for such commands as follows:

Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync

# Log input and output but omit stdin and stdout when copying files.
Defaults log_input, log_output
Defaults!COPY_CMDS !log_stdin, !log_stdout

However, be aware that using the log_input flag or the LOG_INPUT command tag will also
enable log_stdin. Likewise, the log_ouput flag or the LOG_OUTPUT command tag will enable
log_stdout and log_stderr. Careful ordering of rules may be necessary to achieve the results
that you expect.

I/O log format
For both local and remote I/O logs, each log is stored in a separate directory that contains
the following files:

log A text file containing information about the command. The first line consists of
the following colon-delimited fields: 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, and the number of lines and
columns of the terminal. The second and third lines contain the working directory
the command was run from and the path name of the command itself (with arguments
if present).

log.json A JSON-formatted file containing information about the command. This is similar
to the log file but contains additional information and is easily extensible. The
log.json file will be used by sudoreplay(8) in preference to the log file if it
exists. The file may contain the following elements:

timestamp
A JSON object containing time the command was run. It consists of two
values, seconds and nanoseconds.

columns
The number of columns of the terminal the command ran on, or zero if no
terminal was present.

command
The fully-qualified path of the command that was run.

lines
The number of lines of the terminal the command ran on, or zero if no
terminal was present.

runargv
A JSON array representing the command's argument vector as passed to the
execve(2) system call.

runenv
A JSON array representing the command's environment as passed to the
execve(2) system call.

rungid
The group ID the command ran as. This element is only present when the user
specifies a group on the command line.

rungroup
The name of the group the command ran as. This element is only present when
the user specifies a group on the command line.

runuid
The user ID the command ran as.

runuser
The name of the user the command ran as.

submitcwd
The current working directory at the time sudo was run.

submithost
The name of the host the command was run on.

submituser
The name of the user who ran the command via sudo.

ttyname
The path name of the terminal the user invoked sudo from. If the command
was run in a pseudo-terminal, ttyname will be different from the terminal
the command actually ran in.

timing Timing information used to replay the session. Each line consists of the I/O log
entry type and amount of time since the last entry, followed by type-specific
data. The I/O log entry types and their corresponding type-specific data are:

0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received

ttyin Raw input from the user's terminal, exactly as it was received. This file is only
present if the log_input or log_ttyin flags are set and sudo was run from a
terminal. No post-processing is performed. For manual viewing, you may wish to
convert carriage return characters in the log to line feeds. For example: ‘gunzip
-c ttyin | tr "\r" "\n"’

stdin The standard input when no terminal is present, or input redirected from a pipe or
file. This file is only present if the log_input or log_stdin flags are set and
the standard input is not connected to a terminal.

ttyout Output from the pseudo-terminal (what the command writes to the screen).
Terminal-specific post-processing is performed before the data is logged. This
means that, for example, line feeds are usually converted to line feed/carriage
return pairs and tabs may be expanded to spaces. This file is only present if the
log_output or log_ttyout flags are set and sudo was run from a terminal.

stdout The standard output when no terminal is present, or output redirected to a pipe or
file. This file is only present if the log_output or log_stdout flags are set and
the standard output is not connected to a terminal.

stderr The standard error when no terminal is present, or output redirected to a pipe or
file. This file is only present if the log_output or log_stderr flags are set and
the standard error is not connected to a terminal.

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.

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. When logging
input, consider disabling the log_passwords flag.

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.  Other programs use HOME to locate 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      WEBADMIN = 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 = primary, 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 and for commands to be run with the target user's home
     directory as the working directory.  We don't want to subject the full time staff to the
     sudo lecture and we want to allow them to run commands in a chroot(2) “sandbox” via the -R
     option.  User millert need not provide a password and we don't want to reset the LOGNAME or
     USER 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).  This will not effectively constrain users with sudo ALL privileges.

     # Override built-in defaults
     Defaults                syslog=auth,runcwd=~
     Defaults>root           !set_logname
     Defaults:FULLTIMERS     !lecture,runchroot=*
     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/.  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.  On systems with GNU getopt(3), 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
     (primary, 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.

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

     On the host www, any user in the WEBADMIN 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.

Another potential issue is that when sudo executes the command, it must use the command or
path specified by the user instead of a path listed in the sudoers file. This may lead to a
time of check versus time of use race condition.

Wildcards in command arguments
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. A safer alternative is to use a regular expression
for matching command line arguments. The above example can be rewritten as a regular
expression:

%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$

The regular expression will only match a single file with a name that begins with
/var/log/messages and does not include any white space in the name. It is often better to
do command line processing outside of the sudoers file in a scripting language for anything
non-trivial.

Regular expressions in command names
Using a regular expression to match a command name has the same security implications as
using the fast_glob option:

• It is not possible to reliably negate commands when the path name is a regular
expression.

• When sudo executes the command, it must use the command or path specified by the user
instead of a path listed in the sudoers file. This may lead to a time of check versus
time of use race condition.

These issues do not apply to rules where only the command line options are matched using a
regular expression.

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 four 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.

intercept On most systems, sudo's intercept functionality can be used to transparently
intercept an attempt to run a new command, allow or deny it based on sudoers
rules, and log the result. For example, this can be used to restrict the
commands run from within a privileged shell or editor.

There are two underlying mechanisms that may be used to implement intercept mode:
dso and trace. The intercept_type setting can be used to select between them.

The first mechanism, dso, overrides the standard C library functions that are
used to execute a command. It does this by setting an environment variable
(usually LD_PRELOAD) to the path of a dynamic shared object, or shared library,
containing custom versions of the execve(2), execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), and system(3) library functions that connect
back to sudo for a policy decision. Note, however, that this applies only to
dynamically-linked executables. It is not possible to intercept commands for
statically-linked executables or executables that run under binary emulation this
way. Because most dynamic loaders ignore LD_PRELOAD (or the equivalent) when
running set-user-ID and set-group-ID programs, sudoers will not permit such
programs to be run in intercept mode by default. The dso mechanism is
incompatible with sudo's SELinux RBAC support (but see below). SELinux disables
LD_PRELOAD by default and interferes with file descriptor inheritance, which sudo
relies on.

The second mechanism, trace, is available on Linux systems that support
seccomp(2) filtering. It uses ptrace(2) and seccomp(2) to intercept the
execve(2) system call instead of pre-loading a dynamic shared object. Both
static and dynamic executables are supported and it is compatible with sudo's
SELinux RBAC mode. Functions utilizing the execveat(2) system call, such as
fexecve(3), are not currently intercepted.

The intercept feature is known to work on Solaris, *BSD, Linux, 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 or an equivalent. It is not possible
to intercept shell built-in commands or restrict the ability to read or write
sensitive files from within a shell.

To enable intercept mode on a per-command basis, use the INTERCEPT tag as
documented in the User Specification section above. Here is that example again:

chuck research = INTERCEPT: ALL

This allows user chuck to run any command on the machine “research” in intercept
mode. Any commands run via shell escapes will be validated and logged by sudo.
If you are unsure whether or not your system is capable of supporting intercept,
you can always just try it out and check whether or not external commands run via
a shell are logged when intercept is enabled.

There is an inherent race condition between when a command is checked against
sudoers rules and when it is actually executed. If a user is allowed to run
arbitrary commands, they may be able to change the execve(2) arguments in the
program after the sudoers policy check has completed but before the new command
is executed. Starting with version 1.9.12, the trace method will verify that the
command and its arguments have not changed after execve(2) has completed but
before execution of the new program has had a chance to run. This is not the
case with the dso method. See the description of the intercept_verify setting
for more information.

log There are two separate but related ways to log additional commands. The first is
to enable I/O logging using the log_output flag. This will log the command's
output but will not create an event log entry when the additional command is run.
The second is to enable the log_subcmds flag in sudoers which will create an
event log entry every time a new command is run. If I/O logging is also enabled,
the log entry will include a time offset into the I/O log to indicate when the
command was run. This offset can be passed to the sudoreplay(8) utility to
replay the I/O log at the exact moment when the command was run. The log_subcmds
flag uses the same mechanism as intercept (see above) and has the same
limitations.

noexec sudo's noexec functionality can be used to prevent a program run by sudo from
executing any other programs. On most systems, it uses the same LD_PRELOAD
mechanism as intercept (see above) and thus the same caveats apply. The noexec
functionality is capable of blocking execution of commands run via the execve(2),
execl(3), execle(3), execlp(3), exect(3), execv(3), execveat(3), execvP(3),
execvp(3), execvpe(3), fexecve(3), popen(3), posix_spawn(3), posix_spawnp(3),
system(3), and wordexp(3) functions. On Linux, a seccomp(2) filter is used to
implement noexec. On Solaris 10 and higher, noexec uses Solaris privileges
instead of the LD_PRELOAD environment variable.

To enable noexec for a command, use the NOEXEC tag as documented in the User
Specification section above. Here is that example again:

aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi

This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled.
This will prevent those two commands from executing other commands (such as a
shell). If you are unsure whether or not your system is capable of supporting
noexec you can always just try it out and check whether shell escapes work when
noexec is enabled.

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 on any machine:

operator ALL = 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
/run or /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.

If the timestamp_type option is set to “tty”, the time stamp record includes the device
number of the terminal the user authenticated with. This provides per-terminal granularity
but time stamp records may still outlive the user's session.

Unless the timestamp_type option is set to “global”, 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. On systems where a process's start
time can be queried, the start time of the session leader is recorded in the time stamp
record. If no terminal is present or the timestamp_type option is set to “ppid”, the start
time of the parent process is used instead. In most cases this will prevent a time stamp
record from being re-used without the user entering a password when logging out and back in
again.

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-terminal related code

     rbtree    redblack tree internals

     sssd      SSSD-based sudoers

     util      utility functions

     For example:

     Debug sudoers.so /var/log/sudoers_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.md file in the sudo distribution
     (https://www.sudo.ws/about/contributors/) for an exhaustive list of people who have
     contributed to sudo.

CAVEATS

     The sudoers file should always be edited by the visudo utility which locks the file and
     checks for syntax errors.  If sudoers contains syntax errors, sudo may refuse to run, which
     is a serious problem if sudo is your only method of obtaining superuser privileges.  Recent
     versions of sudoers will attempt to recover after a syntax error by ignoring the rest of the
     line after encountering an error.  Older versions of sudo will not run if sudoers contains a
     syntax error.

     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 believe you have found a bug in sudo, you can 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.md file distributed with sudo or
     https://www.sudo.ws/about/license/ for complete details.

NAME

DESCRIPTION

SUDOERS FILE FORMAT

SUDOERS OPTIONS

GROUP PROVIDER PLUGINS

EVENT LOGGING

I/O LOGGING

FILES

EXAMPLES

SECURITY NOTES

DEBUGGING

SEE ALSO

AUTHORS

CAVEATS

BUGS

SUPPORT

DISCLAIMER