sudoers • man page

sudoers (5)

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 Copyright (c) 1994-1996, 1998-2005, 2007-2017
	Todd C. Miller <Todd.Miller@courtesan.com>

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(The comments found at the beginning of the groff file "man5/sudoers.5".)

NAME

sudoers - default sudo security policy plugin

DESCRIPTION

The ~/.ssh/config 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 Sx SUDOERS FILE FORMAT section. For information on storing sudoers policy information in LDAP, please see sudoers.ldap5.

Configuring sudo.conf for sudoers

sudo consults the sudo.conf5 file to determine which policy and and I/O logging plugins to load. If no sudo.conf5 file is present, or if it contains no Plugin lines, ~/.ssh/config will be used for policy decisions and I/O logging. To explicitly configure sudo.conf5 to use the ~/.ssh/config plugin, the following configuration can be used.

Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so

Starting with sudo 1.8.5, it is possible to specify optional arguments to the ~/.ssh/config plugin in the sudo.conf5 file. These arguments, if present, should be listed after the path to the plugin (i.e. after sudoers.so ) Multiple arguments may be specified, separated by white space. For example:

Plugin sudoers_policy sudoers.so sudoers_mode=0400

The following plugin arguments are supported:

ldap_conf=pathname: The ldap_conf argument can be used to override the default path to the ldap.conf file.
ldap_secret=pathname: The ldap_secret argument can be used to override the default path to the ldap.secret file.
sudoers_file=pathname: The sudoers_file argument can be used to override the default path to the sudoers file.
sudoers_uid=uid: The sudoers_uid argument can be used to override the default owner of the sudoers file. It should be specified as a numeric user ID.
sudoers_gid=gid: The sudoers_gid argument can be used to override the default group of the sudoers file. It must be specified as a numeric group ID (not a group name).
sudoers_mode=mode: The sudoers_mode argument can be used to override the default file mode for the sudoers file. It should be specified as an octal value.

For more information on configuring sudo.conf5, please refer to its manual.

User Authentication

The sudoers security policy requires that most users authenticate themselves before they can use sudo A password is not required if the invoking user is root, if the target user is the same as the invoking user, or if the policy has disabled authentication for the user or command. Unlike su(1), when sudoers requires authentication, it validates the invoking user's credentials, not the target user's (or root's) credentials. This can be changed via the rootpw targetpw and runaspw flags, described later.

If a user who is not listed in the policy tries to run a command via sudo mail is sent to the proper authorities. The address used for such mail is configurable via the mailto Defaults entry (described later) and defaults to root

Note that no mail will be sent if an unauthorized user tries to run sudo with the -l or -v option unless there is an authentication error and either the mail_always or mail_badpass flags are enabled. This allows users to determine for themselves whether or not they are allowed to use sudo All attempts to run sudo (successful or not) will be logged, regardless of whether or not mail is sent.

If sudo is run by root and the SUDO_USER environment variable is set, the sudoers policy will use this value to determine who the actual user is. This can be used by a user to log commands through sudo even when a root shell has been invoked. It also allows the -e option to remain useful even when invoked via a sudo-run script or program. Note, however, that the sudoers file lookup is still done for root, not the user specified by SUDO_USER

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

Logging

sudoers can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default, sudoers will log via syslog(3) but this is changeable via the syslog and logfile Defaults settings. See Sx LOG FORMAT for a description of the log file format.

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

Command environment

Since environment variables can influence program behavior, sudoers provides a means to restrict which variables from the user's environment are inherited by the command to be run. There are two distinct ways sudoers can deal with environment variables.

By default, the env_reset option is enabled. This causes commands to be executed with a new, minimal environment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of the /etc/environment file. The new environment contains the TERM PATH HOME MAIL SHELL LOGNAME USER USERNAME and SUDO_* variables in addition to variables from the invoking process permitted by the env_check and env_keep options. This is effectively a whitelist for environment variables. Environment variables with a value beginning with () are removed unless both the name and value parts are matched by env_keep or env_check as they will be interpreted as functions by older versions of the bash shell. Prior to version 1.8.11, such variables were always removed.

If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave like a blacklist. Environment variables with a value beginning with () are always removed, even if they do not match one of the blacklists. Since it is not possible to blacklist all potentially dangerous environment variables, use of the default env_reset behavior is encouraged.

By default, environment variables are matched by name. However, if the pattern includes an equal sign (`=' ) both the variables name and value must match. For example, an old-style (pre-shellshock) bash shell function could be matched as follows:

env_keep += "my_func=()*"

Without the ``=()* '' suffix, this would not match, as old-style bash shell functions are not preserved by default.

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

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

Note that the dynamic linker on most operating systems will remove variables that can control dynamic linking from the environment of setuid executables, including sudo Depending on the operating system this may include _RLD* DYLD_* LD_* LDR_* LIBPATH SHLIB_PATH and others. These type of variables are removed from the environment before sudo even begins execution and, as such, it is not possible for sudo to preserve them.

As a special case, if sudo 's -i option (initial login) is specified, sudoers will initialize the environment regardless of the value of env_reset The DISPLAY PATH and TERM variables remain unchanged; HOME MAIL SHELL USER and LOGNAME are set based on the target user. On AIX (and Linux systems without PAM), the contents of /etc/environment are also included. All other environment variables are removed.

Finally, if the env_file option is defined, any variables present in that file will be set to their specified values as long as they would not conflict with an existing environment variable.

SUDOERS FILE FORMAT

The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).

When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).

The sudoers file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.

Quick guide to EBNF

EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of production rules E.g.,

symbol ::= definition | alternate1 | alternate2 ...

Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with ``wildcard'' characters, which have different meanings.

?: Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all.
*: Means that the preceding symbol (or group of symbols) may appear zero or more times.
+: Means that the preceding symbol (or group of symbols) may appear one or more times.

Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).

Aliases

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

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

User_Alias ::= NAME '=' User_List

Runas_Alias ::= NAME '=' Runas_List

Host_Alias ::= NAME '=' Host_List

Cmnd_Alias ::= NAME '=' Cmnd_List

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

Each alias definition is of the form

Alias_Type NAME = item1, item2, ...

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

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

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

The definitions of what constitutes a valid alias member follow.

User_List ::= User |
              User ',' User_List

User ::= '!'* user name |
         '!'* #uid |
         '!'* %group |
         '!'* %#gid |
         '!'* +netgroup |
         '!'* %:nonunix_group |
         '!'* %:#nonunix_gid |
         '!'* User_Alias

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_Alias es. Each list item may be prefixed with zero or more `!' operators. An odd number of `!' operators negate the value of the item; an even number just cancel each other out. User netgroups are matched using the user and domain members only; the host member is not used when matching.

A user name uid group gid netgroup nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g. \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.

The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin. For instance, the QAS AD plugin supports the following formats:

Group in the same domain: "%:Group Name"
Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"

See Sx GROUP PROVIDER PLUGINS for more information.

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

Runas_List ::= Runas_Member |
               Runas_Member ',' Runas_List

Runas_Member ::= '!'* user name |
                 '!'* #uid |
                 '!'* %group |
                 '!'* %#gid |
                 '!'* %:nonunix_group |
                 '!'* %:#nonunix_gid |
                 '!'* +netgroup |
                 '!'* Runas_Alias

A Runas_List is similar to a User_List except that instead of User_Alias es it can contain Runas_Alias es Note that user names and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are considered to be distinct. If you wish to match all user names with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given).

Host_List ::= Host |
              Host ',' Host_List

Host ::= '!'* host name |
         '!'* ip_addr |
         '!'* network(/netmask)? |
         '!'* +netgroup |
         '!'* Host_Alias

A Host_List is made up of one or more host names, IP addresses, network numbers, netgroups (prefixed with `+' ) and other aliases. Again, the value of an item may be negated with the `!' operator. Host netgroups are matched using the host (both qualified and unqualified) and domain members only; the user member is not used when matching. If you specify a network number without a netmask, sudo will query each of the local host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces, will use the netmask of that interface. The netmask may be specified either in standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g. 24 or 64). A host name may include shell-style wildcards (see the Sx Wildcards section below), but unless the host name command on your machine returns the fully qualified host name, you'll need to use the fqdn option for wildcards to be useful. Note that sudo only inspects actual network interfaces; this means that IP address 127.0.0.1 (localhost) will never match. Also, the host name ``localhost'' will only match if that is the actual host name, which is usually only the case for non-networked systems.

digest ::= [A-Fa-f0-9]+ |
           [[A-Za-z0-9+/=]+

Digest_Spec ::= "sha224" ':' digest |
                "sha256" ':' digest |
                "sha384" ':' digest |
                "sha512" ':' digest

Cmnd_List ::= Cmnd |
              Cmnd ',' Cmnd_List

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

Cmnd ::= Digest_Spec? '!'* command name |
         '!'* directory |
         '!'* "sudoedit" |
         '!'* Cmnd_Alias

A Cmnd_List is a list of one or more command names, directories, and other aliases. A command name is a fully qualified file name which may include shell-style wildcards (see the Sx Wildcards section below). A simple file name allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify to indicate that the command may only be run without command line arguments. A directory is a fully qualified path name ending in a `/' When you specify a directory in a Cmnd_List the user will be able to run any file within that directory (but not in any sub-directories therein).

If a Cmnd has associated command line arguments, then the arguments in the Cmnd must match exactly those given by the user on the command line (or match the wildcards if there are any). Note that the following characters must be escaped with a `\' if they are used in command arguments: `,' , `:' , `=' , `\' The built-in command ``sudoedit '' is used to permit a user to run sudo with the -e option (or as sudoedit ) It may take command line arguments just as a normal command does. Note that ``sudoedit '' is a command built into sudo itself and must be specified in the sudoers file without a leading path.

If a command name is prefixed with a Digest_Spec the command will only match successfully if it can be verified using the specified SHA-2 digest. The following digest formats are supported: sha224, sha256, sha384 and sha512. The string may be specified in either hex or base64 format (base64 is more compact). There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.

For example, using openssl:

$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25

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

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

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

Command digests are only supported by version 1.8.7 or higher.

Defaults

Certain configuration options may be changed from their default values at run-time via one or more Default_Entry lines. These may affect all users on any host, all users on a specific host, a specific user, a specific command, or commands being run as a specific user. Note that per-command entries may not include command line arguments. If you need to specify arguments, define a Cmnd_Alias and reference that instead.

Default_Type ::= 'Defaults' |
                 'Defaults' '@' Host_List |
                 'Defaults' ':' User_List |
                 'Defaults' '!' Cmnd_List |
                 'Defaults' '>' Runas_List

Default_Entry ::= Default_Type Parameter_List

Parameter_List ::= Parameter |
                   Parameter ',' Parameter_List

Parameter ::= Parameter '=' Value |
              Parameter '+=' Value |
              Parameter '-=' Value |
              '!'* Parameter

Parameters may be flags integer values, strings or lists Flags are implicitly boolean and can be turned off via the `!' operator. Some integer, string and list parameters may also be used in a boolean context to disable them. Values may be enclosed in double quotes () when they contain multiple words. Special characters may be escaped with a backslash (`\' )

Lists have two additional assignment operators, += and -= These operators are used to add to and delete from a list respectively. It is not an error to use the -= operator to remove an element that does not exist in a list.

Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas Defaults and finally command defaults.

See Sx SUDOERS OPTIONS for a list of supported Defaults parameters.

User specification

User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
              (':' Host_List '=' Cmnd_Spec_List)*

Cmnd_Spec_List ::= Cmnd_Spec |
                   Cmnd_Spec ',' Cmnd_Spec_List

Cmnd_Spec ::= Runas_Spec? SELinux_Spec? Tag_Spec* Cmnd

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

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

Tag_Spec ::= ('EXEC:' | 'NOEXEC:' | 'FOLLOW:' | 'NOFOLLOW' |
              'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' |
              'NOLOG_OUTPUT:' | 'MAIL:' | 'NOMAIL:' | 'PASSWD:' |
              'NOPASSWD:' | 'SETENV:' | 'NOSETENV:')

A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root but this can be changed on a per-command basis.

The basic structure of a user specification is ``who where = (as_whom) what'' Let's break that down into its constituent parts:

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_List s (as defined above) separated by a colon (`:' ) and enclosed in a set of parentheses. The first Runas_List indicates which users the command may be run as via sudo 's -u option. The second defines a list of groups that can be specified via sudo 's -g option. If both Runas_List s are specified, the command may be run with any combination of users and groups listed in their respective Runas_List s. If only the first is specified, the command may be run as any user in the list but no -g option may be specified. If the first 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_List s are empty, the command may only be run as the invoking user. If no Runas_Spec is specified the command may be run as root and no group may be specified.

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

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

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

$ sudo -u operator /bin/ls

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

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

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

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

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

Note that while the group portion of the Runas_Spec permits the user to run as command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:

$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls

In the following example, user tcm may run commands that access a modem device file with the dialer group.

tcm     boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
        /usr/local/bin/minicom

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

$ sudo -g dialer /usr/bin/cu

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

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

user alan may run any command as either user root or bin, optionally setting the group to operator or system.

SELinux_Spec

On systems with SELinux support, sudoers file entries may optionally have an SELinux role and/or type associated with a command. If a role or type is specified with the command it will override any default values specified in sudoers A role or type specified on the command line, however, will supersede the values in sudoers

Tag_Spec

A command may have zero or more tags associated with it. There are ten possible tag values: EXEC NOEXEC FOLLOW NOFOLLOW LOG_INPUT NOLOG_INPUT LOG_OUTPUT NOLOG_OUTPUT MAIL NOMAIL PASSWD NOPASSWD SETENV and NOSETENV Once a tag is set on a Cmnd subsequent Cmnd s 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 Sx Preventing shell escapes section below for more details on how NOEXEC works and whether or not it will work on your system.

FOLLOW and NOFOLLOW

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

LOG_INPUT and NOLOG_INPUT

These tags override the value of the log_input option on a per-command basis. For more information, see the description of log_input in the Sx SUDOERS OPTIONS section below.

LOG_OUTPUT and NOLOG_OUTPUT

These tags override the value of the log_output option on a per-command basis. For more information, see the description of log_output in the Sx SUDOERS OPTIONS section below.

MAIL and NOMAIL

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

PASSWD and NOPASSWD

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

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

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

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

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

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

SETENV and NOSETENV

These tags override the value of the setenv option on a per-command basis. Note that if SETENV has been set for a command, the user may disable the env_reset option from the command line via the -E option. Additionally, environment variables set on the command line are not subject to the restrictions imposed by env_check env_delete or env_keep As such, only trusted users should be allowed to set variables in this manner. If the command matched is ALL the SETENV tag is implied for that command; this default may be overridden by use of the NOSETENV tag.

Wildcards

sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names and command line arguments in the sudoers file. Wildcard matching is done via the glob(3) and fnmatch(3) functions as specified by St -p1003.1 .

*: 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 `]'

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

Character classes may be used if your system's glob(3) and fnmatch(3) functions support them. However, because the `:' character has special meaning in sudoers it must be escaped. For example:

/bin/ls [[\:alpha\:]]*

Would match any file name beginning with a letter.

Note that a forward slash (`/' ) will not be matched by wildcards used in the file name portion of the command. This is to make a path like:

/usr/bin/*

match /usr/bin/who but not /usr/bin/X11/xterm

When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.

Bf -symbolic Wildcards in command line arguments should be used with care. Ef
Command line arguments are matched as a single, concatenated string. This mean a wildcard character such as `?' or `*' will match across word boundaries, which may be unexpected. For example, while a sudoers entry like:

%operator ALL = /bin/cat /var/log/messages*

will allow command like:

$ sudo cat /var/log/messages.1

It will also allow:

$ sudo cat /var/log/messages /etc/shadow

which is probably not what was intended. In most cases it is better to do command line processing outside of the sudoers file in a scripting language.

Exceptions to wildcard rules

The following exceptions apply to the above rules:

: If the empty string is the only command line argument in the sudoers file entry it means that command is not allowed to be run with any arguments.
sudoedit: Command line arguments to the sudoedit built-in command should always be path names, so a forward slash (`/' ) will not be matched by a wildcard.

Including other files from within sudoers

It is possible to include other sudoers files from within the sudoers file currently being parsed using the #include and #includedir directives.

This can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers file will be /etc/sudoers and the per-machine one will be /etc/sudoers.local To include /etc/sudoers.local from within /etc/sudoers we would use the following line in /etc/sudoers

#include /etc/sudoers.local

When sudo reaches this line it will suspend processing of the current file (/etc/sudoers ) and switch to /etc/sudoers.local Upon reaching the end of /etc/sudoers.local the rest of /etc/sudoers will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops.

If the path to the include file is not fully-qualified (does not begin with a `/' , it must be located in the same directory as the sudoers file it was included from. For example, if /etc/sudoers contains the line:

#include sudoers.local

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

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

#include /etc/sudoers.%h

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

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

#includedir /etc/sudoers.d

sudo will read each file in /etc/sudoers.d skipping file names that end in `~' or contain a `.' character to avoid causing problems with package manager or editor temporary/backup files. Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second Using a consistent number of leading zeroes in the file names can be used to avoid such problems.

Note that unlike files included via #include visudo will not edit the files in a #includedir directory unless one of them contains a syntax error. It is still possible to run visudo with the -f flag to edit the files directly, but this will not catch the redefinition of an alias that is also present in a different file.

Other special characters and reserved words

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

The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias User_Alias Runas_Alias or Host_Alias You should not try to define your own alias called ALL as the built-in alias will be used in preference to your own. Please note that using ALL can be dangerous since in a command context, it allows the user to run any command on the system.

An exclamation point (`!' ) can be used as a logical not operator in a list or alias as well as in front of a Cmnd This allows one to exclude certain values. For the `!' operator to be effective, there must be something for it to exclude. For example, to match all users except for root one would use:

ALL,!root

If the ALL is omitted, as in:

!root

it would explicitly deny root but not match any other users. This is different from a true ``negation'' operator.

Note, however, that using a `!' in conjunction with the built-in ALL alias to allow a user to run ``all but a few'' commands rarely works as intended (see Sx 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 Po `=' , `:' , `(' , `)' Pc is optional.

The following characters must be escaped with a backslash (`\' ) when used as part of a word (e.g. a user name or host name): `!' , `=' , `:' , `,' , `(' , `)' , `\'

SUDOERS OPTIONS

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

Boolean Flags

always_query_group_plugin

If a group_plugin is configured, use it to resolve groups of the form %group as long as there is not also a system group of the same name. Normally, only groups of the form %:group are passed to the group_plugin This flag is off by default.

always_set_home

If enabled, sudo will set the HOME environment variable to the home directory of the target user (which is root unless the -u option is used). This effectively means that the -H option is always implied. Note that by default, HOME will be set to the home directory of the target user when the env_reset option is enabled, so always_set_home only has an effect for configurations where either env_reset is disabled or HOME is present in the env_keep list. This flag is off by default.

authenticate

If set, users must authenticate themselves via a password (or other means of authentication) before they may run commands. This default may be overridden via the PASSWD and NOPASSWD tags. This flag is on by default.

closefrom_override

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

compress_io

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

exec_background

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

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

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

env_editor

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

env_reset

If set, sudo will run the command in a minimal environment containing the TERM PATH HOME MAIL SHELL LOGNAME USER USERNAME and SUDO_* variables. Any variables in the caller's environment that match the env_keep and env_check lists are then added, followed by any variables present in the file specified by the env_file option (if any). The contents of the env_keep and env_check lists, as modified by global Defaults parameters in sudoers are displayed when sudo is run by root with the -V option. If the secure_path option is set, its value will be used for the PATH environment variable. This flag is on by default.

fast_glob

Normally, sudo uses the glob(3) function to do shell-style globbing when matching path names. However, since it accesses the file system, glob(3) can take a long time to complete for some patterns, especially when the pattern references a network file system that is mounted on demand (auto mounted). The fast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do its matching. The disadvantage of fast_glob is that it is unable to match relative path names such as ./ls or ../bin/ls This has security implications when path names that include globbing characters are used with the negation operator, `!' , as such rules can be trivially bypassed. As such, this option should not be used when the sudoers file contains rules that contain negated path names which include globbing characters. This flag is off by default.

fqdn

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

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

192.168.1.1 xyzzy.sudo.ws xyzzy

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

Beware that when using DNS for host name resolution, turning on fqdn requires ~/.ssh/config to make DNS lookups which renders sudo unusable if DNS stops working (for example if the machine is disconnected from the network). Also note that just like with the hosts file, you must use the ``canonical'' name as DNS knows it. That is, you may not use a host alias Po CNAME entry Pc 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_dot

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

ignore_local_sudoers

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

insults

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

log_host

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

log_input

If set, sudo will run the command in a pseudo-tty and log all user input. If the standard input is not connected to the user's tty, due to I/O redirection or because the command is part of a pipeline, that input is also captured and stored in a separate log file. For more information, see the Sx I/O LOG FILES section. This flag is off by default.

log_output

If set, sudo will run the command in a pseudo-tty and log all output that is sent to the screen, similar to the script(1) command. For more information, see the Sx I/O LOG FILES section. This flag is off by default.

log_year

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

long_otp_prompt

When validating with a One Time Password (OTP) scheme such as S/Key or OPIE a two-line prompt is used to make it easier to cut and paste the challenge to a local window. It's not as pretty as the default but some people find it more convenient. This flag is off by default.

mail_all_cmnds

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

mail_always

Send mail to the mailto user every time a user runs sudo This flag is off by default.

mail_badpass

Send mail to the mailto user if the user running sudo does not enter the correct password. If the command the user is attempting to run is not permitted by sudoers and one of the mail_all_cmnds mail_always mail_no_host mail_no_perms or mail_no_user flags are set, this flag will have no effect. This flag is off by default.

mail_no_host

If set, mail will be sent to the mailto user if the invoking user exists in the sudoers file, but is not allowed to run commands on the current host. This flag is off by default.

mail_no_perms

If set, mail will be sent to the mailto user if the invoking user is allowed to use sudo but the command they are trying is not listed in their sudoers file entry or is explicitly denied. This flag is off by default.

mail_no_user

If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file. This flag is on by default.

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 Sx Preventing shell escapes section at the end of this manual. This flag is off by default.

pam_session

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

This setting is only supported by version 1.8.7 or higher.

pam_setcred

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

This setting is only supported by version 1.8.8 or higher.

passprompt_override

The password prompt specified by passprompt will normally only be used if the password prompt provided by systems such as PAM matches the string ``Password:'' If passprompt_override is set, passprompt will always be used. This flag is off by default.

path_info

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

preserve_groups

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

pwfeedback

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

requiretty

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

root_sudo

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

rootpw

If set, sudo will prompt for the root password instead of the password of the invoking user when running a command or editing a file. This flag is off by default.

runaspw

If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to root instead of the password of the invoking user when running a command or editing a file. This flag is off by default.

set_home

If enabled and sudo is invoked with the -s option the HOME environment variable will be set to the home directory of the target user (which is root unless the -u option is used). This effectively makes the -s option imply -H Note that HOME is already set when the env_reset option is enabled, so set_home is only effective for configurations where either env_reset is disabled or HOME is present in the env_keep list. This flag is off by default.

set_logname

Normally, sudo will set the LOGNAME USER and USERNAME environment variables to the name of the target user (usually root unless the -u option is given). However, since some programs (including the RCS revision control system) use LOGNAME to determine the real identity of the user, it may be desirable to change this behavior. This can be done by negating the set_logname option. Note that set_logname will have no effect if the env_reset option has not been disabled and the env_keep list contains LOGNAME USER or USERNAME This flag is on by default.

set_utmp

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

setenv

Allow the user to disable the env_reset option from the command line via the -E option. Additionally, environment variables set via the command line are not subject to the restrictions imposed by env_check env_delete or env_keep As such, only trusted users should be allowed to set variables in this manner. This flag is off by default.

shell_noargs

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

stay_setuid

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

sudoedit_checkdir

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

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

sudoedit_follow

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

This setting is only supported by version 1.8.15 or higher.

targetpw

If set, sudo will prompt for the password of the user specified by the -u option (defaults to root instead of the password of the invoking user when running a command or editing a file. Note that this flag precludes the use of a uid not listed in the passwd database as an argument to the -u option. This flag is off by default.

tty_tickets

If set, users must authenticate on a per-tty basis. With this flag enabled, sudo will use a separate record in the time stamp file for each tty. If disabled, a single record is used for all login sessions. This flag is on by default.

umask_override

If set, sudo will set the umask as specified in the sudoers file without modification. This makes it possible to specify a umask in the sudoers file that is more permissive than the user's own umask and matches historical behavior. If umask_override is not set, sudo will set the umask to be the union of the user's umask and what is specified in sudoers This flag is off by default.

use_netgroups

If set, netgroups (prefixed with `+' ) , may be used in place of a user or host. For LDAP-based sudoers, netgroup support requires an expensive substring match on the server unless the NETGROUP_BASE directive is present in the /etc/ldap.conf file. If netgroups are not needed, this option can be disabled to reduce the load on the LDAP server. This flag is on by default.

use_pty

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

utmp_runas

If set, sudo will store the name of the runas user when updating the utmp (or utmpx) file. By default, sudo stores the name of the invoking user. This flag is off by default.

visiblepw

By default, sudo will refuse to run if the user must enter a password but it is not possible to disable echo on the terminal. If the visiblepw flag is set, sudo will prompt for a password even when it would be visible on the screen. This makes it possible to run things like ``ssh somehost sudo ls '' since by default, ssh(1) does not allocate a tty when running a command. This flag is off by default.

Integers

closefrom

Before it executes a command, sudo will close all open file descriptors other than standard input, standard output and standard error (ie: file descriptors 0-2). The closefrom option can be used to specify a different file descriptor at which to start closing. The default is 3

maxseq

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

Once the local sequence number reaches the value of maxseq it will ``roll over'' to zero, after which ~/.ssh/config 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

Integers that can be used in a boolean context

loglinelen: Number of characters per line for the file log. This value is used to decide when to wrap lines for nicer log files. This has no effect on the syslog log file, only the file log. The default is 80 (use 0 or negate the option to disable word wrap).
passwd_timeout: Number of minutes before the sudo password prompt times out, or 0 for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example 2.5 The default is 0
timestamp_timeout: Number of minutes that can elapse before sudo will ask for a passwd again. The timeout may include a fractional component if minute granularity is insufficient, for example 2.5 The default is 15 Set this to 0 to always prompt for a password. If set to a value less than 0 the user's time stamp will never expire. This can be used to allow users to create or delete their own time stamps via ``sudo -v '' and ``sudo -k '' respectively.
umask: Umask to use when running the command. Negate this option or set it to 0777 to preserve the user's umask. The actual umask that is used will be the union of the user's umask and the value of the umask option, which defaults to 0022 This guarantees that sudo never lowers the umask when running a command. Note: on systems that use PAM, the default PAM configuration may specify its own umask which will override the value set in sudoers

Strings

badpass_message

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

editor

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

iolog_dir

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

The following percent (`%' ) escape sequences are supported:

%{seq}: expanded to a monotonically increasing base-36 sequence number, such as 0100A5, where every two digits are used to form a new directory, e.g. 01/00/A5
%{user}: expanded to the invoking user's login name
%{group}: expanded to the name of the invoking user's real group ID
%{runas_user}: expanded to the login name of the user the command will be run as (e.g. root)
%{runas_group}: expanded to the group name of the user the command will be run as (e.g. wheel)
%{hostname}: expanded to the local host name without the domain name
%{command}: expanded to the base name of the command being run

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

To include a literal `%' character, the string `%%' should be used.

iolog_file

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

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

In addition to the escape sequences, path names that end in six or more X s will have the X s 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 X s

lecture_status_dir

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

mailsub

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

noexec_file

As of sudo version 1.8.1 this option is no longer supported. The path to the noexec file should now be set in the sudo.conf5 file.

pam_login_service

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

This setting is only supported by version 1.8.8 or higher.

pam_service

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

This setting is only supported by version 1.8.8 or higher.

passprompt

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

%H: expanded to the local host name including the domain name (only if the machine's host name is fully qualified or the fqdn option is set)
%h: expanded to the local host name without the domain name
%p: expanded to the user whose password is being asked for (respects the rootpw targetpw and runaspw flags in sudoers
%U: expanded to the login name of the user the command will be run as (defaults to root)
%u: expanded to the invoking user's login name
%%: two consecutive % characters are collapsed into a single % character

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

syslog_badpri

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

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

syslog_goodpri

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

See syslog_badpri for the list of supported syslog priorities.

sudoers_locale

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

timestampdir

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

timestampowner

The owner of the lecture status directory, time stamp directory and all files stored therein. The default is root

type

The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in the sudoers file or via command line options. This option is only available when sudo is built with SELinux support.

Strings that can be used in a boolean context

env_file

The env_file option specifies the fully qualified path to a file containing variables to be set in the environment of the program being run. Entries in this file should either be of the form ``VARIABLE=value '' or ``export VARIABLE=value '' The value may optionally be surrounded by single or double quotes. Variables in this file are subject to other sudo environment settings such as env_keep and env_check

exempt_group

Users in this group are exempt from password and PATH requirements. The group name specified should not include a % prefix. This is not set by default.

group_plugin

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

For more information see GROUPPROVIDERPLUGINS.

lecture

This option controls when a short lecture will be printed along with the password prompt. It has the following possible values:

always: Always lecture the user.
never: Never lecture the user.
once: Only lecture the user the first time they run sudo

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

lecture_file

Path to a file containing an alternate sudo lecture that will be used in place of the standard lecture if the named file exists. By default, sudo uses a built-in lecture.

listpw

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

all: All the user's sudoers file entries for the current host must have the NOPASSWD flag set to avoid entering a password.
always: The user must always enter a password to use the -l option.
any: At least one of the user's sudoers file entries for the current host must have the NOPASSWD flag set to avoid entering a password.
never: The user need never enter a password to use the -l option.

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

logfile

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

mailerflags

Flags to use when invoking mailer. Defaults to -t

mailerpath

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

mailfrom

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

mailto

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

secure_path

Path used for every command run from sudo If you don't trust the people running sudo to have a sane PATH environment variable you may want to use this. Another use is if you want to have the ``root path'' be separate from the ``user path'' Users in the group specified by the exempt_group option are not affected by secure_path This option is not set by default.

syslog

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

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

verifypw

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

all: All the user's sudoers file entries for the current host must have the NOPASSWD flag set to avoid entering a password.
always: The user must always enter a password to use the -v option.
any: At least one of the user's sudoers file entries for the current host must have the NOPASSWD flag set to avoid entering a password.
never: The user need never enter a password to use the -v option.

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

Lists that can be used in a boolean context

env_check

Environment variables to be removed from the user's environment unless they are considered ``safe'' For all variables except TZ ``safe'' means that the variable's value does not contain any `%' or `/' characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. The TZ variable is considered unsafe if any of the following are true:

It consists of a fully-qualified path name, optionally prefixed with a colon (`:' ) that does not match the location of the zoneinfo directory.
It contains a .. path element.
It contains white space or non-printable characters.
It is longer than the value of PATH_MAX

The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the = += -= and ! operators respectively. Regardless of whether the env_reset option is enabled or disabled, variables specified by env_check will be preserved in the environment if they pass the aforementioned check. The global list of environment variables to check is displayed when sudo is run by root with the -V option.

env_delete

Environment variables to be removed from the user's environment when the env_reset option is not in effect. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the = += -= and ! operators respectively. The global list of environment variables to remove is displayed when sudo is run by root with the -V option. Note that many operating systems will remove potentially dangerous variables from the environment of any setuid process (such as sudo )

env_keep

Environment variables to be preserved in the user's environment when the env_reset option is in effect. This allows fine-grained control over the environment sudo -spawned processes will receive. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the = += -= and ! operators respectively. The global list of variables to keep is displayed when sudo is run by root with the -V option.

GROUP PROVIDER PLUGINS

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

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

The following group provider plugins are installed by default:

group_file

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

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

system_group

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

Defaults group_plugin=system_group.so

The group provider plugin API is described in detail in sudo_plugin8.

LOG FORMAT

~/.ssh/config can log events using either syslog(3) or a simple log file. The log format is almost identical in both cases.

Accepted command log entries

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

date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
    USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
    ENV=env_vars COMMAND=command

Where the fields are as follows:

date: The date the command was run. Typically, this is in the format ``MMM, DD, HH:MM:SS'' If logging via syslog(3), the actual date format is controlled by the syslog daemon. If logging to a file and the log_year option is enabled, the date will also include the year.
hostname: The name of the host sudo was run on. This field is only present when logging via syslog(3).
progname: The name of the program, usually sudo or sudoedit This field is only present when logging via syslog(3).
username: The login name of the user who ran sudo
ttyname: The short name of the terminal (e.g. ``console'' ``tty01'' or ``pts/0'' sudo was run on, or ``unknown'' if there was no terminal present.
cwd: The current working directory that sudo was run in.
runasuser: The user the command was run as.
runasgroup: The group the command was run as if one was specified on the command line.
logid: An I/O log identifier that can be used to replay the command's output. This is only present when the log_input or log_output option is enabled.
env_vars: A list of environment variables specified on the command line, if specified.
command: The actual command that was executed.

Messages are logged using the locale specified by sudoers_locale which defaults to the ``C '' locale.

Denied command log entries

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

user NOT in sudoers: The user is not listed in the sudoers file.
user NOT authorized on host: The user is listed in the sudoers file but is not allowed to run commands on the host.
command not allowed: The user is listed in the sudoers file for the host but they are not allowed to run the specified command.
3 incorrect password attempts: The user failed to enter their password after 3 tries. The actual number of tries will vary based on the number of failed attempts and the value of the passwd_tries option.
a password is required: sudo 's -n option was specified but a password was required.
sorry, you are not allowed to set the following environment variables: The user specified environment variables on the command line that were not allowed by sudoers

Error log entries

If an error occurs, ~/.ssh/config 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: ~/.ssh/config 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): 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, ~/.ssh/config 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 ~/.ssh/config Plugin line in the sudo.conf5 file.
unable to stat /etc/sudoers: The /etc/sudoers file is missing.
/etc/sudoers is not a regular file: The /etc/sudoers file exists but is not a regular file or symbolic link.
/etc/sudoers is owned by uid N, should be 0: The sudoers file has the wrong owner. If you wish to change the sudoers file owner, please add ``sudoers_uid=N'' (where `N' is the user ID that owns the sudoers file) to the ~/.ssh/config Plugin line in the sudo.conf5 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 ~/.ssh/config Plugin line in the sudo.conf5 file.
/etc/sudoers is owned by gid N, should be 1: The sudoers file has the wrong group ownership. If you wish to change the sudoers file group ownership, please add ``sudoers_gid=N'' (where `N' is the group ID that owns the sudoers file) to the ~/.ssh/config Plugin line in the sudo.conf5 file.
unable to open /var/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 /var/run/sudo is not searchable by group or other. The default mode for /var/run/sudo is 0711.
unable to write to /var/run/sudo/ts/username: sudoers was unable to write to the user's time stamp file.
/var/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.
/var/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 syslog daemon, not sudoers itself. As such, they may vary in format on different systems.

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

Notes on logging to a file

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

The progname and hostname fields are not present.
If the log_year option is enabled, the date will also include the year.
Lines that are longer than loglinelen characters (80 by default) are word-wrapped and continued on the next line with a four character indent. This makes entries easier to read for a human being, but makes it more difficult to use grep(1) on the log files. If the loglinelen option is set to 0 (or negated with a `!' ) , word wrap will be disabled.

I/O LOG FILES

When I/O logging is enabled, sudo will run the command in a pseudo-tty and log all user input and/or output. I/O is logged to the directory specified by the iolog_dir option Po /var/log/sudo-io by default Pc using a unique session ID that is included in the sudo log line, prefixed with ``TSID= '' The iolog_file option may be used to control the format of the session ID.

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

log: a text file containing the time the command was run, the name of the user who ran sudo the name of the target user, the name of the target group (optional), the terminal that sudo was run from, the number of rows and columns of the terminal, the working directory the command was run from and the path name of the command itself (with arguments if present)
timing: a log of the amount of time between, and the number of bytes in, each I/O log entry (used for session playback)
ttyin: input from the user's tty (what the user types)
stdin: input from a pipe or file
ttyout: output from the pseudo-tty (what the command writes to the screen)
stdout: standard output to a pipe or redirected to a file
stderr: standard error to a pipe or redirected to a file

All files other than log are compressed in gzip format unless the compress_io option has been disabled. Due to buffering, the I/O log data will not be complete until the sudo command has completed. The output portion of an I/O log file can be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.

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

Since each session's I/O logs are stored in a separate directory, traditional log rotation utilities cannot be used to limit the number of I/O logs. The simplest way to limit the number of I/O is by setting the maxseq option to the maximum number of logs you wish to store. Once the I/O log sequence number reaches maxseq it will be reset to zero and ~/.ssh/config 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
/var/run/sudo/ts: Directory containing time stamps for the sudoers security policy
/var/lib/sudo/lectured: Directory containing lecture status files for the sudoers security policy
/etc/environment: Initial environment for -i mode on AIX and Linux systems

EXAMPLES

Below are example sudoers file entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases

# Run X applications through sudo; HOME is used to find the
# .Xauthority file.  Note that other programs use HOME to find
# configuration files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"

# User alias specification
User_Alias      FULLTIMERS = millert, mikef, dowdy
User_Alias      PARTTIMERS = bostley, jwfox, crawl
User_Alias      WEBMASTERS = will, wendy, wim

# Runas alias specification
Runas_Alias     OP = root, operator
Runas_Alias     DB = oracle, sybase
Runas_Alias     ADMINGRP = adm, oper

# Host alias specification
Host_Alias      SPARC = bigtime, eclipse, moet, anchor :\
                SGI = grolsch, dandelion, black :\
                ALPHA = widget, thalamus, foobar :\
                HPPA = boa, nag, python
Host_Alias      CUNETS = 128.138.0.0/255.255.0.0
Host_Alias      CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias      SERVERS = master, mail, www, ns
Host_Alias      CDROM = orion, perseus, hercules

# Cmnd alias specification
Cmnd_Alias      DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
                        /usr/sbin/restore, /usr/sbin/rrestore,\
                        sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
                        /home/operator/bin/start_backups
Cmnd_Alias      KILL = /usr/bin/kill
Cmnd_Alias      PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias      SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias      HALT = /usr/sbin/halt
Cmnd_Alias      REBOOT = /usr/sbin/reboot
Cmnd_Alias      SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
                         /usr/local/bin/tcsh, /usr/bin/rsh,\
                         /usr/local/bin/zsh
Cmnd_Alias      SU = /usr/bin/su
Cmnd_Alias      PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less

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

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

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

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

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

FULLTIMERS      ALL = NOPASSWD: ALL

Full time sysadmins Po millert mikef and dowdy Pc may run any command on any host without authenticating themselves.

PARTTIMERS      ALL = ALL

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

jack            CSNETS = ALL

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

lisa            CUNETS = ALL

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

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

The operator user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory /usr/oper/bin/ Note that one command in the DUMPS Cmnd_Alias includes a sha224 digest, /home/operator/bin/start_backups This is because the directory containing the script is writable by the operator user. If the script is modified (resulting in a digest mismatch) it will no longer be possible to run it via sudo

joe             ALL = /usr/bin/su operator

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

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

%opers          ALL = (: ADMINGRP) /usr/sbin/

Users in the opers group may run commands in /usr/sbin/ as themselves with any group in the ADMINGRP Runas_Alias (the adm and oper groups).

The user pete is allowed to change anyone's password except for root on the HPPA machines. Because command line arguments are matched as a single, concatenated string, the `*' wildcard will match multiple words. This example assumes that passwd(1) does not take multiple user names on the command line. Note that on GNU systems, options to passwd(1) may be specified after the user argument. As a result, this rule will also allow:

passwd username --expire

which may not be desirable.

bob             SPARC = (OP) ALL : SGI = (OP) ALL

The user bob may run anything on the SPARC and SGI machines as any user listed in the OP Runas_Alias Po root and operator Pc


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 Po oracle or sybase Pc without giving a password.

john            ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*

On the ALPHA machines, user john may su to anyone except root but he is not allowed to specify any options to the su(1) command.

jen             ALL, !SERVERS = ALL

The user jen may run any command on any machine except for those in the SERVERS Host_Alias (master, mail, www and ns).

jill            SERVERS = /usr/bin/, !SU, !SHELLS

For any machine in the SERVERS Host_Alias jill may run any commands in the directory /usr/bin/ except for those commands belonging to the SU and SHELLS Cmnd_Aliases While not specifically mentioned in the rule, the commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the noexec option set.

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

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

matt            valkyrie = KILL

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

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

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

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

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

SECURITY NOTES

Limitations of the So ! Sc operator

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

bill    ALL = ALL, !SU, !SHELLS

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

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

Security implications of fast_glob

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

For example, given the following sudoers file entry:

john    ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
              /usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root

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

Preventing shell escapes

Once sudo executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass sudo 's access control and logging. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs.

There are two basic approaches to this problem:

restrict

Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though sudoedit is a better solution to running editors via sudo Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not is often unworkable.

noexec

Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually LD_PRELOAD to an alternate shared library. On such systems, sudo 's noexec functionality can be used to prevent a program run by sudo from executing any other programs. Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreign executables running under binary emulation are not affected.

The noexec feature is known to work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, HP-UX 11.x and AIX 5.3 and above. It should be supported on most operating systems that support the LD_PRELOAD environment variable. Check your operating system's manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if LD_PRELOAD is supported.

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

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

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

Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer approach is to give the user permission to run sudoedit (see below).

Secure editing

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

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

For example, to allow user operator to edit the ``message of the day'' file:

operator        sudoedit /etc/motd

The operator user then runs sudoedit as follows:

$ sudoedit /etc/motd

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

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

Time stamp file checks

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

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

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

sudoers will not honor time stamps set far in the future. Time stamps with a date greater than current_time + 2 * TIMEOUT will be ignored and sudoers will log and complain.

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

DEBUGGING

Versions 1.8.4 and higher of the ~/.ssh/config 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.conf5 file.

The ~/.ssh/config plugin uses the same debug flag format as the sudo front-end: subsystem @ priority

The priorities used by , 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 ~/.ssh/config plugin:

alias: User_Alias Runas_Alias Host_Alias and Cmnd_Alias processing
all: matches every subsystem
audit: BSM and Linux audit code
auth: user authentication
defaults: sudoers file Defaults settings
env: environment handling
ldap: LDAP-based sudoers
logging: logging support
match: matching of users, groups, hosts and netgroups in the sudoers file
netif: network interface handling
nss: network service switch handling in sudoers
parser: sudoers file parsing
perms: permission setting
plugin: The equivalent of main for the plugin.
pty: pseudo-tty related code
rbtree: redblack tree internals
sssd: SSSD-based sudoers
util: utility functions

For example:

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

For more information, see the sudo.conf5 manual.

AUTHORS

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

An Todd C. Miller

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

CAVEATS

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

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

BUGS

If you feel you have found a bug in sudo please submit a bug report at bugzilla.sudo.ws

SUPPORT

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

DISCLAIMER

sudo is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with sudo or www.sudo.ws/license.html for complete details.

sudoers • man page

sudoers • man page

sudoers (5)

Leading comments

NAME

DESCRIPTION

Configuring sudo.conf for sudoers

User Authentication

Logging

Command environment

SUDOERS FILE FORMAT

Quick guide to EBNF

Aliases

Defaults

User specification

Runas_Spec

SELinux_Spec

Tag_Spec

Wildcards

Exceptions to wildcard rules

Including other files from within sudoers

Other special characters and reserved words

SUDOERS OPTIONS

GROUP PROVIDER PLUGINS

LOG FORMAT

Accepted command log entries

Denied command log entries

Error log entries

Notes on logging via syslog

Notes on logging to a file

I/O LOG FILES

FILES

EXAMPLES

SECURITY NOTES

Limitations of the So ! Sc operator

Security implications of fast_glob

Preventing shell escapes

Secure editing

Time stamp file checks

DEBUGGING

SEE ALSO

AUTHORS

CAVEATS

BUGS

SUPPORT

DISCLAIMER

Installed via

Man Section

Document Date

References

Referenced By