sudoers(5)

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sudoers(5) - Linux man page

Name

sudoers - default sudo security policy module

Description

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

Authentication and logging

The sudoers security policy requires that most users authenticate themselves before they can usesudo. A password is not required if theinvoking 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. Unlikesu(1),whensudoers requires authentication, it validates the invoking user's credentials, not the target user's (or root's) credentials. This can be changedvia therootpw, 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 isconfigurable via themailto Defaults entry (described later) and defaults to root.

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

If sudo is run by root and the SUDO_USER environment variable is set, thesudoers policy will use this value to determine who the actual useris. 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 evenwhen invoked via a sudo-run script or program. Note, however, that thesudoers lookup is still done for root, not the user specified by SUDO_USER.

sudoers uses time stamp files for credential caching. Once a user has been authenticated, the time stamp is updated and the user may then use sudowithout a password for a short period of time (

                                                           5 minutes unlessoverridden by the timeout option).  By default, sudoers uses a tty-basedtime stamp which means that there is a separate time stamp for each of auser's login sessions.  The tty_tickets option can be disabled to forcethe use of a single time stamp for all of a user's sessions.sudoers can log both successful and unsuccessful attempts (as well aserrors) to syslog(3), a log file, or both.  By default, sudoers will logvia syslog(3) but this is changeable via the syslog and logfile Defaultssettings.sudoers also supports logging a command's input and output streams.  I/Ologging is not on by default but can be enabled using the log_input andlog_output Defaults flags as well as the LOG_INPUT and LOG_OUTPUT commandtags.Command environment     Since environment variables can influence program behavior, sudoersprovides a means to restrict which variables from the user's environmentare inherited by the command to be run.  There are two distinct wayssudoers can deal with environment variables.By default, the env_reset option is enabled.  This causes commands to beexecuted with a new, minimal environment.  On AIX (and Linux systemswithout 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 inaddition to variables from the invoking process permitted by theenv_check and env_keep options.  This is effectively a whitelist forenvironment variables.If, however, the env_reset option is disabled, any variables notexplicitly denied by the env_check and env_delete options are inheritedfrom the invoking process.  In this case, env_check and env_delete behavelike a blacklist.  Since it is not possible to blacklist all potentiallydangerous environment variables, use of the default env_reset behavior isencouraged.In all cases, environment variables with a value beginning with () areremoved as they could be interpreted as bash functions.  The list ofenvironment variables that sudo allows or denies is contained in theoutput of ''sudo -V'' when run as root.Note that the dynamic linker on most operating systems will removevariables that can control dynamic linking from the environment of setuidexecutables, including sudo.  Depending on the operating system this mayinclude _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others.These type of variables are removed from the environment before sudo evenbegins execution and, as such, it is not possible for sudo to preservethem.As a special case, if sudo's -i option (initial login) is specified,sudoers will initialize the environment regardless of the value ofenv_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 arealso included.  All other environment variables are removed.Finally, if the env_file option is defined, any variables present in thatfile will be set to their specified values as long as they would notconflict 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 themost specific match).

The sudoers grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly 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 ofproduction 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 readerswill 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) isoptional.  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 opposedto 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 underscorecharacters ('_'). A NAMEmust start with an uppercase letter. It is possible to put several alias definitions of the same type on a single line, joinedby a colon (':'). E.g.,

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

The definitions of what constitutes a valid alias member follow.

User_List ::= User |        User ',' User_ListUser ::= '!'* 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_Aliases. Each list item may be prefixed withzero or more '!' operators. An odd number of '!' operators negate the value of the item; an even number just cancel each other out.

A user name, uid, group, gid, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special 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 includedinside the quotes.

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

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

• Group in any domain: "%:Group [e-mail]"

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

Note that quotes around group names are optional. Unquoted strings must use a backslash ('\') to escape spaces and special characters. SeeOther specialcharacters 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_Aliases it can contain Runas_Aliases. Note that user names and groups are matched asstrings. 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_ListHost ::= '!'* 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 anitem may be negated with the '!' operator. If you do not specify a netmask along with the network number,sudo will query each of the local host'snetwork interfaces and, if the network number corresponds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may bespecified 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 namemay include shell-style wildcards (see theWildcards section below), but unless the host name command on your machine returns the fully qualified hostname, you'll need to use thefqdn option for wildcards to be useful. Note that sudo only inspects actual network interfaces; this means that IPaddress 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 thecase for non-networked systems.

Cmnd_List ::= Cmnd |        Cmnd ',' Cmnd_Listcommand name ::= file name |           file name args |           file name '""'Cmnd ::= '!'* command name |   '!'* directory |   '!'* "sudoedit" |   '!'* Cmnd_Alias

A Cmnd_List is a list of one or more command names, directories, and other aliases. A command name is a fully qualified file name which may includeshell-style wildcards (see theWildcards 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 runwithout 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 willbe 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 thewildcards if there are any). Note that the following characters must be escaped with a '\' if they are used in command arguments: ',', ':', '=', '\'. Thespecial command ''sudoedit'' is used to permit a user to runsudo with the -e option (or as sudoedit). It may take command line argumentsjust as a normal command does.

Defaults

Certain configuration options may be changed from their default values at run-time via one or more Default_Entry lines. These may affect all users on anyhost, 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 notinclude 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_ListDefault_Entry ::= Default_Type Parameter_ListParameter_List ::= Parameter |             Parameter ',' Parameter_ListParameter ::= 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 ("") whenthey 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 usethe -= operator to remove an element that does not exist in a list.

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

See SUDOERS OPTIONS for a list of supported Defaults parameters.

User specification

User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \        (':' Host_List '=' Cmnd_Spec_List)*Cmnd_Spec_List ::= Cmnd_Spec |             Cmnd_Spec ',' Cmnd_Spec_ListCmnd_Spec ::= Runas_Spec? SELinux_Spec? Tag_Spec* CmndRunas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |        'SETENV:' | 'NOSETENV:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' |        'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')

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

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

Runas_Spec

A Runas_Spec determines the user and/or the group that a command may be run as. A fully-specified Runas_Spec consists of two Runas_Lists (as defined above)separated by a colon (':') and enclosed in a set of parentheses. The first Runas_List indicates which users the command may be run as via sudo's-u option. The second defines a list of groups that can be specified viasudo's -g option. If both Runas_Lists are specified, the commandmay be run with any combination of users and groups listed in their respective Runas_Lists. If only the first is specified, the command may be run as any userin 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 userwith the group set to any listed in the Runas_List. If both Runas_Lists are empty, the command may only be run as the invoking user. If no Runas_Spec isspecified the command may be run asroot 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 tooperator:

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 isspecified 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 bythe 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 usertcm. E.g.

$ sudo -g dialer /usr/bin/cu

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

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

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

SELinux_Spec

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

Tag_Spec

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

NOPASSWD and PASSWD

By default, sudo requires that a user authenticate him or herself before running a command. This behavior can be modified via the NOPASSWD tag. Likea 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 withoutauthenticating himself. If we only wantray 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 theexempt_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 apassword. 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 currenthost. This behavior may be overridden via theverifypw and listpw options.

NOEXEC and EXEC

If sudo has been compiled with noexec support and the underlying operating system supports it, the NOEXEC tag can be used to prevent adynamically-linked executable from running further commands itself.

In the following example, user aaron may run /usr/bin/more and/usr/bin/vi but shell escapes will be disabled.

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

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

SETENV and NOSETENV

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

LOG_INPUT and NOLOG_INPUT

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

Wildcards

sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names and command line arguments in thesudoers file. Wildcard matching is done via thePOSIX glob(3) andfnmatch(3) routines. Note that these arenot regularexpressions.

*'          Matches any set of zero or more characters.

?' Matches any single character.

[...]' Matches any character in the specified range.

[!...]' Matches any character not in the specified range.

\x' For any character 'x', evaluates to 'x'. This is used to escape special characters such as: '*', '?', '[', and ']'.

POSIX character classes may also be used if your system's glob(3) andfnmatch(3) functions support them. However, because the ':' character has specialmeaning insudoers, it must be escaped. For example:

/bin/ls [[alpha]]*

Would match any file name beginning with a letter.

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

/usr/bin/*

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

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

Wildcards in command line arguments should be used with care. Because command line arguments are matched as a single, concatenated string, a wildcard suchas '?' or '*' can match multiple words. For example, while a sudoers entry like:

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

will allow command like:

$ sudo cat /var/log/messages.1

It will also allow:

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

which is probably not what was intended.

Exceptions to wildcard rules

The following exceptions apply to the above rules:

""'          If the empty string "" is the only command line argument inthe sudoers entry it means that command is not allowed to berun 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-widesudoers 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. Uponreaching the end of /etc/sudoers.local, the rest of/etc/sudoers will be processed. Files that are included may themselves include other files. Ahard 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 wasincluded from. For example, if/etc/sudoers contains the line:

#include sudoers.local

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

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

#include /etc/sudoers.%h

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

The #includedir directive can be used to create a sudo.d directory that the system package manager can dropsudoers rules into as part ofpackage 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 withpackage 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 runvisudo with the -f flag to edit the files directly.

Other special characters and reserved words

The pound sign ('#') is used to indicate a comment (unless it is part of a #include directive or unless it occurs in the context of a user name and isfollowed 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, areignored.

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 ownalias called ALL as the built-in alias will be used in preferenceto your own. Please note that usingALL can be dangerous since in a command context, it allows the user to runany command on the system.

An exclamation point ('!') can be used as a logical not operator both in analias and in front of a Cmnd. This allows one to exclude certainvalues. Note, however, that using a '!' in conjunction with the built-inALL alias to allow a user to run ''all but a few'' commands rarely works asintended (seeSECURITY 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 aUser Specification (

                                           '=', ':', '(', ')') is optional.The following characters must be escaped with a backslash ('\') when usedas 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, arelisted below.

Boolean Flags:

always_set_home

If enabled, sudo will set the HOME environment variable to the home directory of the target user (which is root unless the-u option is used).This effectively means that the -H option is always implied. Note that HOME is already set when the theenv_reset option is enabled, soalways_set_home is only effective for configurations where eitherenv_reset is disabled or HOME is present in the env_keep list. This flagisoff 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 beoverridden via the PASSWD and NOPASSWD tags. This flag ison by default.

closefrom_override
If set, the user may use sudo's -C option which overrides the default starting point at whichsudo 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 usingzlib. This flag ison by default when sudo is compiled withzlib support.

env_editor' If set, visudo will use the value of the EDITOR or VISUAL environment variables before falling back on the default editor list. Note thatthis 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-separatedlist 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 isonby default.

env_reset' If set, sudo will run the command in a minimal environment containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER, USERNAME andSUDO_* 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 inthe file specified by theenv_file option (if any). The default contents of the env_keep and env_check lists are displayed whensudo is run byroot with the -V option. If the secure_path option is set, its value will be used for the PATH environment variable. This flag ison bydefault.

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 (automounted). Thefast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do its matching. Thedisadvantage of fast_glob is that it is unable to match relative path names such as ./ls or ../bin/ls. This has security implications whenpath names that include globbing characters are used with the negation operator, '!', as such rules can be trivially bypassed. As such, this option should notbe used whensudoers contains rules that contain negated path names which include globbing characters. This flag isoff 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 evenmix the two). This option is only effective when the ''canonical'' host name, as returned by thegetaddrinfo() or gethostbyname() function, is afully-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 thatsources are queried for hosts name resolution is usually specified in the/etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or, insome 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 bysudoers. For example, the following hosts file line for the machine ''xyzzy'' has the fully-qualifieddomain 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 requiressudoers to make DNS lookups which renders sudo unusableif DNS stops working (for example if the machine is disconnected from the network). Also note that just like with the hosts file, you must use the''canonical'' name as DNS knows it. That is, you may not use a host alias (
CNAME entry) due to performance issues and the fact that there is no way to get all aliases from DNS.

This flag is off by default.

ignore_dot' If set, sudo will ignore "." or "" (both denoting current directory) in the PATH environment variable; the PATH itself is not modified.This flag ison 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 thatonly 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 tellssudo how to behave when no specific LDAP entries have been matched, thissudoOption is only meaningful for the cn=defaults section. This flag isoff by default.

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

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

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

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

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

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

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

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

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

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

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

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

mail_no_host' If set, mail will be sent to the mailto user if the invoking user exists in thesudoers file, but is not allowed to run commandson the current host. This flag isoff by default.

mail_no_perms' If set, mail will be sent to the mailto user if the invoking user is allowed to usesudo but the command they are trying is notlisted in their sudoers file entry or is explicitly denied. This flag isoff by default.

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

noexec' If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden by a EXEC tag. See the description ofNOEXEC and EXEC below as well as thePreventing shell escapes section at the end of this manual. This flag isoff 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 disablethis 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 theexecutable 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 isonby default.

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:''. Ifpassprompt_override is set, passprompt will always be used. This flag isoff by default.

preserve_groups
By default, sudo will initialize the group vector to the list of groups the target user is in. Whenpreserve_groups is set, the user's existinggroup vector is left unaltered. The real and effective group IDs, however, are still set to match the target user. This flag isoff 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 thatsudo has hung at this point. When pwfeedback is set, sudo will providevisual 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 passwordbeing entered. This flag isoff 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 loginsession and not via other means such ascron(8) or cgi-bin scripts. This flag isoff 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 doingsomething like ''sudo sudo /bin/sh''. Note, however, that turning offroot_sudo will also prevent root from running sudoedit. Disablingroot_sudo provides no real additional security; it exists purely for historical reasons. This flag ison by default.

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

runaspw' If set, sudo will prompt for the password of the user defined by therunas_default option (defaults to root) instead of the passwordof the invoking user. This flag isoff 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 theenv_reset option is enabled, soset_home is only effective for configurations where either env_reset is disabled or HOME is present in theenv_keep list. This flag isoff 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, itmay be desirable to change this behavior. This can be done by negating the set_logname option. Note that if theenv_reset option has not been disabled,entries in the env_keep list will override the value ofset_logname. This flag is on by default.

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

setenv' Allow the user to disable the env_reset option from the command line via the-E option. Additionally, environment variables set viathe command line are not subject to the restrictions imposed byenv_check, env_delete, or env_keep. As such, only trusted users should beallowed to set variables in this manner. This flag isoff 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 (theshell 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). Thisflag isoff 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 changesthat 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 onsystems that disable some potentially dangerous functionality when a program is run setuid. This option is only effective on systems that support either thesetreuid(2) or setresuid(2) system call. This flag isoff by default.

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

tty_tickets' If set, users must authenticate on a per-tty basis. With this flag enabled,sudo will use a file named for the tty the user is logged inon in the user's time stamp directory. If disabled, the time stamp of the directory is used instead. This flag ison by default.

umask_override' If set, sudo will set the umask as specified bysudoers without modification. This makes it possible to specify a morepermissive umask insudoers than the user's own umask and matches historical behavior. If umask_override is not set, sudo will set theumask to be the union of the user's umask and what is specified insudoers. This flag is off by default. If set, sudo will run the commandin a pseudo-pty even if no I/O logging is being gone. A malicious program run undersudo could conceivably fork a background process that retains to theuser's terminal device after the main program has finished executing. Use of this option will make that impossible. This flag isoff 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 theinvoking 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 thevisiblepw 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 isoff 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). Theclosefrom option can be used to specify a different file descriptor at which to start closing. The default is 3.

passwd_tries' The number of tries a user gets to enter his/her password beforesudo 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 thesyslog 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 ifminute granularity is insufficient, for example 2.5. The default is 5.

timestamp_timeout
Number of minutes that can elapse before sudo will ask for a passwd again. The timeout may include a fractional component if minute granularity isinsufficient, for example 2.5. The default is 5. Set this to 0 to always prompt for a password. If set to a value less than 0 the user's time stamp will neverexpire. 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 theunion of the user's umask and the value of theumask option, which defaults to 0022. This guarantees that sudo never lowers the umask whenrunning 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 EDITORenvironment variable if possible, or the first editor in the list that exists and is executable. The default is/usr/local/bin/vi.

iolog_dir' The top-level directory to use when constructing the path name for the input/output log directory. Only used if thelog_input orlog_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 thedirectory. 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 thelog_input or log_output options areenabled or when the LOG_INPUT or LOG_OUTPUT tags are present for a command. Note thatiolog_file may contain directory components. The default is''%{seq}''.

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

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

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

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

passprompt' The default prompt to use when asking for a password; can be overridden via the-p option or the SUDO_PROMPT environment variable. Thefollowing 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 thefqdn 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:''. The default SELinux role to use when constructing a new security context to run the command. The defaultrole may be overridden on a per-command basis insudoers or via command line options. This option is only available when sudo is built withSELinux 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, andwarning.

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 isinterpreted. Defaults to ''C''.

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

timestampowner' The owner of the time stamp directory and the time stamps stored therein. The default is root.

type' The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basisinsudoers 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 beingrun. Entries in this file should either be of the form ''VARIABLE=value'' or ''export VARIABLE=value''. The value may optionally be surrounded by single ordouble quotes. Variables in this file are subject to othersudo environment settings such as env_keep and env_check.

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

group_plugin
A string containing a sudoers group plugin with optional arguments. This can be used to implement support for the nonunix_group syntax describedearlier. The string should consist of the plugin path, either fully-qualified or relative to the/usr/libexec directory, followed by any configurationarguments the plugin requires. These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the string must beenclosed in double quotes ("").

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

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

For more information see sudo_plugin(5).

lecture'              This option controls when a short lecture will beprinted along with the password prompt.  It has thefollowing 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 ofnever being used. The default value isonce.

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,sudouses a built-in lecture.

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

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

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

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

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

If no value is specified, a value of any is implied. Negating the option results in a value ofnever being used. The default value isany.

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. Bydefault,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 protectagainstsudo interpreting the @ sign. Defaults to the name of the user runningsudo.

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

secure_path
Path used for every command run from sudo. If you don't trust the people runningsudo to have a sane PATH environment variable you may want touse this. Another use is if you want to have the ''root path'' be separate from the ''user path''. Users in the group specified by theexempt_groupoption 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 runssudo with the -v option. It has the following possiblevalues:

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

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

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

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

If no value is specified, a value of all is implied. Negating the option results in a value ofnever being used. The default value isall.

Lists that can be used in a boolean context:

env_check' Environment variables to be removed from the user's environment if the variable's value contains '%' or '/' characters. This can be used to guardagainst printf-style format vulnerabilities in poorly-written programs. The argument may be a double-quoted, space-separated list or a single value withoutdouble-quotes. The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively. Regardless of whether theenv_reset option is enabled or disabled, variables specified by env_check will be preserved in the environment if they pass the aforementioned check. Thedefault list of environment variables to check is displayed whensudo is run by root with the -V option.

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

env_keep' Environment variables to be preserved in the user's environment when theenv_reset option is in effect. This allows fine-grained controlover the environmentsudo-spawned processes will receive. The argument may be a double-quoted, space-separated list or a single value withoutdouble-quotes. The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively. The default list ofvariables to keep is displayed when sudo is run by root with the-V option.

Log Format

sudoers can log events using either syslog(3) or a simple log file. In each case the log format is almost identical.

Accepted command log entries

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

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

Where the fields are as follows:

date'              The date the command was run.  Typically, this is inthe format ''MMM, DD, HH:MM:SS''.  If logging viasyslog(3), the actual date format is controlled by thesyslog daemon.  If logging to a file and the log_yearoption 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 viasyslog(3).

progname' The name of the program, usually sudo or sudoedit. This field is only present when logging viasyslog(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 thelog_input or log_output option isenabled.

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 thepasswd_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 bysudoers.

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

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

problem with defaults entries
The sudoers file contains one or more unknown Defaults settings. This does not preventsudo from running, but the sudoers file should bechecked usingvisudo.

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

unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can happen when thesudoers file is located on a remote file system that maps user ID 0 toa different value. Normally,sudoers tries to open sudoers using group permissions to avoid this problem. Consider changing the ownership of/etc/sudoers by adding an option like ''sudoers_uid=N'' (where 'N' is the user ID that owns thesudoers file) to the sudoers plugin linein the /etc/sudo.conf file.

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

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

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

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

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

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

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

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

Notes on logging via syslog
By default, sudoers logs messages via syslog(3). Thedate, hostname, and progname fields are added by the syslog daemon, notsudoers itself. As such, they may vary in format on different systems.

On most systems, syslog(3) has a relatively small log buffer. To prevent the command line arguments from being truncated,sudoers will split up logmessages that are larger than 960 characters (not including the date, hostname, and the string ''sudo''). When a message is split, additional parts willinclude 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 aformat similar tosyslog(3), with a few important differences:

1. The progname and hostname fields are not present.

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

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

SUDO.CONF

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

## Default /etc/sudo.conf file## Format:#   Plugin plugin_name plugin_path plugin_options ...#   Path askpass /path/to/askpass#   Path noexec /path/to/sudo_noexec.so#   Debug sudo /var/log/sudo_debug all@warn#   Set disable_coredump true## The plugin_path is relative to /usr/libexec unless#   fully qualified.# The plugin_name corresponds to a global symbol in the plugin#   that contains the plugin interface structure.# The plugin_options are optional.#Plugin policy_plugin sudoers.soPlugin io_plugin sudoers.so

Plugin options

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

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

The following plugin options are supported:

sudoers_file=pathname

The sudoers_file option can be used to override the default path to thesudoers file.

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

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

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

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

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

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

The following subsystems are used by sudoers:

alias' User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing

all' matches every subsystem

audit' BSM and Linux audit code

auth' user authentication

defaults
sudoers Defaults settings

env' environment handling

ldap' LDAP-based sudoers

logging
logging support

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

netif' network interface handling

nss' network service switch handling in sudoers

parser' sudoers file parsing

perms' permission setting

plugin' The equivalent of main for the plugin.

pty' pseudo-tty related code

rbtree' redblack tree internals

util' utility functions

Files

/etc/sudo.conf'                          Sudo front end configuration

/etc/sudoers' List of who can run what

/etc/group' Local groups file

/etc/netgroup' List of network groups

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

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

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

Examples

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

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

User_Alias

FULLTIMERS = millert, mikef, dowdy

User_Alias

PARTTIMERS = bostley, jwfox, crawl

User_Alias

WEBMASTERS = will, wendy, wim

# Runas alias specification

Runas_Alias

OP = root, operator

Runas_Alias

DB = oracle, sybase

Runas_Alias

ADMINGRP = adm, oper

# Host alias specification

Host_Alias

SPARC = bigtime, eclipse, moet, anchor :\

SGI = grolsch, dandelion, black :\

ALPHA = widget, thalamus, foobar :\

HPPA = boa, nag, python

Host_Alias

CUNETS = 128.138.0.0/255.255.0.0

Host_Alias

CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0

Host_Alias

SERVERS = master, mail, www, ns

Host_Alias

CDROM = orion, perseus, hercules

# Cmnd alias specification

Cmnd_Alias

DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\

/usr/sbin/restore, /usr/sbin/rrestore

Cmnd_Alias

KILL = /usr/bin/kill

Cmnd_Alias

PRINTING = /usr/sbin/lpc, /usr/bin/lprm

Cmnd_Alias

SHUTDOWN = /usr/sbin/shutdown

Cmnd_Alias

HALT = /usr/sbin/halt

Cmnd_Alias

REBOOT = /usr/sbin/reboot

Cmnd_Alias

SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\

/usr/local/bin/tcsh, /usr/bin/rsh,\

/usr/local/bin/zsh

Cmnd_Alias

SU = /usr/bin/su

Cmnd_Alias

PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less

Here we override some of the compiled in default values. We want sudo to log viasyslog(3) using theauth facility in all cases. We don't wantto subject the full time staff to thesudo lecture, user millert need not give a password, and we don't want to reset the LOGNAME, USER orUSERNAME environment variables when running commands as root. Additionally, on the machines in theSERVERS Host_Alias, we keep an additional local logfile 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 thecommands in the PAGERS Cmnd_Alias (

                                                  /usr/bin/more, /usr/bin/pgand /usr/bin/less).    # Override built-in defaults

Defaults

syslog=auth
Defaults>root

!set_logname
Defaults:FULLTIMERS

!lecture
Defaults:millert

!authenticate
Defaults@SERVERS

log_year, logfile=/var/log/sudo.log
Defaults!PAGERS

noexec

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

root            ALL = (ALL) ALL

%wheel

ALL = (ALL) ALL

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

FULLTIMERS      ALL = NOPASSWD: ALL

Full time sysadmins (

                            millert, mikef, and dowdy) may run any command onany 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 theentry 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 thosenetworks, 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 localmachine'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 printingsystem, shutting down the system, and any commands in the directory/usr/oper/bin/.

joe             ALL = /usr/bin/su operator

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

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

%opers

ALL = (: ADMINGRP) /usr/sbin/

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

The user pete is allowed to change anyone's password except for root on theHPPA machines. Note that this assumes passwd(1) does not takemultiple user names on the command line.

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

The user bob may run anything on the SPARC and SGI machines as any user listed in theOP Runas_Alias (

                                     root and operator.)    jim             +biglab = ALL

The user jim may run any command on machines in the biglab netgroup.sudo knows that ''biglab'' is a netgroup due to the '+' prefix.

+secretaries    ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser

Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on allmachines.

fred            ALL = (DB) NOPASSWD: ALL

The user fred can run commands as any user in the DB Runas_Alias (

     oracle or sybase) without giving a password.    john            ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*

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

jen             ALL, !SERVERS = ALL

The user jen may run any command on any machine except for those in theSERVERS 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 tothe SU and SHELLS Cmnd_Aliases.

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

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

matt            valkyrie = KILL

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

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 simplysu(1) to www.

ALL             CDROM = NOPASSWD: /sbin/umount /CDROM,\

/sbin/mount -o nosuidnodev /dev/cd0a /CDROM

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

Security Notes

Limitations of the '

!' operator

It is generally not effective to ''subtract'' commands from ALL using the '!' operator. A user can trivially circumvent this by copying the desiredcommand 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 inSU or SHELLS since he can simply copy those commands to a differentname, or use a shell escape from an editor or other program. Therefore, these kind of restrictions should be considered advisory at best (and reinforced bypolicy).

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 owncopy 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'sfnmatch(3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grantprivileges, it can result in a security issue for rules that subtract or revoke privileges.

For example, given the following sudoers entry:

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

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

Preventing shell escapes

Once sudo executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it isnot uncommon for a program to allow shell escapes, which lets a user bypasssudo's access control and logging. Common programs that permit shell escapesinclude 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,thoughsudoedit is a better solution to running editors via sudo. Due to the large number of programs that offer shell escapes, restricting usersto 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 (usuallyLD_PRELOAD) to an alternate shared library. On such systems,sudo's noexec functionality can be used to prevent a program run bysudo fromexecuting any other programs. Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreignexecutables 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 besupported 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 fromexecuting other commands (such as a shell). If you are unsure whether or not your system is capable of supportingnoexec you can always just try it outand check whether shell escapes work whennoexec 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 changingor 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 torun sudoedit.

Time stamp file checks

sudoers will check the ownership of its time stamp directory (

     /var/db/sudo by default) and ignore the directory's contents if it is notowned by root or if it is writable by a user other than root.  On systemsthat allow non-root users to give away files via chown(2), if the timestamp directory is located in a world-writable directory (e.g., /tmp), itis possible for a user to create the time stamp directory before sudo isrun.  However, because sudoers checks the ownership and mode of thedirectory and its contents, the only damage that can be done is to''hide'' files by putting them in the time stamp dir.  This is unlikelyto happen since once the time stamp dir is owned by root and inaccessibleby any other user, the user placing files there would be unable to getthem back out.sudoers will not honor time stamps set far in the future.  Time stampswith a date greater than current_time + 2 * TIMEOUT will be ignored andsudo will log and complain.  This is done to keep a user from creatinghis/her own time stamp with a bogus date on systems that allow users togive away files if the time stamp directory is located in aworld-writable directory.On systems where the boot time is available, sudoers will ignore timestamps that date from before the machine booted.Since time stamp files live in the file system, they can outlive a user'slogin session.  As a result, a user may be able to login, run a commandwith sudo after authenticating, logout, login again, and run sudo withoutauthenticating so long as the time stamp file's modification time iswithin 5 minutes (or whatever the timeout is set to in sudoers).  Whenthe tty_tickets option is enabled, the time stamp has per-tty granularitybut still may outlive the user's session.  On Linux systems where thedevpts filesystem is used, Solaris systems with the devices filesystem,as well as other systems that utilize a devfs filesystem thatmonotonically increase the inode number of devices as they are created(such as Mac OS X), sudoers is able to determine when a tty-based timestamp file is stale and will ignore it.  Administrators should not relyon this feature as it is not universally available.

See Also

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

Caveats

The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperativethatsudoers be free of syntax errors since sudo will not run with a syntactically incorrectsudoers 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 tohave the machine's host name be fully qualified as returned by the hostname command or use thefqdn option in sudoers.

Bugs

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

Support

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

Disclaimer

sudo is provided ''AS IS'' and any express or implied warranties, including, but not limited to, the implied warranties of merchantability andfitness for a particular purpose are disclaimed. See the LICENSE file distributed withsudo or http://www.sudo.ws/sudo/license.html for completedetails.

Sudo 1.8.6p3 July 16, 2012 Sudo 1.8.6p3

Referenced By

slog(8),sslogger(8),sssd-sudo(5)