sudoers - list of which users may execute what
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 grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you don't know what EBNF is; it is fairly simple, and the definitions below are annotated.
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).
There are four kinds of aliases:
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
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
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
User_List is made up of one or more user names, user ids (prefixed with '#'), system group names and ids (prefixed with '%' and '%#' respectively), netgroups (prefixed with '+'), non-Unix group names and IDs (prefixed with '%:' and '%:#' respectively) and
User_Aliases. Each list item may be prefixed with zero or more '!' operators. An odd number of '!' operators negate the value of the item; an even number just cancel each other out.
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.
nonunix_gid syntax depends on the underlying implementation. For instance, the QAS AD backend supports the following formats:
Group in the same domain: "Group Name"
Group in any domain: "Group Name@FULLY.QUALIFIED.DOMAIN"
Group SID: "S-1-2-34-5678901234-5678901234-5678901234-567"
Note that quotes around group names are optional. Unquoted strings must use a backslash (\) to escape spaces and special characters. See "Other special characters and reserved words" for a list of characters that need to be escaped.
Runas_List ::= Runas_Member | Runas_Member ',' Runas_List Runas_Member ::= '!'* user name | '!'* #uid | '!'* %group | '!'* %#gid | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* +netgroup | '!'* Runas_Alias
Runas_List is similar to a
User_List except that instead of
User_Aliases it can contain
Runas_Aliases. Note that user names and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are considered to be distinct. If you wish to match all user names with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given).
Host_List ::= Host | Host ',' Host_List Host ::= '!'* host name | '!'* ip_addr | '!'* network(/netmask)? | '!'* +netgroup | '!'* Host_Alias
Host_List is made up of one or more host names, IP addresses, network numbers, netgroups (prefixed with '+') and other aliases. Again, the value of an item may be negated with the '!' operator. If you do not specify a netmask along with the network number, sudo will query each of the local host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may be specified either in standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g. 24 or 64). A host name may include shell-style wildcards (see the Wildcards section below), but unless the
host name command on your machine returns the fully qualified host name, you'll need to use the fqdn option for wildcards to be useful. Note sudo only inspects actual network interfaces; this means that IP address 127.0.0.1 (localhost) will never match. Also, the host name "localhost" will only match if that is the actual host name, which is usually only the case for non-networked systems.
Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List commandname ::= file name | file name args | file name '""' Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias
Cmnd_List is a list of one or more commandnames, directories, and other aliases. A commandname is a fully qualified file name which may include shell-style wildcards (see the Wildcards section below). A simple file name allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify
"" to indicate that the command may only be run without command line arguments. A directory is a fully qualified path name ending in a '/'. When you specify a directory in a
Cmnd_List, the user will be able to run any file within that directory (but not in any subdirectories therein).
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 special 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.
Certain configuration options may be changed from their default values at runtime 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,
-=. 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 "SUDOERS OPTIONS" for a list of supported Defaults parameters.
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 ::= ('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 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 determines the user and/or the group that a command may be run as. A fully-specified
Runas_Spec consists of two
Runas_Lists (as defined above) separated by a colon (':') and enclosed in a set of parentheses. The first
Runas_List indicates which users the command may be run as via sudo's -u option. The second defines a list of groups that can be specified via sudo's -g option. If both
Runas_Lists are specified, the command may be run with any combination of users and groups listed in their respective
Runas_Lists. If only the first is specified, the command may be run as any user in the list but no -g option may be specified. If the first
Runas_List is empty but the second is specified, the command may be run as the invoking user with the group set to any listed in the
Runas_List. If no
Runas_Spec is specified the command may be run as root and no group may be specified.
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.
On systems with SELinux support, sudoers entries may optionally have an SELinux role and/or type associated with a command. If a role or type is specified with the command it will override any default values specified in sudoers. A role or type specified on the command line, however, will supercede the values in sudoers.
A command may have zero or more tags associated with it. There are eight possible tag values,
NOLOG_OUTPUT. Once a tag is set on a
Cmnds in the
Cmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (i.e.:
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
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.
If sudo has been compiled with noexec support and the underlying operating system supports it, the
NOEXEC tag can be used to prevent a dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the PREVENTING SHELL ESCAPES section below for more details on how
NOEXEC works and whether or not it will work on your system.
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
These tags override the value of the log_input option on a per-command basis. For more information, see the description of log_input in the "SUDOERS OPTIONS" section below.
These tags override the value of the log_output option on a per-command basis. For more information, see the description of log_output in the "SUDOERS OPTIONS" section below.
sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names and command line arguments in the sudoers file. Wildcard matching is done via the POSIX glob(3) and fnmatch(3) routines. Note that these are not regular expressions.
Matches any set of zero or more characters.
Matches any single character.
Matches any character in the specified range.
Matches any character not in the specified range.
For any character "x", evaluates to "x". This is used to escape special characters such as: "*", "?", "[", and "}".
POSIX character classes may also be used if your system's glob(3) and fnmatch(3) functions support them. However, because the
':' character has special meaning in sudoers, it must be escaped. For example:
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. When matching the command line arguments, however, a slash does get matched by wildcards. This is to make a path like:
match /usr/bin/who but not /usr/bin/X11/xterm.
The following exceptions apply to the above rules:
If the empty string
"" is the only command line argument in the sudoers entry it means that command is not allowed to be run with any arguments.
It is possible to include other sudoers files from within the sudoers file currently being parsed using the
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 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:
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:
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. I.e., if the machine's host name is "xerxes", then
will cause sudo to include the file /etc/sudoers.xerxes.
#includedir directive can be used to create a sudo.d directory that the system package manager can drop sudoers rules into as part of package installation. For example, given:
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.
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
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 both in an alias and in front of a
Cmnd. This allows one to exclude certain values. Note, however, that using a
! in conjunction with the built-in
ALL alias to allow a user to run "all but a few" commands rarely works as intended (see SECURITY NOTES below).
Long lines can be continued with a backslash ('\') as the last character on the line.
Whitespace between elements in a list as well as special syntactic characters in a User Specification ('=', ':', '(', ')') is optional.
The following characters must be escaped with a backslash ('\') when used as part of a word (e.g. a user name or host name): '!', '=', ':', ',', '(', ')', '\'.
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.
If enabled, sudo will set the
HOME environment variable to the home directory of the target user (which is root unless the -u option is used). This effectively means that the -H option is always implied. Note that
HOME is already set when the the env_reset option is enabled, so always_set_home is only effective for configurations where either env_reset is disabled or
HOME is present in the env_keep list. This flag is off by default.
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
NOPASSWD tags. This flag is on by default.
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.
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.
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 off by default.
If set, sudo will run the command in a minimal environment containing the
SUDO_ variables. Any variables in the caller's environment that match the
env_check lists are then added, followed by any variables present in the file specified by the env_file option (if any). The default contents of the
env_check lists are displayed when sudo is run by root with the -V option. If the secure_path option is set, its value will be used for the
PATH environment variable. This flag is on by default.
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). 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 sudoers contains rules that contain negated path names which include globbing characters. This flag is off by default.
Set this flag if you want to put fully qualified host names in the sudoers file. I.e., instead of myhost you would use myhost.mydomain.edu. You may still use the short form if you wish (and even mix the two). Beware that turning on fqdn requires sudo to make DNS lookups which may make sudo unusable if DNS stops working (for example if the machine is not plugged into the network). Also note that you must use the host's official 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. If your machine's host name (as returned by the
hostname command) is already fully qualified you shouldn't need to set fqdn. This flag is off by default.
If set, sudo will ignore '.' or '' (current dir) in the
PATH environment variable; the
PATH itself is not modified. This flag is off by default.
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.
If set, sudo will insult users when they enter an incorrect password. This flag is off by default.
If set, the host name will be logged in the (non-syslog) sudo log file. This flag is off by default.
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 normal sudo log line, prefixed with TSID=.
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 is all that is required.
If set, sudo will run the command in a pseudo tty and log all output that is sent to the screen, similar to the script(1) command. If the standard output or 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 output is also captured and stored in separate log files.
Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.
Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.
If set, the four-digit year will be logged in the (non-syslog) sudo log file. This flag is off by default.
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.
Send mail to the mailto user every time a users runs sudo. This flag is off by default.
Send mail to the mailto user if the user running sudo does not enter the correct password. This flag is off by default.
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.
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.
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.
If set, all commands run via sudo will behave as if the
NOEXEC tag has been set, unless overridden by a
EXEC tag. See the description of NOEXEC and EXEC below as well as the "PREVENTING SHELL ESCAPES" section at the end of this manual. This flag is off by default.
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.
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.
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.
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.
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.
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.
If set, sudo will prompt for the root password instead of the password of the invoking user. This flag is off by default.
If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to
root) instead of the password of the invoking user. This flag is off by default.
If enabled and sudo is invoked with the -s option the
HOME environment variable will be set to the home directory of the target user (which is root unless the -u option is used). This effectively makes the -s option imply -H. Note that
HOME is already set when the the env_reset option is enabled, so set_home is only effective for configurations where either env_reset is disabled or
HOME is present in the env_keep list. This flag is off by default.
Normally, sudo will set the
USERNAME environment variables to the name of the target user (usually root unless the -u option is given). However, since some programs (including the RCS revision control system) use
LOGNAME to determine the real identity of the user, it may be desirable to change this behavior. This can be done by negating the set_logname option. Note that if the env_reset option has not been disabled, entries in the env_keep list will override the value of set_logname. This flag is on by default.
Allow the user to disable the env_reset option from the command line. 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.
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.
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 with either the setreuid() or setresuid() function. This flag is off by default.
If set, sudo will prompt for the password of the user specified by the -u option (defaults to
root) instead of the password of the invoking user. In addition, the timestamp file name will include the target user's name. Note that this flag precludes the use of a uid not listed in the passwd database as an argument to the -u option. This flag is off by default.
If set, users must authenticate on a per-tty basis. With this flag enabled, sudo will use a file named for the tty the user is logged in on in the user's time stamp directory. If disabled, the time stamp of the directory is used instead. This flag is on by default.
If set, sudo will set the umask as specified by sudoers without modification. This makes it possible to specify a more permissive umask in sudoers than the user's own umask and matches historical behavior. If umask_override is not set, sudo will set the umask to be the union of the user's umask and what is specified in sudoers. This flag is off by default.
If set, sudo will apply the defaults specified for the target user's login class if one exists. Only available if sudo is configured with the --with-logincap option. This flag is off by default.
If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone. A malicious program run under sudo could conceivably fork a background process that retains to the user's terminal device after the main program has finished executing. Use of this option will make that impossible.
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
"rsh somehost sudo ls" since rsh(1) does not allocate a tty. This flag is off by default.
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
The number of tries a user gets to enter his/her password before sudo logs the failure and exits. The default is
Integers that can be used in a boolean context:
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).
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
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
5. Set this to
0 to always prompt for a password. If set to a value less than
0 the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via
sudo -v and
sudo -k respectively.
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.
Message that is displayed if a user enters an incorrect password. The default is
Sorry, try again. unless insults are enabled.
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
The directory in which to store input/output logs when the log_input or log_output options are enabled or when the
LOG_OUTPUT tags are present for a command. The default is
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 ***.
Path to a shared library containing dummy versions of the execv(), execve() and fexecve() library functions that just return an error. This is used to implement the noexec functionality on systems that support
LD_PRELOAD or its equivalent. Defaults to /usr/local/libexec/sudo_noexec.so.
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 (`
%') escapes are supported:
expanded to the local host name including the domain name (on if the machine's host name is fully qualified or the fqdn option is set)
expanded to the local host name without the domain name
expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
expanded to the login name of the user the command will be run as (defaults to root)
expanded to the invoking user's login name
% characters are collapsed into a single
The default value is
The default SELinux role to use when constructing a new security context to run the command. The default role may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.
The default user to run commands as if the -u option is not specified on the command line. This defaults to
Syslog priority to use when user authenticates unsuccessfully. Defaults to
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
Syslog priority to use when user authenticates successfully. Defaults to
See syslog_badpri for the list of supported syslog priorities.
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
The directory in which sudo stores its timestamp files. The default is /var/adm/sudo.
The owner of the timestamp directory and the timestamps stored therein. The default is
The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.
Strings that can be used in a boolean context:
The askpass option specifies the fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when sudo is executed from a graphical (as opposed to text-based) application. The program specified by askpass should display the argument passed to it as the prompt and write the user's password to the standard output. The value of askpass may be overridden by the
SUDO_ASKPASS environment variable.
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
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.
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.
This option controls when a short lecture will be printed along with the password prompt. It has the following possible values:
Always lecture the user.
Never lecture the user.
Only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is once.
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.
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 the user's sudoers entries for the current host must have the
NOPASSWD flag set to avoid entering a password.
The user must always enter a password to use the -l option.
At least one of the user's sudoers entries for the current host must have the
NOPASSWD flag set to avoid entering a password.
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.
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.
Flags to use when invoking mailer. Defaults to -t.
Path to mail program used to send warning mail. Defaults to the path to sendmail found at configure time.
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.
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
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 facility if syslog is being used for logging (negate to disable syslog logging). Defaults to
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
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 the user's sudoers entries for the current host must have the
NOPASSWD flag set to avoid entering a password.
The user must always enter a password to use the -v option.
At least one of the user's sudoers entries for the current host must have the
NOPASSWD flag set to avoid entering a password.
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:
Environment variables to be removed from the user's environment if the variable's value contains
/ characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. 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
! operators respectively. Regardless of whether the
env_reset option is enabled or disabled, variables specified by
env_check will be preserved in the environment if they pass the aforementioned check. The default list of environment variables to check is displayed when sudo is run by root with the -V option.
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
! 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 as sudo).
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
! operators respectively. The default list of variables to keep is displayed when sudo is run by root with the -V option.
List of who can run what
Local groups file
List of network groups
I/O log files
Below are example sudoers entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the Defaults env_keep += "DISPLAY HOME" User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase Runas_Alias ADMINGRP = adm, oper Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 18.104.22.168/255.255.0.0 Host_Alias CSNETS = 22.214.171.124, 126.96.36.199/24, 188.8.131.52 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to log via syslog(3) using the auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user millert need not give a password, and we don't want to reset the
USERNAME environment variables when running commands as root. Additionally, on the machines in the SERVERS
Host_Alias, we keep an additional local log file and make sure we log the year in each log line since the log entries will be kept around for several years. Lastly, we disable shell escapes for the commands in the PAGERS
Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less).
# Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL %wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (bostley, jwfox, and crawl) may run any command on any host but they must authenticate themselves first (since the entry lacks the
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks
184.108.40.206). Of those networks, only
220.127.116.11 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
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory /usr/oper/bin.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root %opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin as themselves with any group in the ADMINGRP
Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on the HPPA machines. Note that this assumes passwd(1) does not take multiple user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user listed in the OP
Runas_Alias (root and operator).
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo knows that "biglab" is a netgroup due to the '+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB
Runas_Alias (oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the SERVERS
Host_Alias (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS
Host_Alias, jill may run any commands in the directory /usr/bin except for those commands belonging to the SU and SHELLS
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.
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).
Furthermore, 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 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.
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:
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.
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.
To tell whether or not sudo supports noexec, you can run the following as root:
sudo -V | grep "dummy exec"
If the resulting output contains a line that begins with:
File containing dummy exec functions:
then sudo may be able to replace the exec family of functions in the standard library with its own that simply return an error. Unfortunately, there is no foolproof way to know whether or not noexec will work at compile-time. noexec should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known not to work on AIX and UnixWare. noexec is expected to work 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 see if it works.
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.
The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperative that sudoers be free of syntax errors since sudo will not run with a 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.
If you feel you have found a bug in sudo, please submit a bug report at https://www.sudo.ws/sudo/bugs/
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
sudo is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with sudo or https://www.sudo.ws/sudo/license.html for complete details.