Provided by: sudo-ldap_1.8.16-0ubuntu1.10_amd64 
NAME
sudoers — default sudo security policy plugin
DESCRIPTION
The sudoers policy plugin determines a user's sudo privileges. It is the default sudo policy plugin.
The policy is driven by the /etc/sudoers file or, optionally in LDAP. The policy format is described in
detail in the “SUDOERS FILE FORMAT” section. For information on storing sudoers policy information in
LDAP, please see sudoers.ldap(5).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which policy and and I/O logging plugins to load. If no
sudo.conf(5) file is present, or if it contains no Plugin lines, sudoers will be used for policy
decisions and I/O logging. To explicitly configure sudo.conf(5) to use the sudoers plugin, the following
configuration can be used.
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional arguments to the sudoers plugin in the
sudo.conf(5) file. These arguments, if present, should be listed after the path to the plugin (i.e.
after sudoers.so). Multiple arguments may be specified, separated by white space. For example:
Plugin sudoers_policy sudoers.so sudoers_mode=0400
The following plugin arguments are supported:
ldap_conf=pathname
The ldap_conf argument can be used to override the default path to the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the default path to the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the default path to the sudoers file.
sudoers_uid=uid
The sudoers_uid argument can be used to override the default owner of the sudoers file. It
should be specified as a numeric user ID.
sudoers_gid=gid
The sudoers_gid argument can be used to override the default group of the sudoers file. It
must be specified as a numeric group ID (not a group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the default file mode for the sudoers file.
It should be specified as an octal value.
For more information on configuring sudo.conf(5), please refer to its manual.
User Authentication
The sudoers security policy requires that most users authenticate themselves before they can use sudo. A
password is not required if the invoking user is root, if the target user is the same as the invoking
user, or if the policy has disabled authentication for the user or command. Unlike su(1), when sudoers
requires authentication, it validates the invoking user's credentials, not the target user's (or root's)
credentials. This can be changed via the rootpw, targetpw and runaspw flags, described later.
If a user who is not listed in the policy tries to run a command via sudo, mail is sent to the proper
authorities. The address used for such mail is configurable via the mailto Defaults entry (described
later) and defaults to root.
Note that no mail will be sent if an unauthorized user tries to run sudo with the -l or -v option unless
there is an authentication error and either the mail_always or mail_badpass flags are enabled. This
allows users to determine for themselves whether or not they are allowed to use sudo. All attempts to
run sudo (successful or not) will be logged, regardless of whether or not mail is sent.
If sudo is run by root and the SUDO_USER environment variable is set, the sudoers policy will use this
value to determine who the actual user is. This can be used by a user to log commands through sudo even
when a root shell has been invoked. It also allows the -e option to remain useful even when invoked via
a sudo-run script or program. Note, however, that the sudoers file lookup is still done for root, not
the user specified by SUDO_USER.
sudoers uses per-user time stamp files for credential caching. Once a user has been authenticated, a
record is written containing the uid that was used to authenticate, the terminal session ID, and a time
stamp (using a monotonic clock if one is available). The user may then use sudo without a password for a
short period of time (15 minutes unless overridden by the timeout option). By default, sudoers uses a
separate record for each tty, which means that a user's login sessions are authenticated separately. The
tty_tickets option can be disabled to force the use of a single time stamp for all of a user's sessions.
Logging
sudoers can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file,
or both. By default, sudoers will log via syslog(3) but this is changeable via the syslog and logfile
Defaults settings. See “LOG FORMAT” for a description of the log file format.
sudoers is also capable of running a command in a pseudo-tty and logging all input and/or output. The
standard input, standard output and standard error can be logged even when not associated with a
terminal. I/O logging is not on by default but can be enabled using the log_input and log_output options
as well as the LOG_INPUT and LOG_OUTPUT command tags. See “I/O LOG FILES” for details on how I/O log
files are stored.
Command environment
Since environment variables can influence program behavior, sudoers provides a means to restrict which
variables from the user's environment are inherited by the command to be run. There are two distinct
ways sudoers can deal with environment variables.
By default, the env_reset option is enabled. This causes commands to be executed with a new, minimal
environment. On AIX (and Linux systems without PAM), the environment is initialized with the contents of
the /etc/environment file. The new environment contains the TERM, PATH, HOME, MAIL, SHELL, LOGNAME,
USER, USERNAME and SUDO_* variables in addition to variables from the invoking process permitted by the
env_check and env_keep options. This is effectively a whitelist for environment variables. Environment
variables with a value beginning with () are removed unless both the name and value parts are matched by
env_keep or env_check, as they will be interpreted as functions by older versions of the bash shell.
Prior to version 1.8.11, such variables were always removed.
If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and
env_delete options are inherited from the invoking process. In this case, env_check and env_delete
behave like a blacklist. Environment variables with a value beginning with () are always removed, even
if they do not match one of the blacklists. Since it is not possible to blacklist all potentially
dangerous environment variables, use of the default env_reset behavior is encouraged.
By default, environment variables are matched by name. However, if the pattern includes an equal sign
(‘=’), both the variables name and value must match. For example, an old-style (pre-shellshock) bash
shell function could be matched as follows:
env_keep += "my_func=()*"
Without the “=()*” suffix, this would not match, as old-style bash shell functions are not preserved by
default.
The complete list of environment variables that sudo allows or denies is contained in the output of “sudo
-V” when run as root. Please note that this list varies based on the operating system sudo is running
on.
On systems that support PAM where the pam_env module is enabled for sudo, variables in the PAM
environment may be merged in to the environment. If a variable in the PAM environment is already present
in the user's environment, the value will only be overridden if the variable was not preserved by
sudoers. When env_reset is enabled, variables preserved from the invoking user's environment by the
env_keep list take precedence over those in the PAM environment. When env_reset is disabled, variables
present the invoking user's environment take precedence over those in the PAM environment unless they
match a pattern in the env_delete list.
Note that the dynamic linker on most operating systems will remove variables that can control dynamic
linking from the environment of setuid executables, including sudo. Depending on the operating system
this may include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others. These type of variables
are removed from the environment before sudo even begins execution and, as such, it is not possible for
sudo to preserve them.
As a special case, if sudo's -i option (initial login) is specified, sudoers will initialize the
environment regardless of the value of env_reset. The DISPLAY, PATH and TERM variables remain unchanged;
HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user. On AIX (and Linux systems without
PAM), the contents of /etc/environment are also included. All other environment variables are removed.
Finally, if the env_file option is defined, any variables present in that file will be set to their
specified values as long as they would not conflict with an existing environment variable.
SUDOERS FILE FORMAT
The sudoers file is composed of two types of entries: aliases (basically variables) and user
specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are multiple matches, the
last match is used (which is not necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if
you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up
of production rules. E.g.,
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains
the following operators, which many readers will recognize from regular expressions. Do not, however,
confuse them with “wildcard” characters, which have different meanings.
? Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or
not at all.
* Means that the preceding symbol (or group of symbols) may appear zero or more times.
+ Means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to
designate what is a verbatim character string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* |
'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
'Host_Alias' Host_Alias (':' Host_Alias)* |
'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
User_Alias ::= NAME '=' User_List
Runas_Alias ::= NAME '=' Runas_List
Host_Alias ::= NAME '=' Host_List
Cmnd_Alias ::= NAME '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of
uppercase letters, numbers, and underscore characters (‘_’). A NAME must start with an uppercase letter.
It is possible to put several alias definitions of the same type on a single line, joined by a colon
(‘:’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to use the same name for aliases of
different types, but this is not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user IDs (prefixed with ‘#’), system group names and
IDs (prefixed with ‘%’ and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix group names and
IDs (prefixed with ‘%:’ and ‘%:#’ respectively) and User_Aliases. Each list item may be prefixed with
zero or more ‘!’ operators. An odd number of ‘!’ operators negate the value of the item; an even number
just cancel each other out. User netgroups are matched using the user and domain members only; the host
member is not used when matching.
A user name, uid, group, gid, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to
avoid the need for escaping special characters. Alternately, special characters may be specified in
escaped hex mode, e.g. \x20 for space. When using double quotes, any prefix characters must be included
inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin. For
instance, the QAS AD plugin supports the following formats:
• Group in the same domain: "%:Group Name"
• Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
• Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See “GROUP PROVIDER PLUGINS” for more information.
Note that quotes around group names are optional. Unquoted strings must use a backslash (‘\’) to escape
spaces and special characters. See “Other special characters and reserved words” for a list of
characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
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 as strings. In other words, two users (groups) with the same
uid (gid) are considered to be distinct. If you wish to match all user names with the same uid (e.g.
root and toor), you can use a uid instead (#0 in the example given).
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias
A Host_List is made up of one or more host names, IP addresses, network numbers, netgroups (prefixed with
‘+’) and other aliases. Again, the value of an item may be negated with the ‘!’ operator. Host
netgroups are matched using the host (both qualified and unqualified) and domain members only; the user
member is not used when matching. If you specify a network number without a netmask, sudo will query
each of the local host's network interfaces and, if the network number corresponds to one of the hosts's
network interfaces, will use the netmask of that interface. The netmask may be specified either in
standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of
bits, e.g. 24 or 64). A host name may include shell-style wildcards (see the “Wildcards” section below),
but unless the host name command on your machine returns the fully qualified host name, you'll need to
use the fqdn option for wildcards to be useful. Note that sudo only inspects actual network interfaces;
this means that IP address 127.0.0.1 (localhost) will never match. Also, the host name “localhost” will
only match if that is the actual host name, which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[[A-Za-z0-9+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Cmnd ::= Digest_Spec? '!'* command name |
'!'* directory |
'!'* "sudoedit" |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more command names, directories, and other aliases. A command name is a
fully qualified file name which may include shell-style wildcards (see the “Wildcards” section below). A
simple file name allows the user to run the command with any arguments he/she wishes. However, you may
also specify command line arguments (including wildcards). Alternately, you can specify "" to indicate
that the command may only be run without command line arguments. A directory is a fully qualified path
name ending in a ‘/’. When you specify a directory in a Cmnd_List, the user will be able to run any file
within that directory (but not in any sub-directories therein).
If a Cmnd has associated command line arguments, then the arguments in the Cmnd must match exactly those
given by the user on the command line (or match the wildcards if there are any). Note that the following
characters must be escaped with a ‘\’ if they are used in command arguments: ‘,’, ‘:’, ‘=’, ‘\’. The
built-in command “sudoedit” is used to permit a user to run sudo with the -e option (or as sudoedit). It
may take command line arguments just as a normal command does. Note that “sudoedit” is a command built
into sudo itself and must be specified in the sudoers file without a leading path.
If a command name is prefixed with a Digest_Spec, the command will only match successfully if it can be
verified using the specified SHA-2 digest. The following digest formats are supported: sha224, sha256,
sha384 and sha512. The string may be specified in either hex or base64 format (base64 is more compact).
There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum,
sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself (directly or via a sudo command), it may be
possible for the user to replace the command after the digest check has been performed but before the
command is executed. A similar race condition exists on systems that lack the fexecve(2) system call
when the directory in which the command is located is writable by the user.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default values at run-time via one or more
Default_Entry lines. These may affect all users on any host, all users on a specific host, a specific
user, a specific command, or commands being run as a specific user. Note that per-command entries may
not include command line arguments. If you need to specify arguments, define a Cmnd_Alias and reference
that instead.
Default_Type ::= 'Defaults' |
'Defaults' '@' Host_List |
'Defaults' ':' User_List |
'Defaults' '!' Cmnd_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are implicitly boolean and can be
turned off via the ‘!’ operator. Some integer, string and list parameters may also be used in a boolean
context to disable them. Values may be enclosed in double quotes ("") when they contain multiple words.
Special characters may be escaped with a backslash (‘\’).
Lists have two additional assignment operators, += and -=. These operators are used to add to and delete
from a list respectively. It is not an error to use the -= operator to remove an element that does not
exist in a list.
Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas
Defaults and finally command defaults.
See “SUDOERS OPTIONS” for a list of supported Defaults parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? SELinux_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Tag_Spec ::= ('EXEC:' | 'NOEXEC:' | 'FOLLOW:' | 'NOFOLLOW' |
'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' |
'NOLOG_OUTPUT:' | 'MAIL:' | 'NOMAIL:' | 'PASSWD:' |
'NOPASSWD:' | 'SETENV:' | 'NOSETENV:')
A user specification determines which commands a user may run (and as what user) on specified hosts. By
default, commands are run as root, but this can be changed on a per-command basis.
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into
its constituent parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be run as. A fully-specified
Runas_Spec consists of two Runas_Lists (as defined above) separated by a colon (‘:’) and enclosed in a
set of parentheses. The first Runas_List indicates which users the command may be run as via sudo's -u
option. The second defines a list of groups that can be specified via sudo's -g option. If both
Runas_Lists are specified, the command may be run with any combination of users and groups listed in
their respective Runas_Lists. If only the first is specified, the command may be run as any user in the
list but no -g option may be specified. If the first Runas_List is empty but the second is specified,
the command may be run as the invoking user with the group set to any listed in the Runas_List. If both
Runas_Lists are empty, the command may only be run as the invoking user. If no Runas_Spec is specified
the command may be run as root and no group may be specified.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm—but only as operator. E.g.,
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
Note that while the group portion of the Runas_Spec permits the user to run as command with that group,
it does not force the user to do so. If no group is specified on the command line, the command will run
with the group listed in the target user's password database entry. The following would all be permitted
by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem device file with the dialer
group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
Note that in this example only the group will be set, the command still runs as user tcm. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which case the user may select any
combination of users and groups via the -u and -g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally setting the group to operator or
system.
SELinux_Spec
On systems with SELinux support, sudoers file entries may optionally have an SELinux role and/or type
associated with a command. If a role or type is specified with the command it will override any default
values specified in sudoers. A role or type specified on the command line, however, will supersede the
values in sudoers.
Tag_Spec
A command may have zero or more tags associated with it. There are ten possible tag values: EXEC,
NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, PASSWD,
NOPASSWD, SETENV, and NOSETENV. Once a tag is set on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List,
inherit the tag unless it is overridden by the opposite tag (in other words, PASSWD overrides NOPASSWD
and NOEXEC overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the underlying operating system supports it, the
NOEXEC tag can be used to prevent a dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be
disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the “Preventing shell escapes” section below for more details on how NOEXEC works and whether or
not it will work on your system.
FOLLOW and NOFOLLOW Starting with version 1.8.15, sudoedit will not open a file that is a symbolic link
unless the sudoedit_follow option is enabled. The FOLLOW and NOFOLLOW tags override the value of
sudoedit_follow and can be used to permit (or deny) the editing of symbolic links on a per-command
basis. These tags are only effective for the sudoedit command and are ignored for all other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input option on a per-command basis. For more information,
see the description of log_input in the “SUDOERS OPTIONS” section below.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output option on a per-command basis. For more information,
see the description of log_output in the “SUDOERS OPTIONS” section below.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will be sent when a user runs a command by
overriding the value of the mail_all_cmnds option on a per-command basis. They have no effect when
sudo is run with the -l or -v options. A NOMAIL tag will also override the mail_always and
mail_no_perms options. For more information, see the descriptions of mail_all_cmnds, mail_always, and
mail_no_perms in the “SUDOERS OPTIONS” section below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate him or herself before running a command. This
behavior can be modified via the NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default for
the commands that follow it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be used to reverse
things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine rushmore
without authenticating himself. If we only want ray to be able to run /bin/kill without a password the
entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are in the group specified by the
exempt_group option.
By default, if the NOPASSWD tag is applied to any of the entries for a user on the current host, he or
she will be able to run “sudo -l” without a password. Additionally, a user may only run “sudo -v”
without a password if the NOPASSWD tag is present for all a user's entries that pertain to the current
host. This behavior may be overridden via the verifypw and listpw options.
SETENV and NOSETENV
These tags override the value of the setenv option on a per-command basis. Note that if SETENV has
been set for a command, the user may disable the env_reset option from the command line via the -E
option. Additionally, environment variables set on the command line are not subject to the
restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be
allowed to set variables in this manner. If the command matched is ALL, the SETENV tag is implied for
that command; this default may be overridden by use of the NOSETENV tag.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names and
command line arguments in the sudoers file. Wildcard matching is done via the glob(3) and fnmatch(3)
functions as specified by IEEE Std 1003.1 (“POSIX.1”).
* Matches any set of zero or more characters (including white space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character ‘x’, evaluates to ‘x’. This is used to escape special characters such as:
‘*’, ‘?’, ‘[’, and ‘]’.
Note that these are not regular expressions. Unlike a regular expression there is no way to match one or
more characters within a range.
Character classes may be used if your system's glob(3) and fnmatch(3) functions support them. However,
because the ‘:’ character has special meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
Note that a forward slash (‘/’) will not be matched by wildcards used in the file name portion of the
command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched by wildcards since command
line arguments may contain arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care.
Command line arguments are matched as a single, concatenated string. This mean a wildcard character such
as ‘?’ or ‘*’ will match across word boundaries, which may be unexpected. For example, while a sudoers
entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. In most cases it is better to do command line processing
outside of the sudoers file in a scripting language.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string "" is the only command line argument in the sudoers file entry it means
that command is not allowed to be run with any arguments.
sudoedit Command line arguments to the sudoedit built-in command should always be path names, so a
forward slash (‘/’) will not be matched by a wildcard.
Including other files from within sudoers
It is possible to include other sudoers files from within the sudoers file currently being parsed using
the #include and #includedir directives.
This can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file.
For the sake of this example the site-wide sudoers file will be /etc/sudoers and the per-machine one will
be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers we would use the following
line in /etc/sudoers:
#include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch to
/etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be
processed. Files that are included may themselves include other files. A hard limit of 128 nested
include files is enforced to prevent include file loops.
If the path to the include file is not fully-qualified (does not begin with a ‘/’, it must be located in
the same directory as the sudoers file it was included from. For example, if /etc/sudoers contains the
line:
#include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the %h escape, signifying the short form of the host name. In other
words, if the machine's host name is “xerxes”, then
#include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The #includedir directive can be used to create a sudoers.d directory that the system package manager can
drop sudoers file rules into as part of package installation. For example, given:
#includedir /etc/sudoers.d
sudo will read each file in /etc/sudoers.d, skipping file names that end in ‘~’ or contain a ‘.’
character to avoid causing problems with package manager or editor temporary/backup files. Files are
parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before
/etc/sudoers.d/10_second. Be aware that because the sorting is lexical, not numeric,
/etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second. Using a consistent number of
leading zeroes in the file names can be used to avoid such problems.
Note that unlike files included via #include, visudo will not edit the files in a #includedir directory
unless one of them contains a syntax error. It is still possible to run visudo with the -f flag to edit
the files directly, but this will not catch the redefinition of an alias that is also present in a
different file.
Other special characters and reserved words
The pound sign (‘#’) is used to indicate a comment (unless it is part of a #include directive or unless
it occurs in the context of a user name and is followed by one or more digits, in which case it is
treated as a uid). Both the comment character and any text after it, up to the end of the line, are
ignored.
The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever
one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. You should not try to
define your own alias called ALL as the built-in alias will be used in preference to your own. Please
note that using ALL can be dangerous since in a command context, it allows the user to run any command on
the system.
An exclamation point (‘!’) can be used as a logical not operator in a list or alias as well as in front
of a Cmnd. This allows one to exclude certain values. For the ‘!’ operator to be effective, there must
be something for it to exclude. For example, to match all users except for root one would use:
ALL,!root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is different from a true “negation”
operator.
Note, however, that using a ‘!’ in conjunction with the built-in ALL alias to allow a user to run “all
but a few” commands rarely works as intended (see “SECURITY NOTES” below).
Long lines can be continued with a backslash (‘\’) as the last character on the line.
White space between elements in a list as well as special syntactic characters in a User Specification
(‘=’, ‘:’, ‘(’, ‘)’) is optional.
The following characters must be escaped with a backslash (‘\’) when used as part of a word (e.g. a user
name or host name): ‘!’, ‘=’, ‘:’, ‘,’, ‘(’, ‘)’, ‘\’.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained earlier. A list of all supported
Defaults parameters, grouped by type, are listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to resolve groups of the form %group as long as
there is not also a system group of the same name. Normally, only groups of the form
%:group are passed to the group_plugin. This flag is off by default.
always_set_home If enabled, sudo will set the HOME environment variable to the home directory of the
target user (which is root unless the -u option is used). This effectively means that
the -H option is always implied. Note that by default, HOME will be set to the home
directory of the target user when the env_reset option is enabled, so always_set_home
only has an effect for configurations where either env_reset is disabled or HOME is
present in the env_keep list. This flag is off by default.
authenticate If set, users must authenticate themselves via a password (or other means of
authentication) before they may run commands. This default may be overridden via the
PASSWD and NOPASSWD tags. This flag is on by default.
closefrom_override
If set, the user may use sudo's -C option which overrides the default starting point at
which sudo begins closing open file descriptors. This flag is off by default.
compress_io If set, and sudo is configured to log a command's input or output, the I/O logs will be
compressed using zlib. This flag is on by default when sudo is compiled with zlib
support.
exec_background By default, sudo runs a command as the foreground process as long as sudo itself is
running in the foreground. When the exec_background flag is enabled and the command is
being run in a pty (due to I/O logging or the use_pty flag), the command will be run as
a background process. Attempts to read from the controlling terminal (or to change
terminal settings) will result in the command being suspended with the SIGTTIN signal
(or SIGTTOU in the case of terminal settings). If this happens when sudo is a
foreground process, the command will be granted the controlling terminal and resumed in
the foreground with no user intervention required. The advantage of initially running
the command in the background is that sudo need not read from the terminal unless the
command explicitly requests it. Otherwise, any terminal input must be passed to the
command, whether it has required it or not (the kernel buffers terminals so it is not
possible to tell whether the command really wants the input). This is different from
historic sudo behavior or when the command is not being run in a pty.
For this to work seamlessly, the operating system must support the automatic restarting
of system calls. Unfortunately, not all operating systems do this by default, and even
those that do may have bugs. For example, Mac OS X fails to restart the tcgetattr()
and tcsetattr() system calls (this is a bug in Mac OS X). Furthermore, because this
behavior depends on the command stopping with the SIGTTIN or SIGTTOU signals, programs
that catch these signals and suspend themselves with a different signal (usually
SIGTOP) will not be automatically foregrounded. Some versions of the linux su(1)
command behave this way. This flag is off by default.
This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O
logging is enabled or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the EDITOR or VISUAL environment variables before
falling back on the default editor list. Note that this may create a security hole as
it allows the user to run any arbitrary command as root without logging. A safer
alternative is to place a colon-separated list of editors in the editor variable.
visudo will then only use the EDITOR or VISUAL if they match a value specified in
editor. This flag is on by default.
env_reset If set, sudo will run the command in a minimal environment containing the TERM, PATH,
HOME, MAIL, SHELL, LOGNAME, USER, USERNAME and SUDO_* variables. Any variables in the
caller's environment that match the env_keep and env_check lists are then added,
followed by any variables present in the file specified by the env_file option (if
any). The contents of the env_keep and env_check lists, as modified by global Defaults
parameters in sudoers, are displayed when sudo is run by root with the -V option. If
the secure_path option is set, its value will be used for the PATH environment
variable. This flag is on by default.
fast_glob Normally, sudo uses the glob(3) function to do shell-style globbing when matching path
names. However, since it accesses the file system, glob(3) can take a long time to
complete for some patterns, especially when the pattern references a network file
system that is mounted on demand (auto mounted). The fast_glob option causes sudo to
use the fnmatch(3) function, which does not access the file system to do its matching.
The disadvantage of fast_glob is that it is unable to match relative path names such as
./ls or ../bin/ls. This has security implications when path names that include
globbing characters are used with the negation operator, ‘!’, as such rules can be
trivially bypassed. As such, this option should not be used when the sudoers file
contains rules that contain negated path names which include globbing characters. This
flag is off by default.
fqdn Set this flag if you want to put fully qualified host names in the sudoers file when
the local host name (as returned by the hostname command) does not contain the domain
name. In other words, instead of myhost you would use myhost.mydomain.edu. You may
still use the short form if you wish (and even mix the two). This option is only
effective when the “canonical” host name, as returned by the getaddrinfo() or
gethostbyname() function, is a fully-qualified domain name. This is usually the case
when the system is configured to use DNS for host name resolution.
If the system is configured to use the /etc/hosts file in preference to DNS, the
“canonical” host name may not be fully-qualified. The order that sources are queried
for host name resolution is usually specified in the /etc/nsswitch.conf,
/etc/netsvc.conf, /etc/host.conf, or, in some cases, /etc/resolv.conf file. In the
/etc/hosts file, the first host name of the entry is considered to be the “canonical”
name; subsequent names are aliases that are not used by sudoers. For example, the
following hosts file line for the machine “xyzzy” has the fully-qualified domain name
as the “canonical” host name, and the short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not formatted properly, the fqdn option will not
be effective if it is queried before DNS.
Beware that when using DNS for host name resolution, turning on fqdn requires sudoers
to make DNS lookups which renders sudo unusable if DNS stops working (for example if
the machine is disconnected from the network). Also note that just like with the hosts
file, you must use the “canonical” name as DNS knows it. That is, you may not use a
host alias (CNAME entry) due to performance issues and the fact that there is no way to
get all aliases from DNS.
This flag is on by default.
ignore_dot If set, sudo will ignore "." or "" (both denoting current directory) in the PATH
environment variable; the PATH itself is not modified. This flag is off by default.
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be skipped. This is intended for
Enterprises that wish to prevent the usage of local sudoers files so that only LDAP is
used. This thwarts the efforts of rogue operators who would attempt to add roles to
/etc/sudoers. When this option is present, /etc/sudoers does not even need to exist.
Since this option tells sudo how to behave when no specific LDAP entries have been
matched, this sudoOption is only meaningful for the cn=defaults section. This flag is
off by default.
insults If set, sudo will insult users when they enter an incorrect password. This flag is off
by default.
log_host If set, the host name will be logged in the (non-syslog) sudo log file. This flag is
off by default.
log_input If set, sudo will run the command in a pseudo-tty and log all user input. If the
standard input is not connected to the user's tty, due to I/O redirection or because
the command is part of a pipeline, that input is also captured and stored in a separate
log file. For more information, see the “I/O LOG FILES” section. This flag is off by
default.
log_output If set, sudo will run the command in a pseudo-tty and log all output that is sent to
the screen, similar to the script(1) command. For more information, see the “I/O LOG
FILES” section. This flag is off by default.
log_year If set, the four-digit year will be logged in the (non-syslog) sudo log file. This
flag is off by default.
long_otp_prompt When validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line
prompt is used to make it easier to cut and paste the challenge to a local window.
It's not as pretty as the default but some people find it more convenient. This flag
is off by default.
mail_all_cmnds Send mail to the mailto user every time a user attempts to run a command via sudo (this
includes sudoedit). No mail will be sent if the user runs sudo with the -l or -v
option unless there is an authentication error and the mail_badpass flag is also set.
This flag is off by default.
mail_always Send mail to the mailto user every time a user runs sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo does not enter the correct
password. If the command the user is attempting to run is not permitted by sudoers and
one of the mail_all_cmnds, mail_always, mail_no_host, mail_no_perms or mail_no_user
flags are set, this flag will have no effect. This flag is off by default.
mail_no_host If set, mail will be sent to the mailto user if the invoking user exists in the sudoers
file, but is not allowed to run commands on the current host. This flag is off by
default.
mail_no_perms If set, mail will be sent to the mailto user if the invoking user is allowed to use
sudo but the command they are trying is not listed in their sudoers file entry or is
explicitly denied. This flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if the invoking user is not in the sudoers
file. This flag is on by default.
netgroup_tuple If set, netgroup lookups will be performed using the full netgroup tuple: host name,
user name and domain (if one is set). Historically, sudo only matched the user name
and domain for netgroups used in a User_List and only matched the host name and domain
for netgroups used in a Host_List. This flag is off by default.
noexec If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless
overridden by an EXEC tag. See the description of EXEC and NOEXEC above as well as the
“Preventing shell escapes” section at the end of this manual. This flag is off by
default.
pam_session On systems that use PAM for authentication, sudo will create a new PAM session for the
command to be run in. Disabling pam_session may be needed on older PAM implementations
or on operating systems where opening a PAM session changes the utmp or wtmp files. If
PAM session support is disabled, resource limits may not be updated for the command
being run. If pam_session, pam_setcred, and use_pty are disabled and I/O logging has
not been configured, sudo will execute the command directly instead of running it as a
child process. This flag is on by default.
This setting is only supported by version 1.8.7 or higher.
pam_setcred On systems that use PAM for authentication, sudo will attempt to establish credentials
for the target user by default, if supported by the underlying authentication system.
One example of a credential is a Kerberos ticket. If pam_session, pam_setcred, and
use_pty are disabled and I/O logging has not been configured, sudo will execute the
command directly instead of running it as a child process. This flag is on by default.
This setting is only supported by version 1.8.8 or higher.
passprompt_override
The password prompt specified by passprompt will normally only be used if the password
prompt provided by systems such as PAM matches the string “Password:”. If
passprompt_override is set, passprompt will always be used. This flag is off by
default.
path_info Normally, sudo will tell the user when a command could not be found in their PATH
environment variable. Some sites may wish to disable this as it could be used to
gather information on the location of executables that the normal user does not have
access to. The disadvantage is that if the executable is simply not in the user's
PATH, sudo will tell the user that they are not allowed to run it, which can be
confusing. This flag is on by default.
preserve_groups By default, sudo will initialize the group vector to the list of groups the target user
is in. When preserve_groups is set, the user's existing group vector is left
unaltered. The real and effective group IDs, however, are still set to match the
target user. This flag is off by default.
pwfeedback By default, sudo reads the password like most other Unix programs, by turning off echo
until the user hits the return (or enter) key. Some users become confused by this as
it appears to them that sudo has hung at this point. When pwfeedback is set, sudo will
provide visual feedback when the user presses a key. Note that this does have a
security impact as an onlooker may be able to determine the length of the password
being entered. This flag is off by default.
requiretty If set, sudo will only run when the user is logged in to a real tty. When this flag is
set, sudo can only be run from a login session and not via other means such as cron(8)
or cgi-bin scripts. This flag is off by default.
root_sudo If set, root is allowed to run sudo too. Disabling this prevents users from “chaining”
sudo commands to get a root shell by doing something like “sudo sudo /bin/sh”. Note,
however, that turning off root_sudo will also prevent root from running sudoedit.
Disabling root_sudo provides no real additional security; it exists purely for
historical reasons. This flag is on by default.
rootpw If set, sudo will prompt for the root password instead of the password of the invoking
user when running a command or editing a file. This flag is off by default.
runaspw If set, sudo will prompt for the password of the user defined by the runas_default
option (defaults to root) instead of the password of the invoking user when running a
command or editing a file. This flag is off by default.
set_home If enabled and sudo is invoked with the -s option the HOME environment variable will be
set to the home directory of the target user (which is root unless the -u option is
used). This effectively makes the -s option imply -H. Note that HOME is already set
when the env_reset option is enabled, so set_home is only effective for configurations
where either env_reset is disabled or HOME is present in the env_keep list. This flag
is off by default.
set_logname Normally, sudo will set the LOGNAME, USER and USERNAME environment variables to the
name of the target user (usually root unless the -u option is given). However, since
some programs (including the RCS revision control system) use LOGNAME to determine the
real identity of the user, it may be desirable to change this behavior. This can be
done by negating the set_logname option. Note that set_logname will have no effect if
the env_reset option has not been disabled and the env_keep list contains LOGNAME, USER
or USERNAME. This flag is on by default.
set_utmp When enabled, sudo will create an entry in the utmp (or utmpx) file when a pseudo-tty
is allocated. A pseudo-tty is allocated by sudo when the log_input, log_output or
use_pty flags are enabled. By default, the new entry will be a copy of the user's
existing utmp entry (if any), with the tty, time, type and pid fields updated. This
flag is on by default.
setenv Allow the user to disable the env_reset option from the command line via the -E option.
Additionally, environment variables set via the command line are not subject to the
restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted
users should be allowed to set variables in this manner. This flag is off by default.
shell_noargs If set and sudo is invoked with no arguments it acts as if the -s option had been
given. That is, it runs a shell as root (the shell is determined by the SHELL
environment variable if it is set, falling back on the shell listed in the invoking
user's /etc/passwd entry if not). This flag is off by default.
stay_setuid Normally, when sudo executes a command the real and effective UIDs are set to the
target user (root by default). This option changes that behavior such that the real
UID is left as the invoking user's UID. In other words, this makes sudo act as a
setuid wrapper. This can be useful on systems that disable some potentially dangerous
functionality when a program is run setuid. This option is only effective on systems
that support either the setreuid(2) or setresuid(2) system call. This flag is off by
default.
sudoedit_checkdir
If set, sudoedit will check all directory components of the path to be edited for
writability by the invoking user. Symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a writable directory.
These restrictions are not enforced when sudoedit is run by root. On some systems, if
all directory components of the path to be edited are not readable by the target user,
sudoedit will be unable to edit the file. This flag is on by default.
This setting was first introduced in version 1.8.15 but initially suffered from a race
condition. The check for symbolic links in writable intermediate directories was added
in version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic links when opening files. The
sudoedit_follow option can be enabled to allow sudoedit to open symbolic links. It may
be overridden on a per-command basis by the FOLLOW and NOFOLLOW tags. This flag is off
by default.
This setting is only supported by version 1.8.15 or higher.
targetpw If set, sudo will prompt for the password of the user specified by the -u option
(defaults to root) instead of the password of the invoking user when running a command
or editing a file. Note that this flag precludes the use of a uid not listed in the
passwd database as an argument to the -u option. This flag is off by default.
tty_tickets If set, users must authenticate on a per-tty basis. With this flag enabled, sudo will
use a separate record in the time stamp file for each tty. If disabled, a single
record is used for all login sessions. This flag is on by default.
umask_override If set, sudo will set the umask as specified in the sudoers file without modification.
This makes it possible to specify a umask in the sudoers file that is more permissive
than the user's own umask and matches historical behavior. If umask_override is not
set, sudo will set the umask to be the union of the user's umask and what is specified
in sudoers. This flag is off by default.
use_netgroups If set, netgroups (prefixed with ‘+’), may be used in place of a user or host. For
LDAP-based sudoers, netgroup support requires an expensive substring match on the
server unless the NETGROUP_BASE directive is present in the /etc/sudo-ldap.conf file.
If netgroups are not needed, this option can be disabled to reduce the load on the LDAP
server. This flag is on by default.
use_pty If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone.
A malicious program run under sudo could conceivably fork a background process that
retains to the user's terminal device after the main program has finished executing.
Use of this option will make that impossible. This flag is off by default.
utmp_runas If set, sudo will store the name of the runas user when updating the utmp (or utmpx)
file. By default, sudo stores the name of the invoking user. This flag is off by
default.
visiblepw By default, sudo will refuse to run if the user must enter a password but it is not
possible to disable echo on the terminal. If the visiblepw flag is set, sudo will
prompt for a password even when it would be visible on the screen. This makes it
possible to run things like “ssh somehost sudo ls” since by default, ssh(1) does not
allocate a tty when running a command. This flag is off by default.
Integers:
closefrom Before it executes a command, sudo will close all open file descriptors other than
standard input, standard output and standard error (ie: file descriptors 0-2). The
closefrom option can be used to specify a different file descriptor at which to start
closing. The default is 3.
maxseq The maximum sequence number that will be substituted for the “%{seq}” escape in the I/O
log file (see the iolog_dir description above for more information). While the value
substituted for “%{seq}” is in base 36, maxseq itself should be expressed in decimal.
Values larger than 2176782336 (which corresponds to the base 36 sequence number
“ZZZZZZ”) will be silently truncated to 2176782336. The default value is 2176782336.
Once the local sequence number reaches the value of maxseq, it will “roll over” to
zero, after which sudoers will truncate and re-use any existing I/O log path names.
This setting is only supported by version 1.8.7 or higher.
passwd_tries The number of tries a user gets to enter his/her password before sudo logs the failure
and exits. The default is 3.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log. This value is used to decide when to
wrap lines for nicer log files. This has no effect on the syslog log file, only the
file log. The default is 80 (use 0 or negate the option to disable word wrap).
passwd_timeout Number of minutes before the sudo password prompt times out, or 0 for no timeout. The
timeout may include a fractional component if minute granularity is insufficient, for
example 2.5. The default is 0.
timestamp_timeout
Number of minutes that can elapse before sudo will ask for a passwd again. The timeout
may include a fractional component if minute granularity is insufficient, for example
2.5. The default is 15. Set this to 0 to always prompt for a password. If set to a
value less than 0 the user's time stamp will never expire. This can be used to allow
users to create or delete their own time stamps via “sudo -v” and “sudo -k”
respectively.
umask Umask to use when running the command. Negate this option or set it to 0777 to
preserve the user's umask. The actual umask that is used will be the union of the
user's umask and the value of the umask option, which defaults to 0022. This
guarantees that sudo never lowers the umask when running a command. Note: on systems
that use PAM, the default PAM configuration may specify its own umask which will
override the value set in sudoers.
Strings:
badpass_message Message that is displayed if a user enters an incorrect password. The default is
Sorry, try again. unless insults are enabled.
editor A colon (‘:’) separated list of editors allowed to be used with visudo. visudo will
choose the editor that matches the user's EDITOR environment variable if possible, or
the first editor in the list that exists and is executable. The default is
/usr/bin/editor.
iolog_dir The top-level directory to use when constructing the path name for the input/output log
directory. Only used if the log_input or log_output options are enabled or when the
LOG_INPUT or LOG_OUTPUT tags are present for a command. The session sequence number,
if any, is stored in the directory. The default is /var/log/sudo-io.
The following percent (‘%’) escape sequences are supported:
%{seq}
expanded to a monotonically increasing base-36 sequence number, such as 0100A5,
where every two digits are used to form a new directory, e.g. 01/00/A5
%{user}
expanded to the invoking user's login name
%{group}
expanded to the name of the invoking user's real group ID
%{runas_user}
expanded to the login name of the user the command will be run as (e.g. root)
%{runas_group}
expanded to the group name of the user the command will be run as (e.g. wheel)
%{hostname}
expanded to the local host name without the domain name
%{command}
expanded to the base name of the command being run
In addition, any escape sequences supported by the system's strftime(3) function will
be expanded.
To include a literal ‘%’ character, the string ‘%%’ should be used.
iolog_file The path name, relative to iolog_dir, in which to store input/output logs when the
log_input or log_output options are enabled or when the LOG_INPUT or LOG_OUTPUT tags
are present for a command. Note that iolog_file may contain directory components. The
default is “%{seq}”.
See the iolog_dir option above for a list of supported percent (‘%’) escape sequences.
In addition to the escape sequences, path names that end in six or more Xs will have
the Xs replaced with a unique combination of digits and letters, similar to the
mktemp(3) function.
If the path created by concatenating iolog_dir and iolog_file already exists, the
existing I/O log file will be truncated and overwritten unless iolog_file ends in six
or more Xs.
lecture_status_dir
The directory in which sudo stores per-user lecture status files. Once a user has
received the lecture, a zero-length file is created in this directory so that sudo will
not lecture the user again. This directory should not be cleared when the system
reboots. The default is /var/lib/sudo/lectured.
mailsub Subject of the mail sent to the mailto user. The escape %h will expand to the host
name of the machine. Default is “*** SECURITY information for %h ***”.
noexec_file As of sudo version 1.8.1 this option is no longer supported. The path to the noexec
file should now be set in the sudo.conf(5) file.
pam_login_service
On systems that use PAM for authentication, this is the service name used when the -i
option is specified. The default value is “sudo”. See the description of pam_service
for more information.
This setting is only supported by version 1.8.8 or higher.
pam_service On systems that use PAM for authentication, the service name specifies the PAM policy
to apply. This usually corresponds to an entry in the pam.conf file or a file in the
/etc/pam.d directory. The default value is “sudo”.
This setting is only supported by version 1.8.8 or higher.
passprompt The default prompt to use when asking for a password; can be overridden via the -p
option or the SUDO_PROMPT environment variable. The following percent (‘%’) escape
sequences are supported:
%H expanded to the local host name including the domain name (only if the machine's
host name is fully qualified or the fqdn option is set)
%h expanded to the local host name without the domain name
%p expanded to the user whose password is being asked for (respects the rootpw,
targetpw and runaspw flags in sudoers)
%U expanded to the login name of the user the command will be run as (defaults to
root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into a single % character
The default value is “[sudo] password for %p:”.
role The default SELinux role to use when constructing a new security context to run the
command. The default role may be overridden on a per-command basis in the sudoers file
or via command line options. This option is only available when sudo is built with
SELinux support.
runas_default The default user to run commands as if the -u option is not specified on the command
line. This defaults to root.
syslog_badpri Syslog priority to use when user authenticates unsuccessfully. Defaults to alert.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info,
notice, and warning.
syslog_goodpri Syslog priority to use when user authenticates successfully. Defaults to notice.
See syslog_badpri for the list of supported syslog priorities.
sudoers_locale Locale to use when parsing the sudoers file, logging commands, and sending email. Note
that changing the locale may affect how sudoers is interpreted. Defaults to “C”.
timestampdir The directory in which sudo stores its time stamp files. This directory should be
cleared when the system reboots. The default is /var/run/sudo/ts.
timestampowner The owner of the lecture status directory, time stamp directory and all files stored
therein. The default is root.
type The default SELinux type to use when constructing a new security context to run the
command. The default type may be overridden on a per-command basis in the sudoers file
or via command line options. This option is only available when sudo is built with
SELinux support.
Strings that can be used in a boolean context:
env_file The env_file option specifies the fully qualified path to a file containing variables to be
set in the environment of the program being run. Entries in this file should either be of
the form “VARIABLE=value” or “export VARIABLE=value”. The value may optionally be
surrounded by single or double quotes. Variables in this file are subject to other sudo
environment settings such as env_keep and env_check.
exempt_group Users in this group are exempt from password and PATH requirements. The group name
specified should not include a % prefix. This is not set by default.
group_plugin A string containing a sudoers group plugin with optional arguments. The string should
consist of the plugin path, either fully-qualified or relative to the /usr/lib/sudo
directory, followed by any configuration arguments the plugin requires. These arguments
(if any) will be passed to the plugin's initialization function. If arguments are present,
the string must be enclosed in double quotes ("").
For more information see GROUP PROVIDER PLUGINS.
lecture This option controls when a short lecture will be printed along with the password prompt.
It has the following possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied. Negating the option results in a
value of never being used. The default value is never.
lecture_file Path to a file containing an alternate sudo lecture that will be used in place of the
standard lecture if the named file exists. By default, sudo uses a built-in lecture.
listpw This option controls when a password will be required when a user runs sudo with the -l
option. It has the following possible values:
all All the user's sudoers file entries for the current host must have the NOPASSWD
flag set to avoid entering a password.
always The user must always enter a password to use the -l option.
any At least one of the user's sudoers file entries for the current host must have
the NOPASSWD flag set to avoid entering a password.
never The user need never enter a password to use the -l option.
If no value is specified, a value of any is implied. Negating the option results in a
value of never being used. The default value is any.
logfile Path to the sudo log file (not the syslog log file). Setting a path turns on logging to a
file; negating this option turns it off. By default, sudo logs via syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail. Defaults to the path to sendmail found at
configure time.
mailfrom Address to use for the “from” address when sending warning and error mail. The address
should be enclosed in double quotes ("") to protect against sudo interpreting the @ sign.
Defaults to the name of the user running sudo.
mailto Address to send warning and error mail to. The address should be enclosed in double quotes
("") to protect against sudo interpreting the @ sign. Defaults to root.
secure_path Path used for every command run from sudo. If you don't trust the people running sudo to
have a sane PATH environment variable you may want to use this. Another use is if you want
to have the “root path” be separate from the “user path”. Users in the group specified by
the exempt_group option are not affected by secure_path. This option is not set by
default.
syslog Syslog facility if syslog is being used for logging (negate to disable syslog logging).
Defaults to authpriv.
The following syslog facilities are supported: authpriv (if your OS supports it), auth,
daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
verifypw This option controls when a password will be required when a user runs sudo with the -v
option. It has the following possible values:
all All the user's sudoers file entries for the current host must have the NOPASSWD
flag set to avoid entering a password.
always The user must always enter a password to use the -v option.
any At least one of the user's sudoers file entries for the current host must have the
NOPASSWD flag set to avoid entering a password.
never The user need never enter a password to use the -v option.
If no value is specified, a value of all is implied. Negating the option results in a
value of never being used. The default value is all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the user's environment unless they are
considered “safe”. For all variables except TZ, “safe” means that the variable's value
does not contain any ‘%’ or ‘/’ characters. This can be used to guard against printf-
style format vulnerabilities in poorly-written programs. The TZ variable is considered
unsafe if any of the following are true:
• It consists of a fully-qualified path name, optionally prefixed with a colon (‘:’),
that does not match the location of the zoneinfo directory.
• It contains a .. path element.
• It contains white space or non-printable characters.
• It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-separated list or a single value without
double-quotes. The list can be replaced, added to, deleted from, or disabled by using
the =, +=, -=, and ! operators respectively. Regardless of whether the env_reset
option is enabled or disabled, variables specified by env_check will be preserved in
the environment if they pass the aforementioned check. The global list of environment
variables to check is displayed when sudo is run by root with the -V option.
env_delete Environment variables to be removed from the user's environment when the env_reset
option is not in effect. The argument may be a double-quoted, space-separated list or
a single value without double-quotes. The list can be replaced, added to, deleted
from, or disabled by using the =, +=, -=, and ! operators respectively. The global
list of environment variables to remove is displayed when sudo is run by root with the
-V option. Note that many operating systems will remove potentially dangerous
variables from the environment of any setuid process (such as sudo).
env_keep Environment variables to be preserved in the user's environment when the env_reset
option is in effect. This allows fine-grained control over the environment
sudo-spawned processes will receive. The argument may be a double-quoted, space-
separated list or a single value without double-quotes. The list can be replaced,
added to, deleted from, or disabled by using the =, +=, -=, and ! operators
respectively. The global list of variables to keep is displayed when sudo is run by
root with the -V option.
GROUP PROVIDER PLUGINS
The sudoers plugin supports its own plugin interface to allow non-Unix group lookups which can query a
group source other than the standard Unix group database. This can be used to implement support for the
nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin Defaults setting. The argument to group_plugin
should consist of the plugin path, either fully-qualified or relative to the /usr/lib/sudo directory,
followed by any configuration options the plugin requires. These options (if specified) will be passed
to the plugin's initialization function. If options are present, the string must be enclosed in double
quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file that uses the same syntax as the
/etc/group file. The path to the group file should be specified as an option to the plugin.
For example, if the group file to be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the standard C library functions getgrnam()
and getgrid(). This plugin can be used in instances where the user belongs to groups not
present in the user's supplemental group vector. This plugin takes no options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(8).
LOG FORMAT
sudoers can log events using either syslog(3) or a simple log file. The log format is almost identical
in both cases.
Accepted command log entries
Commands that sudo runs are logged using the following format (split into multiple lines for
readability):
date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is in the format “MMM, DD, HH:MM:SS”. If
logging via syslog(3), the actual date format is controlled by the syslog daemon. If
logging to a file and the log_year option is enabled, the date will also include the year.
hostname The name of the host sudo was run on. This field is only present when logging via
syslog(3).
progname The name of the program, usually sudo or sudoedit. This field is only present when logging
via syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g. “console”, “tty01”, or “pts/0”) sudo was run on, or
“unknown” if there was no terminal present.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was specified on the command line.
logid An I/O log identifier that can be used to replay the command's output. This is only
present when the log_input or log_output option is enabled.
env_vars A list of environment variables specified on the command line, if specified.
command The actual command that was executed.
Messages are logged using the locale specified by sudoers_locale, which defaults to the “C” locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the denial will follow the user name.
Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they are not allowed to run the specified
command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The actual number of tries will vary based on
the number of failed attempts and the value of the passwd_tries option.
a password is required
sudo's -n option was specified but a password was required.
sorry, you are not allowed to set the following environment variables
The user specified environment variables on the command line that were not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most cases, send a message to the administrator
via email. Possible errors include:
parse error in /etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In some cases, the actual error may be
one line above or below the line number listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults settings. This does not prevent sudo from
running, but the sudoers file should be checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the timestampowner setting, could not be found in the
password database.
unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can happen when the sudoers file is located on
a remote file system that maps user ID 0 to a different value. Normally, sudoers tries to open the
sudoers file using group permissions to avoid this problem. Consider either changing the ownership of
/etc/sudoers or adding an argument like “sudoers_uid=N” (where ‘N’ is the user ID that owns the sudoers
file) to the end of the sudoers Plugin line in the sudo.conf(5) file.
unable to stat /etc/sudoers
The /etc/sudoers file is missing.
/etc/sudoers is not a regular file
The /etc/sudoers file exists but is not a regular file or symbolic link.
/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the sudoers file owner, please add
“sudoers_uid=N” (where ‘N’ is the user ID that owns the sudoers file) to the sudoers Plugin line in the
sudo.conf(5) file.
/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to it. The sudoers file must not be
world-writable, the default file mode is 0440 (readable by owner and group, writable by none). The
default mode may be changed via the “sudoers_mode” option to the sudoers Plugin line in the
sudo.conf(5) file.
/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to change the sudoers file group
ownership, please add “sudoers_gid=N” (where ‘N’ is the group ID that owns the sudoers file) to the
sudoers Plugin line in the sudo.conf(5) file.
unable to open /var/run/sudo/ts/username
sudoers was unable to read or create the user's time stamp file. This can happen when timestampowner
is set to a user other than root and the mode on /var/run/sudo is not searchable by group or other.
The default mode for /var/run/sudo is 0711.
unable to write to /var/run/sudo/ts/username
sudoers was unable to write to the user's time stamp file.
/var/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than timestampowner. This can occur when the value
of timestampowner has been changed. sudoers will ignore the time stamp directory until the owner is
corrected.
/var/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable only by timestampowner. The default
mode for the time stamp directory is 0700. sudoers will ignore the time stamp directory until the mode
is corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by
the syslog daemon, not sudoers itself. As such, they may vary in format on different systems.
On most systems, syslog(3) has a relatively small log buffer. To prevent the command line arguments from
being truncated, sudoers will split up log messages that are larger than 960 characters (not including
the date, hostname, and the string “sudo”). When a message is split, additional parts will include the
string “(command continued)” after the user name and before the continued command line arguments.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a
file, sudoers uses a format similar to syslog(3), with a few important differences:
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 use grep(1) on the log files. If the loglinelen option is set to 0
(or negated with a ‘!’), word wrap will be disabled.
I/O LOG FILES
When I/O logging is enabled, sudo will run the command in a pseudo-tty and log all user input and/or
output. I/O is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default)
using a unique session ID that is included in the sudo log line, prefixed with “TSID=”. The iolog_file
option may be used to control the format of the session ID.
Each I/O log is stored in a separate directory that contains the following files:
log a text file containing the time the command was run, the name of the user who ran sudo, the
name of the target user, the name of the target group (optional), the terminal that sudo was
run from, the number of rows and columns of the terminal, the working directory the command was
run from and the path name of the command itself (with arguments if present)
timing a log of the amount of time between, and the number of bytes in, each I/O log entry (used for
session playback)
ttyin input from the user's tty (what the user types)
stdin input from a pipe or file
ttyout output from the pseudo-tty (what the command writes to the screen)
stdout standard output to a pipe or redirected to a file
stderr standard error to a pipe or redirected to a file
All files other than log are compressed in gzip format unless the compress_io option has been disabled.
Due to buffering, the I/O log data will not be complete until the sudo command has completed. The output
portion of an I/O log file can be viewed with the sudoreplay(8) utility, which can also be used to list
or search the available logs.
Note that user input may contain sensitive information such as passwords (even if they are not echoed to
the screen), which will be stored in the log file unencrypted. In most cases, logging the command output
via log_output or LOG_OUTPUT is all that is required.
Since each session's I/O logs are stored in a separate directory, traditional log rotation utilities
cannot be used to limit the number of I/O logs. The simplest way to limit the number of I/O is by
setting the maxseq option to the maximum number of logs you wish to store. Once the I/O log sequence
number reaches maxseq, it will be reset to zero and sudoers will truncate and re-use any existing I/O
logs.
FILES
/etc/sudo.conf Sudo front end configuration
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/var/run/sudo/ts Directory containing time stamps for the sudoers security policy
/var/lib/sudo/lectured Directory containing lecture status files for the sudoers security policy
/etc/environment Initial environment for -i mode on AIX and Linux systems
EXAMPLES
Below are example sudoers file entries. Admittedly, some of these are a bit contrived. First, we allow
a few environment variables to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Note that other programs use HOME to find
# configuration files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBMASTERS = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to log via syslog(3) using the
auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user
millert need not give a password, and we don't want to reset the LOGNAME, USER or USERNAME environment
variables when running commands as root. Additionally, on the machines in the SERVERS Host_Alias, we
keep an additional local log file and make sure we log the year in each log line since the log entries
will be kept around for several years. Lastly, we disable shell escapes for the commands in the PAGERS
Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less). Note that this will not effectively constrain
users with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating
themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any command on any host but they must authenticate
themselves first (since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks 128.138.243.0,
128.138.204.0, and 128.138.242.0). Of those networks, only 128.138.204.0 has an explicit netmask (in
CIDR notation) indicating it is a class C network. For the other networks in CSNETS, the local machine's
netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here, those are commands related to
backups, killing processes, the printing system, shutting down the system, and any commands in the
directory /usr/oper/bin/. Note that one command in the DUMPS Cmnd_Alias includes a sha224 digest,
/home/operator/bin/start_backups. This is because the directory containing the script is writable by the
operator user. If the script is modified (resulting in a digest mismatch) it will no longer be possible
to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves with any group in the ADMINGRP
Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on the HPPA machines. Because
command line arguments are matched as a single, concatenated string, the ‘*’ wildcard will match multiple
words. This example assumes that passwd(1) does not take multiple user names on the command line. Note
that on GNU systems, options to passwd(1) may be specified after the user argument. As a result, this
rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user listed in the OP Runas_Alias
(root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo knows that “biglab” is a
netgroup due to the ‘+’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so
they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias (oracle or sybase) without giving a
password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is not allowed to specify any
options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the SERVERS Host_Alias (master, mail,
www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in the directory /usr/bin/ except
for those commands belonging to the SU and SHELLS Cmnd_Aliases. While not specifically mentioned in the
rule, the commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS User_Alias (will, wendy, and wim), may run any command as
user www (which owns the web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus, hercules)
without entering a password. This is a bit tedious for users to type, so it is a prime candidate for
encapsulating in a shell script.
SECURITY NOTES
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL using the ‘!’ operator. A user can
trivially circumvent this by copying the desired command to a different name and then executing that.
For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or SHELLS since he can simply copy
those commands to a different name, or use a shell escape from an editor or other program. Therefore,
these kind of restrictions should be considered advisory at best (and reinforced by policy).
In general, if a user has sudo ALL there is nothing to prevent them from creating their own program that
gives them a root shell (or making their own copy of a shell) regardless of any ‘!’ elements in the user
specification.
Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably negate commands where the path name
includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3) function cannot
resolve relative paths. While this is typically only an inconvenience for rules that grant privileges,
it can result in a security issue for rules that subtract or revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run /usr/bin/passwd root if fast_glob is enabled by changing to /usr/bin and running
./passwd root instead.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever it pleases, including run other
programs. This can be a security issue since it is not uncommon for a program to allow shell escapes,
which lets a user bypass sudo's access control and logging. Common programs that permit shell escapes
include shells (obviously), editors, paginators, mail and terminal programs.
There are two basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user to run arbitrary commands. Many
editors have a restricted mode where shell escapes are disabled, though sudoedit is a better
solution to running editors via sudo. Due to the large number of programs that offer shell
escapes, restricting users to the set of programs that do not is often unworkable.
noexec Many systems that support shared libraries have the ability to override default library
functions by pointing an environment variable (usually LD_PRELOAD) to an alternate shared
library. On such systems, sudo's noexec functionality can be used to prevent a program run by
sudo from executing any other programs. Note, however, that this applies only to native
dynamically-linked executables. Statically-linked executables and foreign executables running
under binary emulation are not affected.
The noexec feature is known to work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X,
HP-UX 11.x and AIX 5.3 and above. It should be supported on most operating systems that
support the LD_PRELOAD environment variable. Check your operating system's manual pages for
the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if LD_PRELOAD
is supported.
To enable noexec for a command, use the NOEXEC tag as documented in the User Specification
section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will
prevent those two commands from executing other commands (such as a shell). If you are unsure
whether or not your system is capable of supporting noexec you can always just try it out and
check whether shell escapes work when noexec is enabled.
Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many
potentially hazardous operations (such as changing or overwriting files) that could lead to unintended
privilege escalation. In the specific case of an editor, a safer approach is to give the user permission
to run sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users to securely edit files with the editor of
their choice. As sudoedit is a built-in command, it must be specified in the sudoers file without a
leading path. However, it may take command line arguments just as a normal command does. Wildcards used
in sudoedit command line arguments are expected to be path names, so a forward slash (‘/’) will not be
matched by a wildcard.
Unlike other sudo commands, the editor is run with the permissions of the invoking user and with the
environment unmodified. More information may be found in the description of the -e option in sudo(8).
For example, to allow user operator to edit the “message of the day” file:
operator sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of /etc/motd. After the file has
been edited, /etc/motd will be updated with the contents of the temporary copy.
Users should never be granted sudoedit permission to edit a file that resides in a directory the user has
write access to, either directly or via a wildcard. If the user has write access to the directory it is
possible to replace the legitimate file with a link to another file, allowing the editing of arbitrary
files. To prevent this, starting with version 1.8.16, symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a writable directory unless the
sudoedit_checkdir option has been disabled or the invoking user is root. Additionally, in version 1.8.15
and higher, sudoedit will refuse to open a symbolic link unless either the sudoedit_follow option is
enabled or the sudoedit command is prefixed with the FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory (/var/run/sudo/ts by default) and ignore the
directory's contents if it is not owned by root or if it is writable by a user other than root. Older
versions of sudo stored time stamp files in /tmp; this is no longer recommended as it may be possible for
a user to create the time stamp themselves on systems that allow unprivileged users to change the
ownership of files they create.
While the time stamp directory should be cleared at reboot time, not all systems contain a /var/run
directory. To avoid potential problems, sudoers will ignore time stamp files that date from before the
machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow unprivileged users to change the system clock.
Since sudoers relies on the system clock for time stamp validation, it may be possible on such systems
for a user to run sudo for longer than timestamp_timeout by setting the clock back. To combat this,
sudoers uses a monotonic clock (which never moves backwards) for its time stamps if the system supports
it.
sudoers will not honor time stamps set far in the future. Time stamps with a date greater than
current_time + 2 * TIMEOUT will be ignored and sudoers will log and complain.
Since time stamp files live in the file system, they can outlive a user's login session. As a result, a
user may be able to login, run a command with sudo after authenticating, logout, login again, and run
sudo without authenticating so long as the record's time stamp is within 15 minutes (or whatever value
the timeout is set to in the sudoers file). When the tty_tickets option is enabled, the time stamp
record includes the device number of the terminal the user authenticated with. This provides per-tty
granularity but time stamp records still may outlive the user's session. The time stamp record also
includes the session ID of the process that last authenticated. This prevents processes in different
terminal sessions from using the same time stamp record. It also helps reduce the chance that a user
will be able to run sudo without entering a password when logging out and back in again on the same
terminal.
DEBUGGING
Versions 1.8.4 and higher of the sudoers plugin support a flexible debugging framework that can help
track down what the plugin is doing internally if there is a problem. This can be configured in the
sudo.conf(5) file.
The sudoers plugin uses the same debug flag format as the sudo front-end: subsystem@priority.
The priorities used by sudoers, in order of decreasing severity, are: crit, err, warn, notice, diag,
info, trace and debug. Each priority, when specified, also includes all priorities higher than it. For
example, a priority of notice would include debug messages logged at notice and higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts and netgroups in the sudoers file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-tty related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudo /var/log/sudo_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
SEE ALSO
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudoers.ldap(5), sudo(8),
sudo_plugin(8), visudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution (https://www.sudo.ws/contributors.html) for an
exhaustive list of people who have contributed to sudo.
CAVEATS
The sudoers file should always be edited by the visudo command which locks the file and does grammatical
checking. It is imperative that the sudoers file be free of syntax errors since sudo will not run with a
syntactically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you store fully qualified host name in the
netgroup (as is usually the case), you either need to have the machine's host name be fully qualified as
returned by the hostname command or use the fqdn option in sudoers.
BUGS
If you feel you have found a bug in sudo, please submit a bug report at https://bugzilla.sudo.ws/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the
LICENSE file distributed with sudo or https://www.sudo.ws/license.html for complete details.
Sudo 1.8.16 January 20, 2016 SUDOERS(5)