Provided by: sudo_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/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.