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