The sudoers policy module 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
Authentication and Logging
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 mail will not be sent if an unauthorized user tries to run
sudo with the -l or -v option. This allows users to determine for
themselves whether or not they are allowed to use sudo.
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 lookup is still done for root, not the user
specified by SUDO_USER.
sudoers uses time stamp files for credential caching. Once a user has
been authenticated, a time stamp is updated and 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 tty-based
time stamp which means that there is a separate time stamp for each of
a user's login sessions. The tty_tickets option can be disabled to
force the use of a single time stamp for all of a user's sessions.
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
sudoers also supports logging a command's input and output streams.
I/O logging is not on by default but can be enabled using the log_input
and log_output Defaults flags as well as the LOG_INPUT and LOG_OUTPUT
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. Since it is not possible to blacklist all
potentially dangerous environment variables, use of the default
env_reset behavior is encouraged.
In all cases, environment variables with a value beginning with () are
removed as they could be interpreted as bash functions. The list of
environment variables that sudo allows or denies is contained in the
output of sudo -V when run as root.
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 Linux and AIX systems the contents of /etc/environment are also
included. All other environment variables are removed.
SUDOERS FILE FORMAT
The sudoers file is composed of two types of entries: aliases
(basically variables) and user specifications (which specify who may
When multiple entries match for a user, they are applied in order.
Where there are multiple matches, the last match is used (which is not
necessarily the most specific match).
The sudoers grammar will be described below in Extended Backus-Naur
Form (EBNF). Don't despair if you don't know what EBNF is; it is
fairly simple, and the definitions below are annotated.
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.
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
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 |
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.
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
o Group SID: "S-1-2-34-5678901234-5678901234-5678901234-567"
Note that quotes around group names are optional. Unquoted strings
must use a backslash (\) to escape spaces and special characters. See
"Other special characters and reserved words" for a list of characters
that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
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 |
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. If you do not
specify a netmask along with the network number, sudo will query each
of the local host's network interfaces and, if the network number
corresponds to one of the hosts's network interfaces, the corresponding
netmask will be used. The netmask may be specified either in standard
IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or
CIDR notation (number of bits, e.g. 24 or 64). A host name may include
shell-style wildcards (see the Wildcards section below), but unless the
host name command on your machine returns the fully qualified host
name, you'll need to use the fqdn option for wildcards to be useful.
Note sudo only inspects actual network interfaces; this means that IP
address 127.0.0.1 (localhost) will never match. Also, the host name
"localhost" will only match if that is the actual host name, which is
usually only the case for non-networked systems.
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
include shell-style wildcards (see the Wildcards section below). A
simple file name allows the user to run the command with any arguments
he/she wishes. However, you may also specify command line arguments
(including wildcards). Alternately, you can specify "" to indicate
that the command may only be run without command line arguments. A
directory is a fully qualified path name ending in a '/'. When you
specify a directory in a Cmnd_List, the user will be able to run any
file within that directory (but not in any subdirectories therein).
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 special command "sudoedit" is used
to permit a user to run sudo with the -e option (or as sudoedit). It
may take command line arguments just as a normal command does.
Certain configuration options may be changed from their default values
at runtime via one or more Default_Entry lines. These may affect all
users on any host, all users on a specific host, a specific user, a
specific command, or commands being run as a specific user. Note that
per-command entries may not include command line arguments. If you
need to specify arguments, define a Cmnd_Alias and reference that
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 |
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.
Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |
'SETENV:' | 'NOSETENV:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' |
'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')
A user specification determines which commands a user may run (and as
what user) on specified hosts. By default, commands are run as root,
but this can be changed on a per-command basis.
The basic structure of a user specification is `who where = (as_whom)
what'. Let's break that down into its constituent parts:
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 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, \
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \
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.
A command may have zero or more tags associated with it. There are
eight possible tag values, NOPASSWD, PASSWD, NOEXEC, EXEC, SETENV,
NOSETENV, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT and NOLOG_OUTPUT. Once a
tag is set on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit
the tag unless it is overridden by the opposite tag (i.e.: PASSWD
overrides NOPASSWD and NOEXEC overrides EXEC).
NOPASSWD and PASSWD
By default, sudo requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
NOPASSWD tag. 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
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.
NOEXEC and EXEC
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.
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.
sudo allows shell-style wildcards (aka meta or glob characters) to be
used in host names, path names and command line arguments in the
sudoers file. Wildcard matching is done via the POSIX glob(3) and
fnmatch(3) routines. Note that these are not regular expressions.
* Matches any set of zero or more characters.
? Matches any single character.
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character "x", evaluates to "x". This is used to
escape special characters such as: "*", "?", "[", and "}".
POSIX character classes may also be used if your system's glob(3) and
fnmatch(3) functions support them. However, because the ':' character
has special meaning in sudoers, it must be escaped. For example:
Would match any file name beginning with a letter.
Note that a forward slash ('/') will not be matched by wildcards used
in the path name. When matching the command line arguments, however, a
slash does get matched by wildcards. This is to make a path like:
It is possible to include other sudoers files from within the sudoers
file currently being parsed using the #include and #includedir
This can be used, for example, to keep a site-wide sudoers file in
addition to a local, per-machine file. For the sake of this example
the site-wide sudoers will be /etc/sudoers and the per-machine one will
be /etc/sudoers.local. To include /etc/sudoers.local from within
/etc/sudoers we would use the following line in /etc/sudoers:
When sudo reaches this line it will suspend processing of the current
file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching
the end of /etc/sudoers.local, the rest of /etc/sudoers will be
processed. Files that are included may themselves include other files.
A hard limit of 128 nested include files is enforced to prevent include
The file name may include the %h escape, signifying the short form of
the host name. I.e., if the machine's host name is "xerxes", then
will cause sudo to include the file /etc/sudoers.xerxes.
The #includedir directive can be used to create a sudo.d directory that
the system package manager can drop sudoers rules into as part of
package installation. For example, given:
sudo will read each file in /etc/sudoers.d, skipping file names that
end in ~ or contain a . character to avoid causing problems with
package manager or editor temporary/backup files. Files are parsed in
sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed
before /etc/sudoers.d/10_second. Be aware that because the sorting is
lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after
/etc/sudoers.d/10_second. Using a consistent number of leading zeroes
in the file names can be used to avoid such problems.
Note that unlike files included via #include, visudo will not edit the
files in a #includedir directory unless one of them contains a syntax
error. It is still possible to run visudo with the -f flag to edit the
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
Long lines can be continued with a backslash ('\') as the last
character on the line.
Whitespace between elements in a list as well as special syntactic
characters in a User Specification ('=', ':', '(', ')') is optional.
The following characters must be escaped with a backslash ('\') when
used as part of a word (e.g. a user name or host name): '!', '=', ':',
',', '(', ')', '\'.
sudo's behavior can be modified by Default_Entry lines, as explained
earlier. A list of all supported Defaults parameters, grouped by type,
are listed below.
always_set_home If enabled, sudo will set the HOME environment variable
to the home directory of the target user (which is root
unless the -u option is used). This effectively means
that the -H option is always implied. Note that HOME
is already set when the the env_reset option is
enabled, so always_set_home is only effective for
configurations where either env_reset is disabled or
HOME is present in the env_keep list. This flag is off
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
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
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
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.
style globbing when matching path names. However,
since it accesses the file system, glob(3) can take a
long time to complete for some patterns, especially
when the pattern references a network file system that
is mounted on demand (automounted). The fast_glob
option causes sudo to use the fnmatch(3) function,
which does not access the file system to do its
matching. The disadvantage of fast_glob is that it is
unable to match relative path names such as ./ls or
../bin/ls. This has security implications when path
names that include globbing characters are used with
the negation operator, '!', as such rules can be
trivially bypassed. As such, this option should not be
used when sudoers contains rules that contain negated
path names which include globbing characters. This
flag is off by default.
fqdn Set this flag if you want to put fully qualified host
names in the sudoers file. I.e., instead of myhost you
would use myhost.mydomain.edu. You may still use the
short form if you wish (and even mix the two). Beware
that turning on fqdn requires sudo to make DNS lookups
which may make sudo unusable if DNS stops working (for
example if the machine is not plugged into the
network). Also note that you must use the host's
official name as DNS knows it. That is, you may not
use a host alias (CNAME entry) due to performance
issues and the fact that there is no way to get all
aliases from DNS. If your machine's host name (as
returned by the hostname command) is already fully
qualified you shouldn't need to set fqdn. This flag is
on by default.
ignore_dot If set, sudo will ignore '.' or '' (current dir) in the
PATH environment variable; the PATH itself is not
modified. This flag is off by default.
If set via LDAP, parsing of /etc/sudoers will be
skipped. This is intended for Enterprises that wish to
prevent the usage of local sudoers files so that only
LDAP is used. This thwarts the efforts of rogue
operators who would attempt to add roles to
/etc/sudoers. When this option is present,
/etc/sudoers does not even need to exist. Since this
option tells sudo how to behave when no specific LDAP
entries have been matched, this sudoOption is only
meaningful for the cn=defaults section. This flag is
off by default.
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-
may be used to control the format of the session ID.
Note that user input may contain sensitive information
such as passwords (even if they are not echoed to the
screen), which will be stored in the log file
unencrypted. In most cases, logging the command output
via log_output is all that is required.
log_output If set, sudo will run the command in a pseudo tty and
log all output that is sent to the screen, similar to
the script(1) command. If the standard output or
standard error is not connected to the user's tty, due
to I/O redirection or because the command is part of a
pipeline, that output is also captured and stored in
separate log files.
Output is logged to the directory specified by the
iolog_dir option (/var/log/sudo-io by default) using a
unique session ID that is included in the normal sudo
log line, prefixed with TSID=. The iolog_file option
may be used to control the format of the session ID.
Output logs may be viewed with the sudoreplay(8)
utility, which can also be used to list or search the
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
mail_always Send mail to the mailto user every time a users runs
sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo
does not enter the correct password. This flag is on
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
sites may wish to disable this as it could be used to
gather information on the location of executables that
the normal user does not have access to. The
disadvantage is that if the executable is simply not in
the user's PATH, sudo will tell the user that they are
not allowed to run it, which can be confusing. This
flag is on by default.
The password prompt specified by passprompt will
normally only be used if the password prompt provided
by systems such as PAM matches the string "Password:".
If passprompt_override is set, passprompt will always
be used. This flag is off by default.
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
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. This flag is off
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. This
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 if the env_reset option has not been
disabled, entries in the env_keep list will override
the value of set_logname. This flag is on by default.
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
with either the setreuid() or setresuid() function.
This flag is off by default.
targetpw If set, sudo will prompt for the password of the user
specified by the -u option (defaults to root) instead
of the password of the invoking user. In addition, the
timestamp file name will include the target user's
name. Note that this flag precludes the use of a uid
not listed in the passwd database as an argument to the
-u option. This flag is off by default.
tty_tickets If set, users must authenticate on a per-tty basis.
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
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 "rsh somehost sudo ls" since rsh(1) does
not allocate a tty. This flag is off by default.
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
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.
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
specify its own umask which will override the value set
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/local/bin/vi".
iolog_dir The top-level directory to use when constructing the
path name for the input/output log directory. Only
used if 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
The following percent (`%') escape sequences are
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.
expanded to the invoking user's login name
expanded to the name of the invoking user's real
expanded to the login name of the user the command
will be run as (e.g. root)
expanded to the group name of the user the command
will be run as (e.g. wheel)
expanded to the local host name without the domain
expanded to the base name of the command being run
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() function.
mailsub Subject of the mail sent to the mailto user. The escape
%h will expand to the host name of the machine.
Default is *** SECURITY information for %h ***.
noexec_file This option is deprecated and will be removed in a
future release of sudo. The path to the noexec file
should now be set in the /etc/sudo.conf file.
passprompt The default prompt to use when asking for a password;
can be overridden via the -p option or the SUDO_PROMPT
environment variable. 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
%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: .
runas_default The default user to run commands as if the -u option is
not specified on the command line. This defaults to
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
timestampowner The owner of the timestamp directory and the timestamps
stored therein. The default is root.
Strings that can be used in a boolean context:
env_file The env_file options 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.
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.
A string containing a sudoers group plugin with optional
arguments. This can be used to implement support for the
nonunix_group syntax described earlier. The string should
consist of the plugin path, either fully-qualified or
relative to the /usr/libexec 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 example, given /etc/sudo-group, a group file in Unix
group format, the sample group plugin can be used:
Defaults group_plugin="sample_group.so /etc/sudo-group"
For more information see sudo_plugin(5).
lecture This option controls when a short lecture will be printed
along with the password prompt. It has the following
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.
Path to a file containing an alternate sudo lecture that
will be used in place of the standard lecture if the named
any At least one of the user's sudoers entries for the
current host must have the NOPASSWD flag set to
avoid entering a password.
never The user need never enter a password to use the -l
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
all All the user's sudoers entries for the current host
must have the NOPASSWD flag set to avoid entering a
always The user must always enter a password to use the -v
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
o It consists of a fully-qualified path name,
optionally prefixed with a colon (':'), that does
not match the location of the zoneinfo directory.
o It contains a .. path element.
o It contains white space or non-printable
o 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 default 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 default list of
environment variables to remove is
displayed when sudo is run by root
with the -V option. Note that many
operating systems will remove
potentially dangerous variables from
the environment of any setuid process
(such as sudo).
env_keep Environment variables to be preserved
in the user's environment when the
with the -V option.
/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/lib/sudo Directory containing time stamps for the
sudoers security policy
/etc/environment Initial environment for -i mode on Linux and
Below are example sudoers entries. Admittedly, some of these are a bit
contrived. First, we allow a few environment variables to pass and
then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .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 = 126.96.36.199/255.255.0.0
Host_Alias CSNETS = 188.8.131.52, 184.108.40.206/24, 220.127.116.11
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,\
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
Additionally, on the machines in the SERVERS Host_Alias, we keep an
additional local log file and make sure we log the year in each log
line since the log entries will be kept around for several years.
Lastly, we disable shell escapes for the commands in the PAGERS
Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less).
# Override built-in defaults
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
The User specification is the part that actually determines who may run
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as
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 18.104.22.168, 22.214.171.124, and 126.96.36.199). Of
those networks, only 188.8.131.52 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 184.108.40.206).
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
The user pete is allowed to change anyone's password except for root on
the HPPA machines. Note that this assumes passwd(1) does not take
multiple user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user
listed in the OP Runas_Alias (root and operator).
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup.
sudo knows that "biglab" is a netgroup due to the '+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as
well as add and remove users, so they are allowed to run those commands
on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is
not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the
SERVERS Host_Alias (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in
the directory /usr/bin/ except for those commands belonging to the SU
and SHELLS Cmnd_Aliases.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory
/usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS User_Alias (will, wendy,
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
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or
SHELLS since he can simply copy those commands to a different name, or
use a shell escape from an editor or other program. Therefore, these
kind of restrictions should be considered advisory at best (and
reinforced by policy).
Furthermore, if the fast_glob option is in use, it is not possible to
reliably negate commands where the path name includes globbing (aka
wildcard) characters. This is because the C library's fnmatch(3)
function cannot resolve relative paths. While this is typically only
an inconvenience for rules that grant privileges, it can result in a
security issue for rules that subtract or revoke privileges.
For example, given the following sudoers entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run /usr/bin/passwd root if fast_glob is enabled by
changing to /usr/bin and running ./passwd root instead.
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.
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.
sudoers will check the ownership of its time stamp directory
(/var/lib/sudo 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. On
systems that allow non-root users to give away files via chown(2), if
the time stamp directory is located in a world-writable directory
(e.g., /tmp), it is possible for a user to create the time stamp
directory before sudo is run. However, because sudoers checks the
ownership and mode of the directory and its contents, the only damage
that can be done is to "hide" files by putting them in the time stamp
dir. This is unlikely to happen since once the time stamp dir is owned
by root and inaccessible by any other user, the user placing files
there would be unable to get them back out.
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
sudo will log and complain. This is done to keep a user from creating
his/her own time stamp with a bogus date on systems that allow users to
give away files if the time stamp directory is located in a world-
On systems where the boot time is available, sudoers will ignore time
stamps that date from before the machine booted.
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 time stamp file's
modification time is within 15 minutes (or whatever the timeout is set
to in sudoers). When the tty_tickets option is enabled, the time stamp
has per-tty granularity but still may outlive the user's session. On
Linux systems where the devpts filesystem is used, Solaris systems with
the devices filesystem, as well as other systems that utilize a devfs
filesystem that monotonically increase the inode number of devices as
they are created (such as Mac OS X), sudoers is able to determine when
The sudoers file should always be edited by the visudo command which
locks the file and does grammatical checking. It is imperative that
sudoers be free of syntax errors since sudo will not run with a
syntactically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you store
fully qualified host name in the netgroup (as is usually the case), you
either need to have the machine's host name be fully qualified as
returned by the hostname command or use the fqdn option in sudoers.
If you feel you have found a bug in sudo, please submit a bug report at
Limited free support is available via the sudo-users mailing list, see
http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search
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
http://www.sudo.ws/sudo/license.html for complete details.
1.8.3 September 16, 2011 SUDOERS(5)
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