SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
sudoers - list of which users may execute what
The sudoers file is composed of two types of entries: aliases (basically variables) and
user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are
multiple matches, the last match is used (which is not necessarily the most specific
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
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
? Means that the preceding symbol (or group of symbols) is optional. That is, it may
appear once or not at all.
* Means that the preceding symbol (or group of symbols) may appear zero or more times.
+ Means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes
('') to designate what is a verbatim character string (as opposed to a symbol name).
There are four kinds of aliases: 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
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* '#'uid |
'!'* '%'group |
'!'* '+'netgroup |
'!'* '%:'nonunix_group |
A User_List is made up of one or more user names, uids (prefixed with '#'), system groups
(prefixed with '%'), netgroups (prefixed with '+') 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, group, netgroup or nonunix_group 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.
The nonunix_group syntax depends on the underlying implementation. For instance, the QAS
AD backend supports the following formats:
o Group in the same domain: "Group Name"
o Group in any domain: "Group Name@FULLY.QUALIFIED.DOMAIN"
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 the '@' symbol.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* '#'uid |
'!'* '%'group |
'!'* +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
commandname ::= file name |
file name args |
file name '""'
Cmnd ::= '!'* commandname |
'!'* directory |
'!'* "sudoedit" |
A Cmnd_List is a list of one or more commandnames, directories, and other aliases. A
commandname is a fully qualified file name which may include shell-style wildcards (see
the Wildcards section below). A simple file name allows the user to run the command with
any arguments he/she wishes. However, you may also specify command line arguments
(including wildcards). Alternately, you can specify "" to indicate that the command may
only be run without command line arguments. A directory is a fully qualified path name
ending in a '/'. When you specify a directory in a Cmnd_List, the user will be able to
run any file within that directory (but not in any subdirectories therein).
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 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 |
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
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_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? 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-
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
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
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
We can extend this to allow dgb to run /bin/ls with either the user or group set to
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \
In the following example, user tcm may run commands that access a modem device file with
the dialer group. Note that in this example only the group will be set, the command still
runs as user tcm.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \
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 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.
NOEXEC and EXEC
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.
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, any environment variables set on the command line way
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:
match /usr/bin/who but not /usr/bin/X11/xterm.
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 entry it
means that command is not allowed to be run with any arguments.
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 will be /etc/sudoers
and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from
within /etc/sudoers we would use the following line in /etc/sudoers:
When sudo reaches this line it will suspend processing of the current file (/etc/sudoers)
and switch to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest
of /etc/sudoers will be processed. Files that are included may themselves include other
files. A hard limit of 128 nested include files is enforced to prevent include file
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
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.
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 both in an alias and in
front of a Cmnd. This allows one to exclude certain values. Note, however, that using a
! in conjunction with the built-in ALL alias to allow a user to run "all but a few"
commands rarely works as intended (see SECURITY NOTES below).
Long lines can be continued with a backslash ('\') as the last character on the line.
Whitespace between elements in a list as well as special syntactic characters in a User
Specification ('=', ':', '(', ')') is optional.
The following characters must be escaped with a backslash ('\') when used as part of a
word (e.g. a user name or host name): '@', '!', '=', ':', ',', '(', ')', '\'.
sudo's behavior can be modified by Default_Entry lines, as explained earlier. A list of
all supported Defaults parameters, grouped by type, are listed below.
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 env_reset is
disabled. 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.
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.
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 reset the environment to only contain the LOGNAME, MAIL,
SHELL, USER, USERNAME and the SUDO_* variables. Any variables in the
caller's environment that match the env_keep and env_check lists are then
added. The default contents of the env_keep and env_check lists are
displayed when sudo is run by root with the -V option. If the secure_path
option is set, its value will be used for the PATH environment variable.
This flag is on by default.
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
(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
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-syslog) sudo log file.
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 (OPT) 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_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 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.
noexec If set, all commands run via sudo will behave as if the NOEXEC tag has
been set, unless overridden by a EXEC tag. See the description of NOEXEC
and EXEC below as well as the "PREVENTING SHELL ESCAPES" section at the
end of this manual. This flag is off by default.
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
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
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 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. 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 the env_reset option is
enabled, so set_home is only effective for configurations where env_reset
is disabled. 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 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.
setenv Allow the user to disable the env_reset option from the command line.
Additionally, environment variables set via the command line are not
subject to the restrictions imposed by env_check, env_delete, or env_keep.
As such, only trusted users should be allowed to set variables in this
manner. This flag is off by default.
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
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
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.
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.
Input is logged to the /var/log/sudo-io directory using a unique session
ID that is included in the normal sudo log line, prefixed with TSID=.
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 /var/log/sudo-io directory using a unique session
ID that is included in the normal sudo log line, prefixed with TSID=.
Output logs may be viewed with the sudoreplay(8) utility, which can also
be used to list or search the available logs.
tty_tickets If set, users must authenticate on a per-tty basis. With this flag
enabled, sudo will use a file named for the tty the user is logged in on
in the user's time stamp directory. If disabled, the time stamp of the
directory is used instead. This flag is on by default.
umask_override If set, sudo will set the umask as specified by sudoers without
modification. This makes it possible to specify a more permissive umask
in sudoers than the user's own umask and matches historical behavior. If
umask_override is not set, sudo will set the umask to be the union of the
user's umask and what is specified in sudoers. This flag is off by
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
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 is 3.
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 value less than 0 the user's
timestamp will never expire. This can be used to allow users to create or
delete their own timestamps via sudo -v and sudo -k respectively.
umask 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
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".
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 Path to a shared library containing dummy versions of the execv(),
execve() and fexecve() library functions that just return an error. This
is used to implement the noexec functionality on systems that support
LD_PRELOAD or its equivalent. Defaults to /usr/lib/sudo/sudo_noexec.so.
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 (`%') escapes are supported:
%H expanded to the local host name including the domain name (on if the
machine's host name is fully qualified or the fqdn option is set)
%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: .
runas_default The default user to run commands as if the -u option is not specified on
the command line. This defaults to root. Note that if runas_default is
set it must occur before any Runas_Alias specifications.
syslog_badpri Syslog priority to use when user authenticates unsuccessfully. Defaults
syslog_goodpri Syslog priority to use when user authenticates successfully. Defaults to
sudoers_locale Locale to use when parsing the sudoers file. Note that changing the
locale may affect how sudoers is interpreted. Defaults to "C".
timestampdir The directory in which sudo stores its timestamp files. The default is
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:
askpass The askpass option specifies the fully qualified path to a helper program used
to read the user's password when no terminal is available. This may be the
case when sudo is executed from a graphical (as opposed to text-based)
application. The program specified by askpass should display the argument
passed to it as the prompt and write the user's password to the standard
output. The value of askpass may be overridden by the SUDO_ASKPASS
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. This is
not set by default.
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.
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
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 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 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
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
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 set to
syslog Syslog facility if syslog is being used for logging (negate to disable syslog
logging). Defaults to authpriv.
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 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 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 if the
variable's value contains % or / characters. This can be used to guard
against printf-style format vulnerabilities in poorly-written programs.
The argument may be a double-quoted, space-separated list or a single
value without double-quotes. The list can be replaced, added to, deleted
from, or disabled by using the =, +=, -=, 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
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
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 default list of
variables to keep is displayed when sudo is run by root with the -V
When logging via syslog(3), sudo accepts the following values for the syslog facility (the
value of the syslog Parameter): authpriv (if your OS supports it), auth, daemon, user,
local0, local1, local2, local3, local4, local5, local6, and local7. The following syslog
priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
/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
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 = 22.214.171.124/255.255.0.0
Host_Alias CSNETS = 126.96.36.199, 188.8.131.52/24, 184.108.40.206
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
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, \
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).
# 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 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
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
220.127.116.11, 18.104.22.168, and 22.214.171.124). Of those networks, only 126.96.36.199
has an explicit netmask (in CIDR notation) indicating it is a class C network. For the
other networks in CSNETS, the local machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the class B network
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here, those are
commands related to backups, killing processes, the printing system, shutting down the
system, and any commands in the directory /usr/oper/bin/.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves with any group in
the ADMINGRP Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on the HPPA machines.
Note that this assumes passwd(1) does not take multiple user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user listed in the OP
Runas_Alias (root and operator).
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo knows that
"biglab" is a netgroup due to the '+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add and
remove users, so they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias (oracle or sybase)
without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is not allowed to
specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the SERVERS Host_Alias
(master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in the directory
/usr/bin/ except for those commands belonging to the SU and SHELLS 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
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS User_Alias (will, wendy, and wim), may run any
command as user www (which owns the web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion,
perseus, hercules) without entering a password. This is a bit tedious for users to type,
so it is a prime candidate for encapsulating in a shell script.
It is generally not effective to "subtract" commands from ALL using the '!' operator. A
user can trivially circumvent this by copying the desired command to a different name and
then executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or SHELLS since he can
simply copy those commands to a different name, or use a shell escape from an editor or
other program. Therefore, these kind of restrictions should be considered advisory at
best (and reinforced by policy).
Furthermore, if the fast_glob option is in use, it is not possible to reliably negate
commands where the path name includes globbing (aka wildcard) characters. This is because
the C library's fnmatch(3) function cannot resolve relative paths. While this is
typically only an inconvenience for rules that grant privileges, it can result in a
security issue for rules that subtract or revoke privileges.
For example, given the following sudoers entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run /usr/bin/passwd root if fast_glob is enabled by changing to
/usr/bin and running ./passwd root instead.
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 tell whether or not sudo supports noexec, you can run the following as root:
sudo -V | grep "dummy exec"
If the resulting output contains a line that begins with:
File containing dummy exec functions:
then sudo may be able to replace the exec family of functions in the standard
library with its own that simply return an error. Unfortunately, there is no
foolproof way to know whether or not noexec will work at compile-time. noexec
should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX
11.x. It is known not to work on AIX and UnixWare. noexec is expected to work
on most operating systems that support the LD_PRELOAD environment variable.
Check your operating system's manual pages for the dynamic linker (usually
ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if LD_PRELOAD is supported.
To enable noexec for a command, use the NOEXEC tag as documented in the User
Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled.
This will prevent those two commands from executing other commands (such as a
shell). If you are unsure whether or not your system is capable of supporting
noexec you can always just try it out and see if it works.
Note that restricting shell escapes is not a panacea. Programs running as root are still
capable of many potentially hazardous operations (such as changing or overwriting files)
that could lead to unintended privilege escalation. In the specific case of an editor, a
safer approach is to give the user permission to run sudoedit.
rsh(1), su(1), fnmatch(3), glob(3), sudo(8), visudo(8)
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
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 the archives.
sudo is provided ``AS IS'' and any express or implied warranties, including, but not
limited to, the implied warranties of merchantability and fitness for a particular purpose
are disclaimed. See the LICENSE file distributed with sudo or
http://www.sudo.ws/sudo/license.html for complete details.
1.7.4 January 12, 2011 SUDOERS(5)