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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
NAME
sudoers - list of which users may execute what
DESCRIPTION
The sudoers file is composed of two types of entries: aliases (basically variables) and user
specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are multiple matches,
the last match is used (which is not necessarily the most specific match).
The sudoers 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.
* Means that the preceding symbol (or group of symbols) may appear zero or more times.
+ Means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to
designate what is a verbatim character string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* |
'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
'Host_Alias' Host_Alias (':' Host_Alias)* |
'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
User_Alias ::= NAME '=' User_List
Runas_Alias ::= NAME '=' Runas_List
Host_Alias ::= NAME '=' Host_List
Cmnd_Alias ::= NAME '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of
uppercase letters, numbers, and underscore characters ('_'). A NAME must start with an uppercase
letter. It is possible to put several alias definitions of the same type on a single line, joined by
a colon (':'). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* '#'uid |
'!'* '%'group |
'!'* '+'netgroup |
'!'* '%:'nonunix_group |
'!'* User_Alias
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:
• Group in the same domain: "Group Name"
• Group in any domain: "Group Name@FULLY.QUALIFIED.DOMAIN"
• Group SID: "S-1-2-34-5678901234-5678901234-5678901234-567"
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 |
'!'* Runas_Alias
A Runas_List is similar to a User_List except that instead of User_Aliases it can contain
Runas_Aliases. Note that user names and groups are matched as strings. In other words, two users
(groups) with the same uid (gid) are considered to be distinct. If you wish to match all user names
with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given).
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* '+'netgroup |
'!'* Host_Alias
A Host_List is made up of one or more host names, IP addresses, network numbers, netgroups (prefixed
with '+') and other aliases. Again, the value of an item may be negated with the '!' operator. 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" |
'!'* Cmnd_Alias
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.
Defaults
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 |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are implicitly boolean and can be
turned off via the '!' operator. Some integer, string and list parameters may also be used in a
boolean context to disable them. Values may be enclosed in double quotes (") when they contain
multiple words. Special characters may be escaped with a backslash (\).
Lists have two additional assignment operators, += and -=. These operators are used to add to and
delete from a list respectively. It is not an error to use the -= operator to remove an element that
does not exist in a list.
Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas
Defaults and finally command defaults.
See "SUDOERS OPTIONS" for a list of supported Defaults parameters.
User Specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? 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:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be run as. A fully-specified
Runas_Spec consists of two Runas_Lists (as defined above) separated by a colon (':') and enclosed in
a set of parentheses. The first Runas_List indicates which users the command may be run as via
sudo's -u option. The second defines a list of groups that can be specified via sudo's -g option.
If both Runas_Lists are specified, the command may be run with any combination of users and groups
listed in their respective Runas_Lists. If only the first is specified, the command may be run as
any user in the list but no -g option may be specified. If the first Runas_List is empty but the
second is specified, the command may be run as the invoking user with the group set to any listed in
the Runas_List. If no Runas_Spec is specified the command may be run as root and no group may be
specified.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the
entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm -- but only as operator. E.g.,
$ sudo -u operator /bin/ls.
It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \
/usr/bin/lprm
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, \
/usr/local/bin/minicom
Tag_Spec
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.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be used in host names, path names
and command line arguments in the sudoers file. Wildcard matching is done via the 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:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
Note that a forward slash ('/') will not be matched by wildcards used in the path name. When
matching the command line arguments, however, a slash does get matched by wildcards. This is to make
a path like:
/usr/bin/*
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:
#include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch
to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be
processed. Files that are included may themselves include other files. A hard limit of 128 nested
include files is enforced to prevent include file loops.
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
#include /etc/sudoers.%h
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:
#includedir /etc/sudoers.d
sudo will read each file in /etc/sudoers.d, skipping file names that end in ~ or contain a .
character to avoid causing problems with package manager or editor temporary/backup files. Files are
parsed in sorted lexical order. That is, /etc/sudoers.d/_1_first will be parsed before
/etc/sudoers.d/1__second. Be aware that because the sorting is lexical, not numeric,
/etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/1__second. Using a consistent number of
leading zeroes in the file names can be used to avoid such problems.
Note that unlike files included via #include, visudo will not edit the files in a #includedir
directory unless one of them contains a syntax error. It is still possible to run visudo with the -f
flag to edit the files directly.
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): '@', '!', '=', ':', ',', '(', ')', '\'.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained earlier. A list of all
supported Defaults parameters, grouped by type, are listed below.
Boolean Flags:
always_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.
closefrom_override
If set, the user may use sudo's -C option which overrides the default starting point
at which sudo begins closing open file descriptors. This flag is off by default.
compress_io If set, and sudo is configured to log a command's input or output, the I/O logs will
be compressed using zlib. This flag is on by default when sudo is compiled with zlib
support.
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 off 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 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 off 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.
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be skipped. This is intended for
Enterprises that wish to prevent the usage of local sudoers files so that only LDAP
is used. This thwarts the efforts of rogue operators who would attempt to add roles
to /etc/sudoers. When this option is present, /etc/sudoers does not even need to
exist. Since this option tells sudo how to behave when no specific LDAP entries have
been matched, this sudoOption is only meaningful for the cn=defaults section. This
flag is off by default.
insults If set, sudo will insult users when they enter an incorrect password. This flag is
off by default.
log_host If set, the host name will be logged in the (non-syslog) sudo log file. This flag is
off by default.
log_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 twoline
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 off by default.
mail_no_host If set, mail will be sent to the mailto user if the invoking user exists in the
sudoers file, but is not allowed to run commands on the current host. This flag is
off by default.
mail_no_perms If set, mail will be sent to the mailto user if the invoking user is allowed to use
sudo but the command they are trying is not listed in their sudoers file entry or is
explicitly denied. This flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if the invoking user is not in the
sudoers file. This flag is on by default.
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 by default.
passprompt_override
The password prompt specified by passprompt will normally only be used if the
password prompt provided by systems such as PAM matches the string "Password:". If
passprompt_override is set, passprompt will always be used. This flag is off by
default.
preserve_groups By default, sudo will initialize the group vector to the list of groups the target
user is in. When preserve_groups is set, the user's existing group vector is left
unaltered. The real and effective group IDs, however, are still set to match the
target user. This flag is off by default.
pwfeedback By default, sudo reads the password like most other Unix programs, by turning off
echo until the user hits the return (or enter) key. Some users become confused by
this as it appears to them that sudo has hung at this point. When pwfeedback is set,
sudo will provide visual feedback when the user presses a key. Note that this does
have a security impact as an onlooker may be able to determine the length of the
password being entered. This flag is off by default.
requiretty If set, sudo will only run when the user is logged in to a real tty. When this flag
is set, sudo can only be run from a login session and not via other means such as
cron(8) or cgi-bin scripts. This flag is off by default.
root_sudo If set, root is allowed to run sudo too. Disabling this prevents users from
"chaining" sudo commands to get a root shell by doing something like "sudo sudo
/bin/sh". Note, however, that turning off root_sudo will also prevent root from
running sudoedit. Disabling root_sudo provides no real additional security; it
exists purely for historical reasons. This flag is on by default.
rootpw If set, sudo will prompt for the root password instead of the password of the
invoking user. 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 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.
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 default.
use_pty If set, sudo will run the command in a pseudo-pty even if no I/O logging is being
gone. A malicious program run under sudo could conceivably fork a background process
that retains to the user's terminal device after the main program has finished
executing. Use of this option will make that impossible.
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.
Integers:
closefrom Before it executes a command, sudo will close all open file descriptors other than
standard input, standard output and standard error (ie: file descriptors 0-2). The
closefrom option can be used to specify a different file descriptor at which to start
closing. The default is 3.
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 5.
timestamp_timeout
Number of minutes that can elapse before sudo will ask for a passwd again. The
timeout may include a fractional component if minute granularity is insufficient, for
example 2.5. The default is 5. 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 0022. This guarantees that sudo never lowers the umask when running
a command. Note on systems that use PAM, the default PAM configuration may specify
its own umask which will override the value set in sudoers.
Strings:
badpass_message Message that is displayed if a user enters an incorrect password. The default is
Sorry, try again. unless insults are enabled.
editor A colon (':') separated list of editors allowed to be used with visudo. visudo will
choose the editor that matches the user's EDITOR environment variable if possible, or
the first editor in the list that exists and is executable. The default is
"/usr/bin/vi".
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/local/libexec/sudo_noexec.dylib.
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 Password:.
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 to alert.
syslog_goodpri Syslog priority to use when user authenticates successfully. Defaults to notice.
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 /var/db/sudo.
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 environment variable.
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.
exempt_group
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 once.
lecture_file
Path to a file containing an alternate sudo lecture that will be used in place of the
standard lecture if the named file exists. By default, sudo uses a built-in lecture.
listpw This option controls when a password will be required when a user runs sudo with the -l
option. It has the following possible values:
all All the user's sudoers 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 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.
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, doublequoted,
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 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 spaceseparated
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 option.
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.
FILES
/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
EXAMPLES
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 = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
/usr/local/bin/tcsh, /usr/bin/rsh, \
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to log via syslog(3) using the
auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user
millert need not give a password, and we don't want to reset the LOGNAME, USER or USERNAME
environment variables when running commands as root. Additionally, on the machines in the SERVERS
Host_Alias, we keep an additional local log file and make sure we log the year in each log line since
the log entries will be kept around for several years. Lastly, we disable shell escapes for the
commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less).
# Override built-in defaults
Defaults syslog=auth
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without
authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (bostley, jwfox, and crawl) may run any command on any host but they must
authenticate themselves first (since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks 128.138.243.0,
128.138.204.0, and 128.138.242.0). Of those networks, only 128.138.204.0 has an explicit netmask (in
CIDR notation) indicating it is a class C network. For the other networks in CSNETS, the local
machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here, those are commands related
to backups, killing processes, the printing system, shutting down the system, and any commands in the
directory /usr/oper/bin/.
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 user
operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS User_Alias (will, wendy, and wim), may run any command as
user www (which owns the web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus,
hercules) without entering a password. This is a bit tedious for users to type, so it is a prime
candidate for encapsulating in a shell script.
SECURITY NOTES
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 if 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.
SEE ALSO
rsh(1), su(1), fnmatch(3), glob(3), sudo(8), visudo(8)
CAVEATS
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.
BUGS
If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/
SUPPORT
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.
DISCLAIMER
sudo is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the
LICENSE file distributed with sudo or http://www.sudo.ws/sudo/license.html for complete details.
1.7.4 July 21, 2010 SUDOERS(5)
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