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 (basi
cally 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 conflicting values, 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). Dont despair if you dont 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 lan
guage. 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, con
fuse 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 let
ter. 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 ::= !* username
!* %group
!* +netgroup
!* User_Alias
A User_List is made up of one or more usernames, system groups (pre
fixed with %), netgroups (prefixed with +) and other aliases. Each
list item may be prefixed with one or more ! operators. An odd num
ber of ! operators negate the value of the item; an even number just
cancel each other out.
Runas_List ::= Runas_User
Runas_User , Runas_List
Runas_User ::= !* username
!* #uid
!* %group
!* +netgroup
!* Runas_Alias
A Runas_List is similar to a User_List except that it can also contain
uids (prefixed with #) and instead of User_Aliases it can contain
Runas_Aliases. Note that usernames and groups are matched as strings.
In other words, two users (groups) with the same uid (gid) are consid
ered to be distinct. If you wish to match all usernames 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 ::= !* hostname
!* ip_addr
!* network(/netmask)?
!* +netgroup
!* Host_Alias
A Host_List is made up of one or more hostnames, 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 with a network number, the netmask of the hosts eth
ernet interface(s) will be used when matching. The netmask may be
specified either in dotted quad notation (e.g. 255.255.255.0) or CIDR
notation (number of bits, e.g. 24). A hostname may include shell-style
wildcards (see the Wildcards section below), but unless the hostname
command on your machine returns the fully qualified hostname, youll
need to use the fqdn option for wildcards to be useful.
Cmnd_List ::= Cmnd
Cmnd , Cmnd_List
commandname ::= filename
filename args
filename ""
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 filename which may
include shell-style wildcards (see the Wildcards section below). A
simple filename 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 pathname 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 argu
ments: ,, :, =, \. The special command "sudoedit" is used to
permit a user to run sudo with the -e flag (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, or
commands being run as a specific user.
Default_Type ::= Defaults
Defaults @ Host
Defaults : User
Defaults > RunasUser
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 con
text 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 oper
ators 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.
Flags:
long_otp_prompt
When validating with a One Time Password scheme (S/Key or
OPIE), a two-line prompt is used to make it easier to cut
and paste the challenge to a local window. Its not as
pretty as the default but some people find it more conve
nient. 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. Currently, while it is possi
ble to set ignore_dot in sudoers, its value is not used.
This option should be considered read-only (it will be
fixed in a future version of sudo).
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_user
If set, mail will be sent to the mailto user if the invok
ing user is not in the sudoers file. This flag is on by
default.
mail_no_host
If set, mail will be sent to the mailto user if the invok
ing 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 invok
ing 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.
tty_tickets If set, users must authenticate on a per-tty basis. Nor
mally, sudo uses a directory in the ticket dir with the
same name as the user running it. With this flag enabled,
sudo will use a file named for the tty the user is logged
in on in that directory. 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 com
mands. This default may be overridden via the PASSWD and
NOPASSWD tags. This flag is on 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
and from running sudoedit. Disabling root_sudo provides no
real additional security; it exists purely for historical
reasons. This flag is on by default.
log_host If set, the hostname 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-sys
log) sudo log file. This flag is off by default.
shell_noargs
If set and sudo is invoked with no arguments it acts as if
the -s flag 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 users /etc/passwd entry if not). This flag
is off by default.
set_home If set and sudo is invoked with the -s flag the HOME envi
ronment 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 flag imply -H. This flag is
off by default.
always_set_home
If set, 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
flag is always implied. 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 users PATH, sudo will
tell the user that they are not allowed to run it, which
can be confusing. 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 users 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.
fqdn Set this flag if you want to put fully qualified hostnames
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 hosts 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 machines hostname (as returned by the
hostname command) is already fully qualified you shouldnt
need to set fqdn. This flag is on by default.
insults If set, sudo will insult users when they enter an incorrect
password. This flag is off by default.
requiretty If set, sudo will only run when the user is logged in to a
real tty. This will disallow things like "rsh somehost
sudo ls" since rsh(1) does not allocate a tty. Because it
is not possible to turn off echo when there is no tty
present, some sites may with to set this flag to prevent a
user from entering a visible password. This flag is off by
default.
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.
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.
targetpw If set, sudo will prompt for the password of the user spec
ified by the -u flag (defaults to root) instead of the
password of the invoking user. Note that this precludes
the use of a uid not listed in the passwd database as an
argument to the -u flag. This flag is off by default.
set_logname Normally, sudo will set the LOGNAME and USER environment
variables to the name of the target user (usually root
unless the -u flag 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 desir
able to change this behavior. This can be done by negating
the set_logname option.
stay_setuid Normally, when sudo executes a command the real and effec
tive 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 users UID. In other words, this
makes sudo act as a setuid wrapper. This can be useful on
systems that disable some potentially dangerous functional
ity when a program is run setuid. Note, however, that this
means that sudo will run with the real uid of the invoking
user which may allow that user to kill sudo before it can
log a failure, depending on how your OS defines the inter
action between signals and setuid processes.
env_reset If set, sudo will reset the environment to only contain the
following variables: HOME, LOGNAME, PATH, SHELL, TERM, and
USER (in addition to the SUDO_* variables). Of these, only
TERM is copied unaltered from the old environment. The
other variables are set to default values (possibly modi
fied by the value of the set_logname option). If sudo was
compiled with the SECURE_PATH option, its value will be
used for the PATH environment variable. Other variables
may be preserved with the env_keep option.
use_loginclass
If set, sudo will apply the defaults specified for the tar
get users login class if one exists. Only available if
sudo is configured with the --with-logincap option. This
flag is off by default.
noexec If set, all commands run via sudo will behave as if the
NOEXEC tag has been set, unless overridden by a EXEC tag.
See the description of NOEXEC and EXEC below as well as the
"PREVENTING SHELL ESCAPES" section at the end of this man
ual. This flag is off by default.
ignore_local_sudoers
If set via LDAP, parsing of @sysconfdir@/sudoers will be
skipped. This is intended for an 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 @sysconfdir@/sudoers. When
this option is present, @sysconfdir@/sudoers does not even
need to exist. Since this options 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.
Integers:
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 dis
able word wrap).
timestamp_timeout
Number of minutes that can elapse before sudo will ask for
a passwd again. The default is 15. Set this to 0 to
always prompt for a password. If set to a value less than
0 the users 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.
passwd_timeout
Number of minutes before the sudo password prompt times
out. The default is 0, set this to 0 for no password time
out.
umask Umask to use when running the command. Negate this option
or set it to 0777 to preserve the users umask. The
default is 0022.
Strings:
mailsub Subject of the mail sent to the mailto user. The escape %h
will expand to the hostname of the machine. Default is ***
SECURITY information for %h ***.
badpass_message
Message that is displayed if a user enters an incorrect
password. The default is Sorry, try again. unless insults
are enabled.
timestampdir
The directory in which sudo stores its timestamp files.
The default is /var/run/sudo.
timestampowner
The owner of the timestamp directory and the timestamps
stored therein. The default is root.
passprompt The default prompt to use when asking for a password; can
be overridden via the -p option or the SUDO_PROMPT environ
ment variable. The following percent (%) escapes are
supported:
%u expanded to the invoking users login name
%U expanded to the login name of the user the command
will be run as (defaults to root)
%h expanded to the local hostname without the domain
name
%H expanded to the local hostname including the domain
name (on if the machines hostname is fully quali
fied or the fqdn option is set)
%% two consecutive % characters are collaped into a
single % character
The default value is Password:.
runas_default
The default user to run commands as if the -u flag 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_goodpri
Syslog priority to use when user authenticates success
fully. Defaults to notice.
syslog_badpri
Syslog priority to use when user authenticates unsuccess
fully. Defaults to alert.
editor A colon (:) separated list of editors allowed to be used
with visudo. visudo will choose the editor that matches
the users USER environment variable if possible, or the
first editor in the list that exists and is executable.
The default is the path to vi on your system.
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.
Strings that can be used in a boolean context:
lecture This option controls when a short lecture will be printed
along with the password prompt. It has the following pos
sible values:
never Never lecture the user.
once Only lecture the user the first time they run sudo.
always Always lecture the user.
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.
logfile Path to the sudo log file (not the syslog log file). Set
ting a path turns on logging to a file; negating this
option turns it off.
syslog Syslog facility if syslog is being used for logging (negate
to disable syslog logging). Defaults to authpriv.
mailerpath Path to mail program used to send warning mail. Defaults
to the path to sendmail found at configure time.
mailerflags Flags to use when invoking mailer. Defaults to -t.
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.
exempt_group
Users in this group are exempt from password and PATH
requirements. On Debian systems, this is set to the group
sudo by default.
verifypw This option controls when a password will be required when
a user runs sudo with the -v flag. It has the following
possible values:
all All the users sudoers entries for the current host
must have the NOPASSWD flag set to avoid entering a
password.
any At least one of the users 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
flag.
always The user must always enter a password to use the -v
flag.
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.
listpw This option controls when a password will be required when
a user runs sudo with the -l flag. It has the following
possible values:
all All the users sudoers entries for the current host
must have the NOPASSWD flag set to avoid entering a
password.
any At least one of the users 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
flag.
always The user must always enter a password to use the -l
flag.
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.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the users envi
ronment if the variables value contains % or / characters.
This can be used to guard against printf-style format vul
nerabilities 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. The default list of environment
variables to check is printed when sudo is run by root with
the -V option.
env_delete Environment variables to be removed from the users envi
ronment. The argument may be a double-quoted, space-sepa
rated 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 printed
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 users envi
ronment 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 with
out double-quotes. The list can be replaced, added to,
deleted from, or disabled by using the =, +=, -=, and !
operators respectively. This list has no default members.
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 warn
ing.
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 )
Tag_Spec ::= (NOPASSWD: PASSWD: NOEXEC: EXEC:)
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.
Lets break that down into its constituent parts:
Runas_Spec
A Runas_Spec is simply a Runas_List (as defined above) enclosed in a
set of parentheses. If you do not specify a Runas_Spec in the user
specification, a default Runas_Spec of root will be used. A Runas_Spec
sets the default for 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.
Tag_Spec
A command may have zero or more tags associated with it. There are
four possible tag values, NOPASSWD, PASSWD, NOEXEC, EXEC. 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 (ie: PASSWD overrides
NOPASSWD and EXEC overrides NOEXEC).
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 as root 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 pass
word if the NOPASSWD tag is present for all a users entries that per
tain to the current host. This behavior may be overridden via the ver
ifypw and listpw options.
NOEXEC and EXEC
If sudo has been compiled with noexec support and the underlying oper
ating system support it, the NOEXEC tag can be used to prevent a dynam
ically-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.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be
used in pathnames as well as command line arguments in the sudoers
file. Wildcard matching is done via the POSIX fnmatch(3) routine.
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 "}".
Note that a forward slash (/) will not be matched by wildcards used
in the pathname. 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.
WARNING: a pathname with wildcards will not match a user command that
consists of a relative path. In other words, given the following sudo
ers entry:
billy workstation = /usr/bin/*
user billy will be able to run any command in /usr/bin as root, such as
/usr/bin/w. The following two command will be allowed (the first
assumes that /usr/bin is in the users path):
$ sudo w
$ sudo /usr/bin/w
However, this will not:
$ cd /usr/bin
$ sudo ./w
For this reason you should only grant access to commands using wild
cards and never restrict access using them. This limitation will be
removed in a future version of sudo.
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.
Other special characters and reserved words
The pound sign (#) is used to indicate a comment (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 prefer
ence 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 charac
ter 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 username or hostname): @, !, =,
:, ,, (, ), \.
FILES
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
EXAMPLES
Since the sudoers file is parsed in a single pass, order is important.
In general, you should structure sudoers such that the Host_Alias,
User_Alias, and Cmnd_Alias specifications come first, followed by any
Default_Entry lines, and finally the Runas_Alias and user specifica
tions. The basic rule of thumb is you cannot reference an Alias that
has not already been defined.
Below are example sudoers entries. Admittedly, some of these are a bit
contrived. First, we define our aliases:
# 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
# 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
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 dont
want to subject the full time staff to the sudo lecture, user millert
need not give a password, and we dont want to reset the LOGNAME or
USER environment variables when running commands as root. Addition
ally, 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.
# 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
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 machines 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-z]*, !/usr/bin/passwd root
The user pete is allowed to change anyones password except for root on
the HPPA machines. Note that this assumes passwd(1) does not take mul
tiple usernames 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 (ora
cle 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 give su(1) any flags.
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_com
mands/ 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 exam
ple:
bill ALL = ALL, !SU, !SHELLS
Doesnt 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 rein
forced by policy).
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 sudos restrictions. Common programs that permit
shell escapes include shells (obviously), editors, paginators, mail and
terminal programs.
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, sudos
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. Unfortu
nately, 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 systems manual pages for the dynamic linker (usually ld.so,
ld.so.1, dyld, dld.sl, rld, or loader) to see if LD_PRELOAD is sup
ported.
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 sys
tem is capable of supporting noexec you can always just try it out and
see if it works.
Note that disabling 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), 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 syntac
tically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you store
fully qualified hostnames in the netgroup (as is usually the case), you
either need to have the machines hostname 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
Commercial support is available for sudo, see
http://www.sudo.ws/sudo/support.html for details.
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 merchantabil
ity 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.
1.6.8p12 June 20, 2005 SUDOERS(5)
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