SUDOERS(5) MAINTENANCE COMANDS 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). 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 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: UserAlias, RunasAlias, HostAlias
and CmndAlias.
Alias ::= 'UserAlias' UserAlias (':' UserAlias)*
'RunasAlias' RunasAlias (':' RunasAlias)*
'HostAlias' HostAlias (':' HostAlias)*
'CmndAlias' CmndAlias (':' CmndAlias)*
UserAlias ::= NAME '=' UserList
RunasAlias ::= NAME '=' RunasList
HostAlias ::= NAME '=' HostList
CmndAlias ::= NAME '=' CmndList
NAME ::= [A-Z]([A-Z][0-9])*
Each alias definition is of the form
AliasType NAME = item1, item2, ...
where AliasType is one of UserAlias, RunasAlias, HostAlias, or
CmndAlias. 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.,
AliasType NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias member follow.
UserList ::= User
User ',' UserList
User ::= '!'* username
'!'* '%'group
'!'* ']'netgroup
'!'* UserAlias
A UserList 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.
RunasList ::= RunasUser
RunasUser ',' RunasList
RunasUser ::= '!'* username
'!'* '#'uid
'!'* '%'group
'!'* ]netgroup
'!'* RunasAlias
A RunasList is similar to a UserList except that it can also contain
uids (prefixed with '#') and instead of UserAliases it can contain
RunasAliases. 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).
HostList ::= Host
Host ',' HostList
Host ::= '!'* hostname
'!'* ipaddr
'!'* network(/netmask)?
'!'* ']'netgroup
'!'* HostAlias
A HostList 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 host's 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, you'll
need to use the fqdn option for wildcards to be useful.
CmndList ::= Cmnd
Cmnd ',' CmndList
commandname ::= filename
filename args
filename '""'
Cmnd ::= '!'* commandname
'!'* directory
'!'* "sudoedit"
'!'* CmndAlias
A CmndList 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 CmndList, 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 DefaultEntry 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.
DefaultType ::= 'Defaults'
'Defaults' '@' Host
'Defaults' ':' User
'Defaults' '>' RunasUser
DefaultEntry ::= DefaultType ParameterList
ParameterList ::= Parameter
Parameter ',' ParameterList
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:
longotpprompt
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. It's not as
pretty as the default but some people find it more conve-
nient. This flag is off by default.
ignoredot 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 ignoredot in sudoers, its value is not used.
This option should be considered read-only (it will be
fixed in a future version of sudo).
mailalways Send mail to the mailto user every time a users runs sudo.
This flag is off by default.
mailbadpass
Send mail to the mailto user if the user running sudo does
not enter the correct password. This flag is off by
default.
mailnouser
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.
mailnohost
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.
mailnoperms
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.
ttytickets 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 PASWD and
NOPASWD tags. This flag is on by default.
rootsudo 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 rootsudo will also prevent root
and from running sudoedit. Disabling rootsudo provides no
real additional security; it exists purely for historical
reasons. This flag is on by default.
loghost If set, the hostname will be logged in the (non-syslog)
sudo log file. This flag is off by default.
logyear If set, the four-digit year will be logged in the (non-sys-
log) sudo log file. This flag is off by default.
shellnoargs
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 SHEL 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.
sethome 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.
alwayssethome
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.
pathinfo 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 off by default.
preservegroups
By default sudo will initialize the group vector to the
list of groups the target user is in. When preservegroups
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.
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 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 hostname (as returned by the
hostname command) is already fully qualified you shouldn't
need to set fqdn. 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.
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 wish to set this flag to prevent a
user from entering a visible password. This flag is off by
default.
enveditor 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 runasdefault 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.
setlogname 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 setlogname option.
staysetuid 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 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 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.
envreset If set, sudo will reset the environment to only contain the
following variables: HOME, LOGNAME, PATH, SHEL, 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 setlogname option). If sudo was
compiled with the SECUREPATH option, its value will be
used for the PATH environment variable. Other variables
may be preserved with the envkeep option.
useloginclass
If set, sudo will apply the defaults specified for the tar-
get user's 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 SHEL ESCAPES" section at the end of this man-
ual. This flag is off by default.
ignorelocalsudoers
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:
passwdtries
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).
timestamptimeout
Number of minutes that can elapse before sudo will ask for
a passwd again. 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.
passwdtimeout
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 user's 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 ***.
badpassmessage
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/db/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 SUDOPROMPT environ-
ment variable. The following percent (`%') escapes are
supported:
%u expanded to the invoking user's 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 machine's 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:.
runasdefault
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 runasdefault is set it must occur before any
RunasAlias specifications.
sysloggoodpri
Syslog priority to use when user authenticates success-
fully. Defaults to notice.
syslogbadpri
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 user's 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.
noexecfile 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 LDPRELOAD or its
equivalent. Defaults to .
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.
lecturefile
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 local2.
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.
exemptgroup
Users in this group are exempt from password and PATH
requirements. This is not set 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 user's sudoers entries for the current host
must have the NOPASWD flag set to avoid entering a
password.
any At least one of the user's sudoers entries for the
current host must have the NOPASWD 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 user's sudoers entries for the current host
must have the NOPASWD flag set to avoid entering a
password.
any At least one of the user's sudoers entries for the
current host must have the NOPASWD 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:
envcheck Environment variables to be removed from the user's envi-
ronment if the variable's 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.
envdelete Environment variables to be removed from the user's 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).
envkeep Environment variables to be preserved in the user's envi-
ronment when the envreset 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, local00, 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
UserSpec ::= UserList HostList '=' CmndSpecList \
(':' HostList '=' CmndSpecList)*
CmndSpecList ::= CmndSpec
CmndSpec ',' CmndSpecList
CmndSpec ::= RunasSpec? TagSpec* Cmnd
RunasSpec ::= '(' RunasList ')'
TagSpec ::= ('NOPASWD:' 'PASWD:' '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.
Let's break that down into its constituent parts:
RunasSpec
A RunasSpec is simply a RunasList (as defined above) enclosed in a
set of parentheses. If you do not specify a RunasSpec in the user
specification, a default RunasSpec of root will be used. A RunasSpec
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 RunasSpec 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.
TagSpec
A command may have zero or more tags associated with it. There are
four possible tag values, NOPASWD, PASWD, NOEXEC, EXEC. Once a tag
is set on a Cmnd, subsequent Cmnds in the CmndSpecList, inherit the
tag unless it is overridden by the opposite tag (ie: PASWD overrides
NOPASWD and EXEC overrides NOEXEC).
NOPASWD and PASWD
By default, sudo requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
NOPASWD tag. Like a RunasSpec, the NOPASWD tag sets a default for
the commands that follow it in the CmndSpecList. Conversely, the
PASWD tag can be used to reverse things. For example:
ray rushmore = NOPASWD: /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 = NOPASWD: /bin/kill, PASWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASWD tag has no effect on users who are in
the group specified by the exemptgroup option.
By default, if the NOPASWD 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 NOPASWD tag is present for all a user's 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 SHEL 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 user's 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 AL is a built-in alias that always causes a match to
succeed. It can be used wherever one might otherwise use a CmndAlias,
UserAlias, RunasAlias, or HostAlias. You should not try to define
your own alias called AL as the built-in alias will be used in prefer-
ence to your own. Please note that using AL 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
AL 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
/private/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 HostAlias,
UserAlias, and CmndAlias specifications come first, followed by any
DefaultEntry lines, and finally the RunasAlias 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
UserAlias FULTIMERS = millert, mikef, dowdy
UserAlias PARTIMERS = bostley, jwfox, crawl
UserAlias WEBMASTERS = will, wendy, wim
# Runas alias specification
RunasAlias OP = root, operator
RunasAlias DB = oracle, sybase
# Host alias specification
HostAlias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPA = boa, nag, python
HostAlias CUNETS = 128.138.0.0/255.255.0.0
HostAlias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
HostAlias SERVERS = master, mail, www, ns
HostAlias CDROM = orion, perseus, hercules
# Cmnd alias specification
CmndAlias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore
CmndAlias KIL = /usr/bin/kill
CmndAlias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
CmndAlias SHUTDOWN = /usr/sbin/shutdown
CmndAlias HALT = /usr/sbin/halt
CmndAlias REBOT = /usr/sbin/reboot
CmndAlias SHELS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
/usr/local/bin/tcsh, /usr/bin/rsh, \
/usr/local/bin/zsh
CmndAlias 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 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 or
USER environment variables when running commands as root. Addition-
ally, on the machines in the SERVERS HostAlias, 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 !setlogname
Defaults:FULTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS logyear, logfile=/var/log/sudo.log
The User specification is the part that actually determines who may run
what.
root AL = (AL) AL
%wheel AL = (AL) AL
We let root and any user in group wheel run any command on any host as
any user.
FULTIMERS AL = NOPASWD: AL
Full time sysadmins (millert, mikef, and dowdy) may run any command on
any host without authenticating themselves.
PARTIMERS AL = AL
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 NOPASWD tag).
jack CSNETS = AL
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 = AL
The user lisa may run any command on any host in the CUNETS alias (the
class B network 128.138.0.0).
operator AL = DUMPS, KIL, SHUTDOWN, HALT, REBOT, 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 AL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root
The user pete is allowed to change anyone's password except for root on
the HPA machines. Note that this assumes passwd(1) does not take mul-
tiple usernames on the command line.
bob SPARC = (OP) AL : SGI = (OP) AL
The user bob may run anything on the SPARC and SGI machines as any user
listed in the OP RunasAlias (root and operator).
jim ]biglab = AL
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 AL = 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 AL = (DB) NOPASWD: AL
The user fred can run commands as any user in the DB RunasAlias (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 AL, !SERVERS = AL
The user jen may run any command on any machine except for those in the
SERVERS HostAlias (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELS
For any machine in the SERVERS HostAlias, jill may run any commands in
the directory /usr/bin/ except for those commands belonging to the SU
and SHELS CmndAliases.
steve CSNETS = (operator) /usr/local/opcommands/
The user steve may run any command in the directory /usr/local/opcom-
mands/ but only as user operator.
matt valkyrie = KIL
On his personal workstation, valkyrie, matt needs to be able to kill
hung processes.
WEBMASTERS www = (www) AL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS UserAlias (will, wendy,
and wim), may run any command as user www (which owns the web pages) or
simply su(1) to www.
AL CDROM = NOPASWD: /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
HostAlias (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 AL 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 AL = AL, !SU, !SHELS
Doesn't really prevent bill from running the commands listed in SU or
SHELS 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 SHEL 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 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
LDPRELOAD) 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. 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 LDPRELOAD 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 LDPRELOAD 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 machine's 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/
SUPORT
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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