SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
sudoers - list of which users may execute what
The sudoers file is composed of two types of entries:
aliases (basically variables) and user specifications (which
specify who may run what).
When multiple entries match for a user, they are applied in
order. Where there are 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 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 sym-
bols) is optional. That is, it may appear once or
not at all.
* Means that the preceding symbol (or group of sym-
bols) may appear zero or more times.
+ Means that the preceding symbol (or group of sym-
bols) 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.
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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 ::= '!'* username |
'!'* '%'group |
'!'* '+'netgroup |
'!'* User_Alias
A User_List is made up of one or more usernames, system
groups (prefixed with '%'), netgroups (prefixed with '+')
and other aliases. Each list item may be prefixed with one
or more '!' operators. An odd number of '!' operators negate
the value of the item; an even number just cancel each other
out.
Runas_List ::= Runas_User |
Runas_User ',' Runas_List
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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 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 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 net-
mask with a network number, the netmask of the host's ether-
net 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 Wild-
cards 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.
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, direc-
tories, and other aliases. A commandname is a fully quali-
fied filename which may include shell-style wildcards (see
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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 arguments:
',', ':', '=', '\'. 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 context to disable them. Values
may be enclosed in double quotes (") when they contain mul-
tiple words. Special characters may be escaped with a
backslash (\).
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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.
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. It's not as pretty as the
default but some people find it more convenient.
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 possible 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 invoking 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 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.
tty_tickets If set, users must authenticate on a per-tty
basis. Normally, sudo uses a directory in the
ticket dir with the same name as the user
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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 commands. 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. Disa-
bling 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 pro-
vides 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-syslog) 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
user's /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 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 flag imply -H. This flag is off by
default.
always_set_home
If set, sudo will set the HOME environment vari-
able 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.
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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 confus-
ing. 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.
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 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.
insults If set, sudo will insult users when they enter
an incorrect password. This flag is on 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 pos-
sible 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
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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 specified 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 deter-
mine the real identity of the user, it may be
desirable 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 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 use-
ful on systems that disable some potentially
dangerous functionality 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 interaction 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
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SUDO_* variables). Of these, only TERM is copied
unaltered from the old environment. The other
variables are set to default values (possibly
modified 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 target 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 overrid-
den 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.
ignore_local_sudoers
If set via LDAP, parsing of @sysconfdir@/sudoers
will be skipped. This is intended for an Enter-
prises 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 disable
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word wrap).
timestamp_timeout
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 times-
tamp will never expire. This can be used to
allow users to create or delete their own times-
tamps via sudo -v and sudo -k respectively.
passwd_timeout
Number of minutes before the sudo password
prompt times out. The default is 5, set this to
0 for no password timeout.
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 ***.
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 environment variable. The fol-
lowing 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)
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%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 qualified or the fqdn
option is set)
%% two consecutive % characters are col-
laped 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 specif-
ications.
syslog_goodpri
Syslog priority to use when user authenticates
successfully. Defaults to notice.
syslog_badpri
Syslog priority to use when user authenticates
unsuccessfully. 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.
noexec_file Path to a shared library containing dummy ver-
sions of the execv(), execve() and fexecve()
library functions that just return an error.
This is used to implement the noexec functional-
ity on systems that support LD_PRELOAD or its
equivalent. Defaults to
/usr/libexec/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 possible values:
never Never lecture the user.
once Only lecture the user the first time
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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 lec-
ture 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). Setting a path turns on logging to a
file; negating this option turns it off.
syslog Syslog facility if syslog is being used for log-
ging (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 con-
figure 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. 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 NOPASSWD flag
set to avoid entering a password.
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 flag.
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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 NOPASSWD flag
set to avoid entering a password.
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 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
user's environment if the variable's value con-
tains % or / characters. This can be used to
guard against printf-style format vulnerabili-
ties 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 dis-
abled 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
user's environment. 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 respec-
tively. The default list of environment
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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
user's environment when the env_reset option is
in effect. This allows fine-grained control
over the environment sudo-spawned processes will
receive. The argument may be a double-quoted,
space-separated list or a single value without
double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =,
+=, -=, and ! operators respectively. 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
warning.
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, com-
mands are run as root, but this can be changed on a per-
command basis.
Let's 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
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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 overrid-
den 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 password if the NOPASSWD
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
tag is present for all a user's entries that pertain 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 under-
lying operating system support 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.
Wildcards
sudo allows shell-style wildcards (aka meta or glob charac-
ters) to be used in pathnames as well as command line argu-
ments in the sudoers file. Wildcard matching is done via
the POSIX fnmatch(3) routine. Note that these are not regu-
lar 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 wild-
cards 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 sudoers entry:
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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 wildcards 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 oth-
erwise 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).
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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 username or host-
name): '@', '!', '=', ':', ',', '(', ')', '\'.
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
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 specifica-
tions come first, followed by any Default_Entry lines, and
finally the Runas_Alias and user specifications. 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
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
# 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 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 vari-
ables 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.
# 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).
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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 mainte-
nance. 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 anyone's password except
for root on the HPPA machines. Note that this assumes
passwd(1) does not take multiple 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 opera-
tor).
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.
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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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 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 com-
mands 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.
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:
1.6.8p9 June 20, 2005 21
SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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).
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 res-
trictions. 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, 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 func-
tions 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 environ-
ment 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 docu-
mented in the User Specification section above. Here is
that example again:
1.6.8p9 June 20, 2005 22
SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
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 disabling shell escapes is not a panacea. Pro-
grams running as root are still capable of many potentially
hazardous operations (such as changing or overwriting files)
that could lead to unintended privilege escalation. In the
specific case of an editor, a safer approach is to give the
user permission to run sudoedit.
rsh(1), su(1), fnmatch(3), sudo(8), visudo(8)
The sudoers file should always be edited by the visudo com-
mand 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 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 com-
mand or use the fqdn option in sudoers.
If you feel you have found a bug in sudo, please submit a
bug report at http://www.sudo.ws/sudo/bugs/
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.
Sudo is provided ``AS IS'' and any express or implied war-
ranties, including, but not limited to, the implied warran-
ties 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.
1.6.8p9 June 20, 2005 23