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SUDOERS(5) MAINTENANCE COMMANDS SUDOERS(5)
NAME
sudoers - list of which users may execute what
DESCRIPTION
The sudoers file is composed of two types of entries: aliases (basically variables)
and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are
multiple matches, the last match is used (which is not necessarily the most spe-
cific 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 defini-
tions 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 lan-
guage. EBNF also contains the following operators, which many readers will recog-
nize from regular expressions. Do not, however, confuse them with "wildcard" char-
acters, 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 sym-
bol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and
Cmnd_Alias.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* |
'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
'Host_Alias' Host_Alias (':' Host_Alias)* |
'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
User_Alias ::= NAME '=' User_List
Runas_Alias ::= NAME '=' Runas_List
Host_Alias ::= NAME '=' Host_List
Cmnd_Alias ::= NAME '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A
NAME is a string of uppercase letters, numbers, and underscore characters ('_'). A
NAME must start with an uppercase letter. It is possible to put several alias def-
initions 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
Runas_User ::= '!'* username |
'!'* '#'uid |
'!'* '%'group |
'!'* +netgroup |
'!'* Runas_Alias
A Runas_List is similar to a User_List except that it can also contain uids (pre-
fixed 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 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 netmask along with the
network number, sudo will query each of the local host's network interfaces and, if
the network number corresponds to one of the hosts's network interfaces, the corre-
sponding netmask will be used. The netmask may be specified either in standard IP
address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation
(number of bits, e.g. 24 or 64). A 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 wild-
cards 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 wild-
cards 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_List |
'Defaults' ':' User_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are implicitly
boolean and can be turned off via the '!' operator. Some integer, string and list
parameters may also be used in a boolean context to disable them. Values may be
enclosed in double quotes (") when they contain multiple words. Special characters
may be escaped with a backslash (\).
Lists have two additional assignment operators, += and -=. These operators are
used to add to and delete from a list respectively. It is not an error to use the
-= operator to remove an element that does not exist in a list.
See "SUDOERS OPTIONS" for a list of supported Defaults parameters.
User Specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List ')'
Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |
'SETENV:' | 'NOSETENV:')
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:
Runas_Spec
A Runas_Spec is simply a Runas_List (as defined above) enclosed in a set of paren-
theses. 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 six possible
tag values, NOPASSWD, PASSWD, NOEXEC, EXEC, SETENV and NOSETENV. Once a tag is set
on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it is
overridden by the opposite tag (i.e.: PASSWD overrides NOPASSWD and NOEXEC over-
rides EXEC).
NOPASSWD and PASSWD
By default, sudo requires that a user authenticate him or herself before running a
command. This behavior can be modified via the NOPASSWD tag. Like a Runas_Spec,
the NOPASSWD tag sets a default for the commands that follow it in the
Cmnd_Spec_List. Conversely, the PASSWD tag can be used to reverse things. For
example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on
the machine rushmore 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. Addition-
ally, a user may only run sudo -v without a password if the NOPASSWD tag is present
for all a user's entries that pertain to the current host. This behavior may be
overridden via the verifypw and listpw options.
NOEXEC and EXEC
If sudo has been compiled with noexec support and the underlying operating system
supports it, the NOEXEC tag can be used to prevent a dynamically-linked executable
from running further commands itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but
shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the "PREVENTING SHELL ESCAPES" section below for more details on how NOEXEC
works and whether or not it will work on your system.
SETENV and NOSETENV
These tags override the value of the setenv option on a per-command basis. Note
that if SETENV has been set for a command, any environment variables set on the
command line way are not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users should be allowed to set
variables in this manner. If the command matched is ALL, the SETENV tag is implied
for that command; this default may be overridden by use of the UNSETENV tag.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be used in path-
names 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 expres-
sions.
* 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 path-
name. When matching the command line arguments, however, a slash does get matched
by wildcards. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string "" is the only command line argument in the sudoers
entry it means that command is not allowed to be run with any arguments.
Other special characters and reserved words
The pound sign ('#') is used to indicate a comment (unless it is part of a #include
directive or unless it occurs in the context of a user name and is followed by one
or more digits, in which case it is treated as a uid). Both the comment character
and any text after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to succeed.
It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias,
Runas_Alias, or Host_Alias. You should not try to define your own alias called ALL
as the built-in alias will be used in preference to your own. Please note that
using ALL can be dangerous since in a command context, it allows the user to run
any command on the system.
An exclamation point ('!') can be used as a logical not operator both in an alias
and in front of a Cmnd. This allows one to exclude certain values. Note, however,
that using a ! in conjunction with the built-in ALL alias to allow a user to run
"all but a few" commands rarely works as intended (see SECURITY NOTES below).
Long lines can be continued with a backslash ('\') as the last character on the
line.
Whitespace between elements in a list as well as special syntactic characters in a
User Specification ('=', ':', '(', ')') is optional.
The following characters must be escaped with a backslash ('\') when used as part
of a word (e.g. a username or hostname): '@', '!', '=', ':', ',', '(', ')', '\'.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained earlier. A
list of all supported Defaults parameters, grouped by type, are listed below.
Flags:
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.
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.
env_editor If set, visudo will use the value of the EDITOR or VISUAL environ-
ment 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 alter-
native is to place a colon-separated list of editors in the editor
variable. visudo will then only use the EDITOR or VISUAL if they
match a value specified in editor. This flag is on by default.
env_reset If set, sudo will reset the environment to only contain the LOG-
NAME, SHELL, USER, USERNAME and the SUDO_* variables. Any vari-
ables in the caller's environment that match the env_keep and
env_check lists are then added. The default contents of the
env_keep and env_check lists are displayed when sudo is run by root
with the -V option. If sudo was compiled with the SECURE_PATH
option, its value will be used for the PATH environment variable.
This flag is on 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.mydo-
main.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 com-
mand) is already fully qualified you shouldn't need to set fqdn.
This flag is off by default.
ignore_dot If set, sudo will ignore '.' or '' (current dir) in the PATH envi-
ronment variable; the PATH itself is not modified. This flag is on
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).
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be skipped. This is
intended for Enterprises that wish to prevent the usage of local
sudoers files so that only LDAP is used. This thwarts the efforts
of rogue operators who would attempt to add roles to /etc/sudoers.
When this option is present, /etc/sudoers does not even need to
exist. Since this option tells sudo how to behave when no specific
LDAP entries have been matched, this sudoOption is only meaningful
for the cn=defaults section. This flag is off by default.
insults If set, sudo will insult users when they enter an incorrect pass-
word. This flag is off 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.
long_otp_prompt When validating with a One Time Password (OPT) scheme such as S/Key
or OPIE, a two-line prompt is used to make it easier to cut and
paste the challenge to a local window. It's not as pretty as the
default but some people find it more convenient. This flag is off
by default.
mail_always Send mail to the mailto user every time a users runs sudo. This
flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo does not
enter the correct password. This flag is off by default.
mail_no_host If set, mail will be sent to the mailto user if the invoking user
exists in the sudoers file, but is not allowed to run commands on
the current host. This flag is off by default.
mail_no_perms If set, mail will be sent to the mailto user if the invoking user
is allowed to use sudo but the command they are trying is not
listed in their sudoers file entry or is explicitly denied. This
flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if the invoking user
is not in the sudoers file. This flag is on by default.
noexec If set, all commands run via sudo will behave as if the NOEXEC tag
has been set, unless overridden by a EXEC tag. See the description
of NOEXEC and EXEC below as well as the "PREVENTING SHELL ESCAPES"
section at the end of this manual. This flag is off by default.
path_info Normally, sudo will tell the user when a command could not be found
in their PATH environment variable. Some sites may wish to disable
this as it could be used to gather information on the location of
executables that the normal user does not have access to. The dis-
advantage is that if the executable is simply not in the user's
PATH, sudo will tell the user that they are not allowed to run it,
which can be confusing. This flag is on by default.
passprompt_override
The password prompt specified by passprompt will normally only be
used if the passwod prompt provided by systems such as PAM matches
the string "Password:". If passprompt_override is set, passprompt
will always be used. This flag is off by default.
preserve_groups By default sudo will initialize the group vector to the list of
groups the target user is in. When preserve_groups is set, the
user's existing group vector is left unaltered. The real and
effective group IDs, however, are still set to match the target
user. This flag is off by default.
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.
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.
rootpw If set, sudo will prompt for the root password instead of the pass-
word of the invoking user. This flag is off by default.
runaspw If set, sudo will prompt for the password of the user defined by
the runas_default option (defaults to root) instead of the password
of the invoking user. This flag is off by default.
set_home If 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.
set_logname Normally, sudo will set the LOGNAME, USER and USERNAME environment
variables to the name of the target user (usually root unless the
-u 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 desirable to change this behavior. This can
be done by negating the set_logname option. Note that if the
env_reset option has not been disabled, entries in the env_keep
list will override the value of set_logname. This flag is off by
default.
setenv Allow the user to disable the env_reset option from the command
line. Additionally, environment variables set via the command line
are not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users should be
allowed to set variables in this manner. This flag is off by
default.
shell_noargs If set and sudo is invoked with no arguments it acts as if the -s
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.
stay_setuid Normally, when sudo executes a command the real and effective UIDs
are set to the target user (root by default). This option changes
that behavior such that the real UID is left as the invoking user's
UID. In other words, this makes sudo act as a setuid wrapper.
This can be useful on systems that disable some potentially danger-
ous functionality when a program is run setuid. This option is
only effective on systems with either the setreuid() or setresuid()
function. This flag is off by default.
targetpw If set, sudo will prompt for the password of the user specified by
the -u 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.
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
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
on 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 word wrap).
passwd_timeout Number of minutes before the sudo password prompt times out. The
default is 5; set this to 0 for no password timeout.
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 timestamp will
never expire. This can be used to allow users to create or delete
their own timestamps via sudo -v and sudo -k respectively.
umask Umask to use when running the command. Negate this option or set
it to 0777 to preserve the user's umask. The default is 0022.
Strings:
badpass_message Message that is displayed if a user enters an incorrect password.
The default is Sorry, try again. unless insults are enabled.
editor A colon (':') separated list of editors allowed to be used with
visudo. visudo will choose the editor that matches the user's EDI-
TOR 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.
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 ***.
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/libexec/sudo_noexec.so.
passprompt The default prompt to use when asking for a password; can be over-
ridden via the -p option or the SUDO_PROMPT environment variable.
The following percent ('%') escapes are supported:
%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)
%h expanded to the local hostname without the domain name
%p expanded to the user whose password is being asked for
(respects the rootpw, targetpw and runaspw flags in sudoers)
%U expanded to the login name of the user the command will be run
as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into a single %
character
The default value is Password:.
runas_default The default user to run commands as if the -u 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 specifi-
cations.
syslog_badpri Syslog priority to use when user authenticates unsuccessfully.
Defaults to alert.
syslog_goodpri Syslog priority to use when user authenticates successfully.
Defaults to notice.
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.
Strings that can be used in a boolean context:
exempt_group
Users in this group are exempt from password and PATH requirements.
This is not set by default.
lecture This option controls when a short lecture will be printed along with
the password prompt. It has the following possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied. Negating the
option results in a value of never being used. The default value is
once.
lecture_file
Path to a file containing an alternate sudo lecture that will be used
in place of the standard lecture if the named file exists. By default,
sudo uses a built-in lecture.
listpw This option controls when a password will be required when a user runs
sudo with the -l 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.
always The user must always enter a password to use the -l flag.
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.
If no value is specified, a value of any is implied. Negating the
option results in a value of never being used. The default value is
any.
logfile Path to the sudo log file (not the syslog log file). Setting a path
turns on logging to a file; negating this option turns it off. By
default, sudo logs via syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail. Defaults to the path
to sendmail found at configure time.
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.
syslog Syslog facility if syslog is being used for logging (negate to disable
syslog logging). Defaults to authpriv.
verifypw This option controls when a password will be required when a user runs
sudo with the -v 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.
always The user must always enter a password to use the -v flag.
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.
If no value is specified, a value of all is implied. Negating the
option results in a value of never being used. The default value is
all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the user's environment if
the variable's value contains % or / characters. This can be used
to guard against printf-style format vulnerabilities in poorly-
written programs. The argument may be a double-quoted, space-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. Regardless of whether the
env_reset option is enabled or disabled, variables specified by
env_check will be preserved in the environment if they pass the
aforementioned check. The default list of environment variables to
check is displayed when sudo is run by root with the -V option.
env_delete Environment variables to be removed from the user's environment.
The argument may be a double-quoted, space-separated list or a sin-
gle value without double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =, +=, -=, and ! opera-
tors respectively. The default list of environment variables to
remove is displayed when sudo is run by root with the -V option.
Note that many operating systems will remove potentially dangerous
variables from the environment of any setuid process (such as
sudo).
env_keep Environment variables to be preserved in the user's environment
when the env_reset option is in effect. This allows fine-grained
control over the environment sudo-spawned processes will receive.
The argument may be a double-quoted, space-separated list or a sin-
gle value without double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =, +=, -=, and ! opera-
tors respectively. The default list of variables to keep is dis-
played when sudo is run by root with the -V option.
When logging via syslog(3), sudo accepts the following values for the syslog facil-
ity (the value of the syslog Parameter): authpriv (if your OS supports it), auth,
daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
The following syslog priorities are supported: alert, crit, debug, emerg, err,
info, notice, and warning.
FILES
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
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 specifications. The basic rule of thumb is you cannot refer-
ence 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
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to log via
syslog(3) using the auth facility in all cases. We don't want to subject the full
time staff to the sudo lecture, user millert need not give a password, and we don't
want to reset the LOGNAME, USER or USERNAME environment variables when running com-
mands as root. Additionally, on the machines in the SERVERS Host_Alias, we keep an
additional local log file and make sure we log the year in each log line since the
log entries will be kept around for several years. Lastly, we disable shell
escapes for the commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and
/usr/bin/less).
# Override built-in defaults
Defaults syslog=auth
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host
without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (bostley, jwfox, and crawl) may run any command on any host but
they must authenticate themselves first (since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks
128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those networks, only
128.138.204.0 has an explicit netmask (in CIDR notation) indicating it is a class C
network. For the other networks in CSNETS, the local machine's netmask will be
used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the class B net-
work 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 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 operator).
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo knows
that "biglab" is a netgroup due to the '+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add
and remove users, so they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias (oracle or sybase)
without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is not allowed
to 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 direc-
tory /usr/bin/ except for those commands belonging to the SU and SHELLS
Cmnd_Aliases.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/ but
only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung pro-
cesses.
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 '!' opera-
tor. A user can trivially circumvent this by copying the desired command to a dif-
ferent name and then executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or SHELLS since
he can simply copy those commands to a different name, or use a shell escape from
an editor or other program. Therefore, these kind of restrictions should be con-
sidered advisory at best (and reinforced 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 uncom-
mon for a program to allow shell escapes, which lets a user bypass sudo's access
control and logging. Common programs that permit shell escapes include shells
(obviously), editors, paginators, mail and terminal programs.
There are two basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user to run arbi-
trary commands. Many editors have a restricted mode where shell escapes
are disabled, though sudoedit is a better solution to running editors via
sudo. Due to the large number of programs that offer shell escapes,
restricting users to the set of programs that do not if often unworkable.
noexec Many systems that support shared libraries have the ability to override
default library functions by pointing an environment variable (usually
LD_PRELOAD) to an alternate shared library. On such systems, sudo's
noexec functionality can be used to prevent a program run by sudo from
executing any other programs. Note, however, that this applies only to
native dynamically-linked executables. Statically-linked executables and
foreign executables running under binary emulation are not affected.
To tell whether or not sudo supports noexec, you can run the following as
root:
sudo -V | grep "dummy exec"
If the resulting output contains a line that begins with:
File containing dummy exec functions:
then sudo may be able to replace the exec family of functions in the
standard library with its own that simply return an error. 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
system's manual pages for the dynamic linker (usually ld.so, ld.so.1,
dyld, dld.sl, rld, or loader) to see if LD_PRELOAD is supported.
To enable noexec for a command, use the NOEXEC tag as documented in the
User Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec
enabled. This will prevent those two commands from executing other com-
mands (such as a shell). If you are unsure whether or not your system is
capable of supporting noexec you can always just try it out and see if it
works.
Note that restricting shell escapes is not a panacea. Programs running as root are
still capable of many potentially hazardous operations (such as changing or over-
writing 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 syntactically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you store fully quali-
fied 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/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
DISCLAIMER
sudo is provided ''AS IS'' and any express or implied warranties, including, but
not limited to, the implied warranties of merchantability and fitness for a partic-
ular purpose are disclaimed. See the LICENSE file distributed with sudo or
http://www.sudo.ws/sudo/license.html for complete details.
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