sudoers | Début | Suivant | Sommaire | Préc.page.lue | Accueil |
Section: MAINTENANCE COMMANDS (5)
Updated: Jun 21, 2008
Sommaire
NAME | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
DESCRIPTION | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).
The sudoers grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you don't know what EBNF is; it is fairly simple, and the definitions below are annotated.
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with ``wildcard'' characters, which have different meanings.
Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all.
Means that the preceding symbol (or group of symbols) may appear zero or more times.
Means that the preceding symbol (or group of symbols) may appear one or more times.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).
Aliases | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
There are four kinds of aliases:
User_Alias
,
Runas_Alias
,
Host_Alias
and
Cmnd_Alias
.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* | 'Runas_Alias' Runas_Alias (':' Runas_Alias)* | 'Host_Alias' Host_Alias (':' Host_Alias)* | 'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
User_Alias ::= NAME '=' User_List
Runas_Alias ::= NAME '=' Runas_List
Host_Alias ::= NAME '=' Host_List
Cmnd_Alias ::= NAME '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of
User_Alias
,
Runas_Alias
,
Host_Alias
,
or
Cmnd_Alias
. A
NAME
is a string of uppercase letters, numbers,
and underscore characters ('_'). A
NAME
must start with an
uppercase letter. It is possible to put several alias definitions
of the same type on a single line, joined by a colon (':'). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias member follow.
User_List ::= User | User ',' User_List
User ::= '!'* 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 (prefixed with '#') and instead of
User_Alias
es
it can contain
Runas_Alias
es. 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 corresponding netmask will be used. The netmask
may be specified either in standard IP address notation
(e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::),
or CIDR notation (number of bits, e.g. 24 or 64). A 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.
Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List
commandname ::= filename | filename args | filename '""'
Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias
A
Cmnd_List
is a list of one or more commandnames, directories, and other
aliases. A commandname is a fully qualified filename which may include
shell-style wildcards (see the Wildcards section below). A simple
filename allows the user to run the command with any arguments he/she
wishes. However, you may also specify command line arguments (including
wildcards). Alternately, you can specify "" to indicate that the command
may only be run without command line arguments. A directory is a
fully qualified pathname ending in a '/'. When you specify a directory
in a
Cmnd_List
, the user will be able to run any file within that directory
(but not in any subdirectories therein).
If a
Cmnd
has associated command line arguments, then the arguments
in the
Cmnd
must match exactly those given by the user on the command line
(or match the wildcards if there are any). Note that the following
characters must be escaped with a '\' if they are used in command
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 | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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 | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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.
Runas_Spec | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
A
Runas_Spec
is simply a
Runas_List
(as defined above)
enclosed in a set of parentheses. If you do not specify a
Runas_Spec
in the user specification, a default
Runas_Spec
of root will be used. A
Runas_Spec
sets the default for
commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm --- but only as operator. E.g.,
$ sudo -u operator /bin/ls.
It is also possible to override a
Runas_Spec
later on in an
entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
Tag_Spec | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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
Cmnd
s in the
Cmnd_Spec_List
, inherit the tag unless it is overridden by the
opposite tag (i.e.:
PASSWD
overrides
NOPASSWD
and
NOEXEC
overrides
EXEC
).
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
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.
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.
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 | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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.
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/*
Exceptions to wildcard rules | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
Other special characters and reserved words | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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 | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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:
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.
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.
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.
If set, sudo will reset the environment to only contain the
LOGNAME, SHELL, USER, USERNAME and the
SUDO_*
variables. Any
variables in the caller's environment that match the
env_keep
and
env_check
lists are then added. The default contents of the
env_keep
and
env_check
lists are displayed when sudo is
run by root with the -V option. If sudo was compiled with
the
SECURE_PATH
option, its value will be used for the
PATH
environment variable. This flag is on by default.
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.
If set, sudo will ignore '.' or '' (current dir) in the
PATH
environment 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).
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.
If set, sudo will insult users when they enter an incorrect password. This flag is off by default.
If set, the hostname will be logged in the (non-syslog) sudo log file. This flag is off by default.
If set, the four-digit year will be logged in the (non-syslog) sudo log file. This flag is off by default.
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.
Send mail to the mailto user every time a users runs sudo. This flag is off by default.
Send mail to the mailto user if the user running sudo does not enter the correct password. This flag is off by default.
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.
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.
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.
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.
Normally, sudo will tell the user when a command could not be
found in their
PATH
environment variable. Some sites may wish
to disable this as it could be used to gather information on the
location of executables that the normal user does not have access
to. The disadvantage is that if the executable is simply not in
the user's
PATH
, sudo will tell the user that they are not
allowed to run it, which can be confusing. This flag is on
by default.
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.
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.
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.
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.
If set, sudo will prompt for the root password instead of the password of the invoking user. This flag is off by default.
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.
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.
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.
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.
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.
Normally, when sudo executes a command the real and effective UIDs are set to the target user (root by default). This option changes that behavior such that the real UID is left as the invoking user's UID. In other words, this makes sudo act as a setuid wrapper. This can be useful on systems that disable some potentially dangerous functionality when a program is run setuid. This option is only effective on systems with either the setreuid() or setresuid() function. This flag is off by default.
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.
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:
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:
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).
Number of minutes before the sudo password prompt times out.
The default is
5
; set this to 0 for no password 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 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:
Message that is displayed if a user enters an incorrect password.
The default is
Sorry, try again.
unless insults are enabled.
A colon (':') separated list of editors allowed to be used with visudo. visudo will choose the editor that matches the user's EDITOR environment variable if possible, or the first editor in the list that exists and is executable. The default is the path to vi on your system.
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 ***
.
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.
The default prompt to use when asking for a password; can be overridden
via the -p option or the
SUDO_PROMPT
environment variable.
The following percent (`
%
') escapes are supported:
expanded to the local hostname including the domain name (on if the machine's hostname is fully qualified or the fqdn option is set)
expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
expanded to the login name of the user the command will be run as (defaults to root)
two consecutive
%
characters are collapsed into a single
%
character
The default value is
[sudo] password for %p:
.
The default SELinux role to use when constructing a new security context to run the command. The default role may be overridden on a per-command basis in sudoers or via command line options.
This option is only available whe sudo is built with SELinux support.
The default user to run commands as if the -u flag is not specified
on the command line. This defaults to
root
.
Note that if runas_default is set it must occur before
any
Runas_Alias
specifications.
Syslog priority to use when user authenticates unsuccessfully.
Defaults to
alert
.
Syslog priority to use when user authenticates successfully.
Defaults to
notice
.
The directory in which sudo stores its timestamp files.
The default is /var/run/sudo.
The owner of the timestamp directory and the timestamps stored therein.
The default is
root
.
The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in sudoers or via command line options.
This option is only available whe sudo is built with SELinux support.
Strings that can be used in a boolean context:
Users in this group are exempt from password and PATH requirements.
This is not set by default.
This option controls when a short lecture will be printed along with the password prompt. It has the following possible values:
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.
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.
This option controls when a password will be required when a user runs sudo with the -l flag. It has the following possible values:
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.
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.
Path to mail program used to send warning mail. Defaults to the path to sendmail found at configure time.
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 facility if syslog is being used for logging (negate to
disable syslog logging). Defaults to
authpriv
.
This option controls when a password will be required when a user runs sudo with the -v flag. It has the following possible values:
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:
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-separated list or a single value without double-quotes. The
list can be replaced, added to, deleted from, or disabled by using
the
=
,
+=
,
-=
, and
!
operators respectively. Regardless
of whether the
env_reset
option is enabled or disabled, variables
specified by
env_check
will be preserved in the environment if
they pass the aforementioned check. The default list of environment
variables to check is displayed when sudo is run by root with
the -V option.
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 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).
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. The default list of variables to keep
is displayed when sudo is run by root with the -V option.
When logging via syslog(3), sudo accepts the following values for the syslog facility (the value of the syslog Parameter): authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7. The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
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EXAMPLES | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
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 reference an Alias that has not already been defined.
Below are example sudoers entries. Admittedly, some of these are a bit contrived. First, we define our aliases:
# User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim
# Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase
# Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want
sudo to log via syslog(3) using the auth facility in all
cases. We don't want to subject the full time staff to the sudo
lecture, user millert need not give a password, and we don't
want to reset the
LOGNAME
,
USER
or
USERNAME
environment
variables when running commands as root. Additionally, on the
machines in the SERVERS
Host_Alias
, we keep an additional
local log file and make sure we log the year in each log line since
the log entries will be kept around for several years. Lastly, we
disable shell escapes for the commands in the PAGERS
Cmnd_Alias
(/usr/bin/more, /usr/bin/pg and /usr/bin/less).
# Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL %wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (bostley, jwfox, and crawl) may run any
command on any host but they must authenticate themselves first
(since the entry lacks the
NOPASSWD
tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those networks, only 128.138.204.0 has an explicit netmask (in CIDR notation) indicating it is a class C network. For the other networks in CSNETS, the local machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory /usr/oper/bin/.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-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 directory /usr/bin/ except for those commands
belonging to the SU and SHELLS
Cmnd_Aliases
.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS
User_Alias
(will,
wendy, and wim), may run any command as user www (which owns the
web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias
(orion, perseus, hercules) without entering a password.
This is a bit tedious for users to type, so it is a prime candidate
for encapsulating in a shell script.
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It is generally not effective to ``subtract'' commands from
ALL
using the '!' operator. A user can trivially circumvent this
by copying the desired command to a different name and then
executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or SHELLS since he can simply copy those commands to a different name, or use a shell escape from an editor or other program. Therefore, these kind of restrictions should be considered advisory at best (and reinforced by policy).
PREVENTING SHELL ESCAPES | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
Once sudo executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass sudo's access control and logging. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs.
There are two basic approaches to this problem:
Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though sudoedit is a better solution to running editors via sudo. Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not if often unworkable.
Many systems that support shared libraries have the ability to
override default library functions by pointing an environment
variable (usually
LD_PRELOAD
) to an alternate shared library.
On such systems, sudo's noexec functionality can be used to
prevent a program run by sudo from executing any other programs.
Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreign executables running under binary emulation are not affected.
To tell whether or not sudo supports noexec, you can run the following as root:
sudo -V | grep "dummy exec"
If the resulting output contains a line that begins with:
File containing dummy exec functions:
then sudo may be able to replace the exec family of functions
in the standard library with its own that simply return an error.
Unfortunately, there is no foolproof way to know whether or not
noexec will work at compile-time. noexec should work on
SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX
11.x. It is known not to work on AIX and UnixWare. noexec
is expected to work on most operating systems that support the
LD_PRELOAD
environment variable. Check your operating system's
manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld,
dld.sl, rld, or loader) to see if
LD_PRELOAD
is supported.
To enable noexec for a command, use the
NOEXEC
tag as documented
in the User Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and see if it works.
Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer approach is to give the user permission to run sudoedit.
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CAVEATS | Début | Précédent | Suivant | Sommaire | Préc.page.lue | Accueil |
The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperative that sudoers be free of syntax errors since sudo will not run with a syntactically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you
store fully qualified 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.
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If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/
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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.
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sudo is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with sudo or http://www.sudo.ws/sudo/license.html for complete details.
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