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If a user who is not listed in the policy tries to run a command
via sudo, mail is sent to the proper authorities. The address
used for such mail is configurable via the mailto Defaults entry
(described later) and defaults to
root
.
Note that mail will not be sent if an unauthorized user tries to run sudo with the -l or -v option. This allows users to determine for themselves whether or not they are allowed to use sudo.
If sudo is run by root and the
SUDO_USER
environment variable
is set, the sudoers policy will use this value to determine who
the actual user is. This can be used by a user to log commands
through sudo even when a root shell has been invoked. It also
allows the -e option to remain useful even when invoked via a
sudo-run script or program. Note, however, that the sudoers
lookup is still done for root, not the user specified by
SUDO_USER
.
sudoers uses time stamp files for credential caching. Once a
user has been authenticated, a time stamp is updated and the user
may then use sudo without a password for a short period of time
(
15
minutes unless overridden by the timeout option.
By default, sudoers uses a tty-based time stamp which means that
there is a separate time stamp for each of a user's login sessions.
The tty_tickets option can be disabled to force the use of a
single time stamp for all of a user's sessions.
sudoers can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default, sudoers will log via syslog(3) but this is changeable via the syslog and logfile Defaults settings.
sudoers also supports logging a command's input and output
streams. I/O logging is not on by default but can be enabled using
the log_input and log_output Defaults flags as well as the
LOG_INPUT
and
LOG_OUTPUT
command tags.
By default, the env_reset option is enabled. This causes commands
to be executed with a minimal environment containing
TERM
,
PATH
,
HOME
,
MAIL
,
SHELL
,
LOGNAME
,
USER
and
USERNAME
in
addition to variables from the invoking process permitted by the
env_check and env_keep options. This is effectively a whitelist
for environment variables.
If, however, the env_reset option is disabled, any variables not explicitly denied by the env_check and env_delete options are inherited from the invoking process. In this case, env_check and env_delete behave like a blacklist. Since it is not possible to blacklist all potentially dangerous environment variables, use of the default env_reset behavior is encouraged.
In all cases, environment variables with a value beginning with
()
are removed as they could be interpreted as bash functions.
The list of environment variables that sudo allows or denies is
contained in the output of
sudo -V
when run as root.
Note that the dynamic linker on most operating systems will remove
variables that can control dynamic linking from the environment of
setuid executables, including sudo. Depending on the operating
system this may include
_RLD*
,
DYLD_*
,
LD_*
,
LDR_*
,
LIBPATH
,
SHLIB_PATH
, and others. These type of variables are
removed from the environment before sudo even begins execution
and, as such, it is not possible for sudo to preserve them.
As a special case, if sudo's -i option (initial login) is specified, sudoers will initialize the environment regardless of the value of env_reset. The DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user. On Linux and AIX systems the contents of /etc/environment are also included. All other environment variables are removed.
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.
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).
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 ::= '!'* user name | '!'* #uid | '!'* %group | '!'* %#gid | '!'* +netgroup | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* User_Alias
A
User_List
is made up of one or more user names, user ids
(prefixed with '#'), system group names and ids (prefixed with '%'
and '%#' respectively), netgroups (prefixed with '+'), non-Unix
group names and IDs (prefixed with '%:' and '%:#' respectively) and
User_Alias
es. Each list item may be prefixed with zero or more
'!' operators. An odd number of '!' operators negate the value of
the item; an even number just cancel each other out.
A
user name
,
uid
,
group
,
gid
,
netgroup
,
nonunix_group
or
nonunix_gid
may be enclosed in double quotes to avoid the
need for escaping special characters. Alternately, special characters
may be specified in escaped hex mode, e.g. \x20 for space. When
using double quotes, any prefix characters must be included inside
the quotes.
The actual
nonunix_group
and
nonunix_gid
syntax depends on
the underlying group provider plugin (see the group_plugin
description below). For instance, the QAS AD plugin supports the
following formats:
Note that quotes around group names are optional. Unquoted strings must use a backslash (\) to escape spaces and special characters. See ``Other special characters and reserved words'' for a list of characters that need to be escaped.
Runas_List ::= Runas_Member | Runas_Member ',' Runas_List Runas_Member ::= '!'* user name | '!'* #uid | '!'* %group | '!'* %#gid | '!'* %:nonunix_group | '!'* %:#nonunix_gid | '!'* +netgroup | '!'* Runas_Alias
A
Runas_List
is similar to a
User_List
except that instead
of
User_Alias
es it can contain
Runas_Alias
es. 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 user names 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 ::= '!'* host name | '!'* ip_addr | '!'* network(/netmask)? | '!'* +netgroup | '!'* Host_Alias
A
Host_List
is made up of one or more host names, 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 host name may
include shell-style wildcards (see the Wildcards section below),
but unless the
host name
command on your machine returns the fully
qualified host name, you'll need to use the fqdn option for
wildcards to be useful. Note sudo only inspects actual network
interfaces; this means that IP address 127.0.0.1 (localhost) will
never match. Also, the host name ``localhost'' will only match if
that is the actual host name, which is usually only the case for
non-networked systems.
Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List commandname ::= file name | file name args | file name '""' 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 file name which may include
shell-style wildcards (see the Wildcards section below). A simple
file name 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 path name 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 option (or
as sudoedit). It may take command line arguments just as
a normal command does.
Default_Type ::= 'Defaults' | 'Defaults' '@' Host_List | 'Defaults' ':' User_List | 'Defaults' '!' Cmnd_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.
Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas Defaults and finally command defaults.
See ``SUDOERS OPTIONS'' for a list of supported Defaults parameters.
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? (':' Runas_List)? ')' Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' | 'SETENV:' | 'NOSETENV:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')
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.
The basic structure of a user specification is `who where = (as_whom) what'. Let's break that down into its constituent parts:
A
Runas_Spec
sets the default for the 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.
We can extend this to allow dgb to run
/bin/ls
with either
the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \ /usr/bin/lprm
Note that while the group portion of the
Runas_Spec
permits the
user to run as command with that group, it does not force the user
to do so. If no group is specified on the command line, the command
will run with the group listed in the target user's password database
entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls $ sudo -u operator -g operator /bin/ls $ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu, \ /usr/local/bin/minicom
Note that in this example only the group will be set, the command still runs as user tcm. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a
Runas_Spec
, in
which case the user may select any combination of users and groups
via the -u and -g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally setting the group to operator or system.
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 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.
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, the user
may disable the env_reset option from the command line via the
-E option. Additionally, environment variables set on 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. If the command matched
is ALL, the
SETENV
tag is implied for that command; this
default may be overridden by use of the
NOSETENV
tag.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input option on a per-command basis. For more information, see the description of log_input in the ``SUDOERS OPTIONS'' section below.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output option on a per-command basis. For more information, see the description of log_output in the ``SUDOERS OPTIONS'' section below.
POSIX character classes may also be used if your system's glob(3) and fnmatch(3) functions support them. However, because the ':' character has special meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
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.
This can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers will be /etc/sudoers and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers we would use the following line in /etc/sudoers:
When sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops.
The file name may include the %h escape, signifying the short form of the host name. I.e., if the machine's host name is ``xerxes'', then
#include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The
#includedir
directive can be used to create a sudo.d
directory that the system package manager can drop sudoers rules
into as part of package installation. For example, given:
#includedir /etc/sudoers.d
sudo will read each file in /etc/sudoers.d, skipping file
names that end in
~
or contain a
.
character to avoid causing
problems with package manager or editor temporary/backup files.
Files are parsed in sorted lexical order. That is,
/etc/sudoers.d/01_first will be parsed before
/etc/sudoers.d/10_second. Be aware that because the sorting is
lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded
after /etc/sudoers.d/10_second. Using a consistent number
of leading zeroes in the file names can be used to avoid such
problems.
Note that unlike files included via
#include
, visudo will not
edit the files in a
#includedir
directory unless one of them
contains a syntax error. It is still possible to run visudo
with the
-f
flag to edit the files directly.
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 user name or host name): '!', '=', ':', ',', '(', ')', '\'.
Boolean Flags:
Input is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=. The iolog_file option may be used to control the format of the session ID.
Note that user input may contain sensitive information such as passwords (even if they are not echoed to the screen), which will be stored in the log file unencrypted. In most cases, logging the command output via log_output is all that is required.
Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=. The iolog_file option may be used to control the format of the session ID.
Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.
Integers:
Integers that can be used in a boolean context:
Strings:
The following percent (`
%
') escape sequences are supported:
In addition, any escape sequences supported by the system's strftime() function will be expanded.
To include a literal `
%
' character, the string `
%%
' should
be used.
See the iolog_dir option above for a list of supported percent
(`
%
') escape sequences.
In addition to the escape sequences, path names that end in six or
more
X
s will have the
X
s replaced with a unique combination
of digits and letters, similar to the mktemp() function.
The default value is
[sudo] password for %p:
.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
See syslog_badpri for the list of supported syslog priorities.
Strings that can be used in a boolean context:
For example, given /etc/sudo-group, a group file in Unix group format, the sample group plugin can be used:
Defaults group_plugin="sample_group.so /etc/sudo-group"
For more information see sudo_plugin(5).
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 never.
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.
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
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:
# Run X applications through sudo; HOME is used to find the # .Xauthority file. Note that other programs use HOME to find # configuration files and this may lead to privilege escalation! Defaults env_keep += "DISPLAY HOME" # 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 Runas_Alias ADMINGRP = adm, oper # 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-Za-z]*, !/usr/bin/passwd root %opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves
with any group in the ADMINGRP
Runas_Alias
(the adm and oper
groups).
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 user names 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 specify any options to the su(1) command.
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.
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).
Furthermore, if the fast_glob option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges.
For example, given the following sudoers entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*, /usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run
/usr/bin/passwd root
if fast_glob is
enabled by changing to /usr/bin and running
./passwd root
instead.
There are two basic approaches to this problem:
The noexec feature is known to work on SunOS, Solaris, *BSD,
Linux, IRIX, Tru64 UNIX, MacOS X, HP-UX 11.x and AIX 5.3 and above.
It should be supported 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.
On Solaris 10 and higher, noexec uses Solaris privileges instead
of the
LD_PRELOAD
environment variable.
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 check whether shell escapes work when noexec is enabled.
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.
sudoers will not honor time stamps set far in the future. Time
stamps with a date greater than current_time + 2 *
TIMEOUT
will
be ignored and sudo will log and complain. This is done to keep a
user from creating his/her own time stamp with a bogus date on
systems that allow users to give away files if the time stamp directory
is located in a world-writable directory.
On systems where the boot time is available, sudoers will ignore time stamps that date from before the machine booted.
Since time stamp files live in the file system, they can outlive a
user's login session. As a result, a user may be able to login,
run a command with sudo after authenticating, logout, login
again, and run sudo without authenticating so long as the time
stamp file's modification time is within
15
minutes (or
whatever the timeout is set to in sudoers). When the tty_tickets
option is enabled, the time stamp has per-tty granularity but still
may outlive the user's session. On Linux systems where the devpts
filesystem is used, Solaris systems with the devices filesystem,
as well as other systems that utilize a devfs filesystem that
monotonically increase the inode number of devices as they are
created (such as Mac OS X), sudoers is able to determine when a
tty-based time stamp file is stale and will ignore it. Administrators
should not rely on this feature as it is not universally available.
If users have sudo
ALL
there is nothing to prevent them from
creating their own program that gives them a root shell (or making
their own copy of a shell) regardless of any '!' elements in the
user specification.
When using netgroups of machines (as opposed to users), if you
store fully qualified host name in the netgroup (as is usually the
case), you either need to have the machine's host name be fully qualified
as returned by the
hostname
command or use the fqdn option in
sudoers.