sudoers — default
sudo security policy plugin
The sudoers policy plugin determines a user's
sudo privileges. It is the default
sudo policy plugin. The policy is driven by the
/etc/sudoers file or, optionally in LDAP. The policy
format is described in detail in the
SUDOERS FILE FORMAT section.
For information on storing sudoers policy information in
LDAP, please see sudoers.ldap(5).
sudo consults the
sudo.conf(5) file to determine which policy and and I/O
logging plugins to load. If no sudo.conf(5) file is
present, or if it contains no Plugin lines,
sudoers will be used for policy decisions and I/O
logging. To explicitly configure sudo.conf(5) to use the
sudoers plugin, the following configuration can be
used.
Plugin sudoers_policy sudoers.so Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible
to specify optional arguments to the sudoers plugin
in the sudo.conf(5) file. These arguments, if present,
should be listed after the path to the plugin (i.e. after
sudoers.so). Multiple arguments may be specified,
separated by white space. For example:
Plugin sudoers_policy sudoers.so sudoers_mode=0400
The following plugin arguments are supported:
For more information on configuring sudo.conf(5), please refer to its manual.
The sudoers security policy requires that most
users authenticate themselves before they can use
sudo. A password is not required if the invoking
user is root, if the target user is the same as the invoking user, or if the
policy has disabled authentication for the user or command. Unlike
su(1), when sudoers requires
authentication, it validates the invoking user's credentials, not the target
user's (or root's) credentials. This can be changed via the
rootpw, targetpw and
runaspw flags, described later.
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 per-user time stamp
files for credential caching. Once a user has been authenticated, a record
is written containing the uid that was used to authenticate, the terminal
session ID, and a time stamp (using a monotonic clock if one is available).
The user may then use sudo without a password for a
short period of time (5 minutes unless overridden by
the timeout
option). By default, sudoers uses a separate record for
each tty, which means that a user's login sessions are authenticated
separately. 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.
Since environment variables can influence program behavior, sudoers provides a means to restrict which variables from the user's environment are inherited by the command to be run. There are two distinct ways sudoers can deal with environment variables.
By default, the env_reset option is enabled.
This causes commands to be executed with a new, minimal environment. On AIX
(and Linux systems without PAM), the environment is initialized with the
contents of the /etc/environment file. On BSD
systems, if the use_loginclass option is enabled, the
environment is initialized based on the path and
setenv settings in
/etc/login.conf. The new environment contains the
TERM, PATH,
HOME, MAIL,
SHELL, LOGNAME,
USER, USERNAME and
SUDO_* variables 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 AIX (and Linux systems without PAM), the
contents of /etc/environment are also included. On
BSD systems, if the use_loginclass option is enabled, the
path and setenv variables in
/etc/login.conf are also applied. All other
environment variables are removed.
Finally, if the env_file option is defined, any variables present in that file will be set to their specified values as long as they would not conflict with an existing environment variable.
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 are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of production rules. E.g.,
symbol ::= definition |
alternate1 | alternate2
...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with “wildcard” characters, which have different meanings.
?*+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).
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 ::= '!'* 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_Aliases. 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. For instance, the QAS AD plugin supports the following
formats:
See GROUP PROVIDER PLUGINS for more information.
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_Aliases it can contain
Runas_Aliases. Note that user names and groups are
matched as strings. In other words, two users (groups) with the same uid
(gid) are considered to be distinct. If you wish to match all 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 that
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.
digest ::= [A-Fa-f0-9]+ |
[[A-Za-z0-9+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Cmnd ::= Digest_Spec? '!'* command name |
'!'* directory |
'!'* "sudoedit" |
'!'* Cmnd_Alias
A Cmnd_List is a list of one
or more command names, directories, and other aliases. A command name 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 sub-directories 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 built-in 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. Note that
“sudoedit” is a command built into
sudo itself and must be specified in
sudoers without a leading path.
If a command name is prefixed with a
Digest_Spec, the command will only match
successfully if it can be verified using the specified SHA-2 digest. This
may be useful in situations where the user invoking
sudo has write access to the command or its parent
directory. The following digest formats are supported: sha224, sha256,
sha384 and sha512. The string may be specified in either hex or base64
format (base64 is more compact). There are several utilities capable of
generating SHA-2 digests in hex format such as openssl, shasum, sha224sum,
sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64 EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Command digests are only supported by version 1.8.7 or higher.
Certain configuration options may be changed from their default
values at run-time via one or more Default_Entry
lines. These may affect all users on any host, all users on a specific host,
a specific user, a specific command, or commands being run as a specific
user. Note that per-command entries may not include command line arguments.
If you need to specify arguments, define a
Cmnd_Alias and reference that instead.
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? SELinux_Spec? Solaris_Priv_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Solaris_Priv_Spec ::= ('PRIVS=privset' | 'LIMITPRIVS=privset')
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 determines the user and/or
the group that a command may be run as. A fully-specified
Runas_Spec consists of two
Runas_Lists (as defined above) separated by a colon
(‘:’) and enclosed in a set of
parentheses. The first Runas_List indicates which
users the command may be run as via sudo's
-u option. The second defines a list of groups that
can be specified via sudo's
-g option. If both
Runas_Lists are specified, the command may be run
with any combination of users and groups listed in their respective
Runas_Lists. If only the first is specified, the
command may be run as any user in the list but no -g
option may be specified. If the first Runas_List is
empty but the second is specified, the command may be run as the invoking
user with the group set to any listed in the
Runas_List. If both
Runas_Lists are empty, the command may only be run
as the invoking user. If no Runas_Spec is specified
the command may be run as root and no group may be
specified.
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.
On systems with SELinux support, sudoers entries may optionally have an SELinux role and/or type associated with a command. If a role or type is specified with the command it will override any default values specified in sudoers. A role or type specified on the command line, however, will supersede the values in sudoers.
On Solaris systems, sudoers entries may optionally specify Solaris privilege set and/or limit privilege set associated with a command. If privileges or limit privileges are specified with the command it will override any default values specified in sudoers.
A privilege set is a comma-separated list of privilege names. The ppriv(1) command can be used to list all privileges known to the system. For example:
$ ppriv -l
In addition, there are several “special” privilege strings:
Privileges can be excluded from a set by prefixing the privilege
name with either an ‘!’ or
‘-’ character.
A command may have zero or more tags associated with it. There are
ten possible tag values: NOPASSWD,
PASSWD, NOEXEC,
EXEC, SETENV,
NOSETENV, LOG_INPUT,
NOLOG_INPUT, LOG_OUTPUT and
NOLOG_OUTPUT. 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 (in other words,
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 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, 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.
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.
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.
sudo allows shell-style
wildcards
(aka meta or glob characters) to be used in host names, path names and
command line arguments in the sudoers file. Wildcard
matching is done via the glob(3) and
fnmatch(3) functions as specified by IEEE
Std 1003.1 (“POSIX.1”). Note that these are
not regular expressions.
*?[...][!...]\x*’,
‘?’,
‘[’, and
‘]’.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. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care.
Because command line arguments are matched as a single, concatenated string,
a wildcard such as ‘?’ or
‘*’ can match multiple words. For
example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended.
The following exceptions apply to the above rules:
"""" is the only
command line argument in the sudoers entry it means that
command is not allowed to be run with any
arguments./’) will not be matched by a
wildcard.It is possible to include other sudoers files
from within the sudoers file currently being parsed using
the #include and #includedir
directives.
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:
#include /etc/sudoers.local
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.
If the path to the include file is not fully-qualified (does not
begin with a ‘/’, it must be located
in the same directory as the sudoers file it was included from. For example,
if /etc/sudoers contains the line:
#include sudoers.localthe file that will be included is /etc/sudoers.local.
The file name may also include the %h
escape, signifying the short form of the host name. In other words, 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 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 in a list or
alias as well as in front of a
Cmnd. This allows one to exclude certain values. For
the ‘!’ operator to be effective,
there must be something for it to exclude. For example, to match all users
except for root one would use:
ALL,!root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is different from a true “negation” operator.
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.
White space 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): ‘!’,
‘=’,
‘:’,
‘,’,
‘(’,
‘)’,
‘\’.
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.
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 option is always implied. Note that
HOME is already set when the
env_reset option is enabled, so
always_set_home
is only effective for configurations where either
env_reset is disabled or HOME is
present in the env_keep list. This flag is
off by default.PASSWD and
NOPASSWD tags. This flag is on
by default.sudo's
-C option which overrides the default starting
point at which sudo begins closing open file
descriptors. This flag is off by default.sudo is configured to log a command's
input or output, the I/O logs will be compressed using
zlib. This flag is on by default when
sudo is compiled with zlib
support.+’), may be used in place of a user
or host. For LDAP-based sudoers, netgroup support requires an expensive
substring match on the server. If netgroups are not needed, this option
can be disabled to reduce the load on the LDAP server. This flag is
on by default.sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When the
exec_background
flag is enabled and the command is being run in a pty (due to I/O logging
or the use_pty flag), the command will be run as a
background process. Attempts to read from the controlling terminal (or to
change terminal settings) will result in the command being suspended with
the SIGTTIN signal (or
SIGTTOU in the case of terminal settings). If this
happens when sudo is a foreground process, the
command will be granted the controlling terminal and resumed in the
foreground with no user intervention required. The advantage of initially
running the command in the background is that sudo
need not read from the terminal unless the command explicitly requests it.
Otherwise, any terminal input must be passed to the command, whether it
has required it or not (the kernel buffers terminals so it is not possible
to tell whether the command really wants the input). This is different
from historic sudo behavior or when the command is not
being run in a pty.
For this to work seamlessly, the operating
system must support the automatic restarting of system calls.
Unfortunately, not all operating systems do this by default, and even
those that do may have bugs. For example, Mac OS X fails to restart the
tcgetattr()
and
tcsetattr()
system calls (this is a bug in Mac OS X). Furthermore, because this
behavior depends on the command stopping with the
SIGTTIN or SIGTTOU
signals, programs that catch these signals and suspend themselves with a
different signal (usually SIGTOP) will not be
automatically foregrounded. Some versions of the linux
su(1) command behave this way.
This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O logging is enabled or the use_pty flag is enabled.
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
off by default.sudo will run the command in a minimal
environment containing the TERM,
PATH, HOME,
MAIL, SHELL,
LOGNAME, USER,
USERNAME and SUDO_*
variables. Any variables in the caller's environment that match the
env_keep and env_check
lists are then added, followed by any variables present in the file
specified by the env_file option (if any). The default
contents of the env_keep and
env_check lists are displayed when
sudo is run by root with the
-V option. If the secure_path
option is set, its value will be used for the PATH
environment variable. This flag is on by default.sudo uses the glob(3)
function to do shell-style globbing when matching path names. However,
since it accesses the file system, glob(3) can take a
long time to complete for some patterns, especially when the pattern
references a network file system that is mounted on demand (auto mounted).
The fast_glob option causes sudo
to use the fnmatch(3) function, which does not access
the file system to do its matching. The disadvantage of
fast_glob is that it is unable to match relative path
names such as ./ls or
../bin/ls. This has security implications when
path names that include globbing characters are used with the negation
operator, ‘!’, as such rules can be
trivially bypassed. As such, this option should not be used when
sudoers contains rules that contain negated path names
which include globbing characters. This flag is off by
default.hostname command) does not contain the domain
name. In other words, instead of myhost you would use myhost.mydomain.edu.
You may still use the short form if you wish (and even mix the two). This
option is only effective when the “canonical” host name, as
returned by the
getaddrinfo()
or
gethostbyname()
function, is a fully-qualified domain name. This is usually the case when
the system is configured to use DNS for host name resolution.
If the system is configured to use the
/etc/hosts file in preference to DNS, the
“canonical” host name may not be fully-qualified. The
order that sources are queried for host name resolution is usually
specified in the /etc/nsswitch.conf,
/etc/netsvc.conf,
/etc/host.conf, or, in some cases,
/etc/resolv.conf file. In the
/etc/hosts file, the first host name of the
entry is considered to be the “canonical” name; subsequent
names are aliases that are not used by sudoers.
For example, the following hosts file line for the machine
“xyzzy” has the fully-qualified domain name as the
“canonical” host name, and the short version as an
alias.
192.168.1.1 xyzzy.sudo.ws
xyzzyIf the machine's hosts file entry is not formatted properly, the fqdn option will not be effective if it is queried before DNS.
Beware that when using DNS for host name resolution, turning
on fqdn requires sudoers to
make DNS lookups which renders sudo unusable if
DNS stops working (for example if the machine is disconnected from the
network). Also note that just like with the hosts file, you must use the
“canonical” 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.
This flag is off by default.
sudo will ignore "." or
"" (both denoting current directory) in the
PATH environment variable; the
PATH itself is not modified. This flag is
off by default.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.sudo will insult users when they enter an
incorrect password. This flag is off by default.sudo log file. This flag is off
by default.sudo will run the command in a
pseudo tty and log all user input. If the standard input
is not connected to the user's tty, due to I/O redirection or because the
command is part of a pipeline, that input is also captured and stored in a
separate log file.
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.
sudo will run the command in a
pseudo tty and log all output that is sent to the
screen, similar to the script(1) command. If the
standard output or standard error is not connected to the user's tty, due
to I/O redirection or because the command is part of a pipeline, that
output is also captured and stored in separate log files.
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.
sudo log file. This flag is off
by default.sudo. This flag is off by
default.sudo does not enter the correct password. If the
command the user is attempting to run is not permitted by
sudoers and one of the
mail_always,
mail_no_host,
mail_no_perms
or
mail_no_user
flags are set, this flag will have no effect. This flag is
off by default.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.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.sudo
will create a new PAM session for the command to be run in. Disabling
pam_session may be needed on older PAM implementations
or on operating systems where opening a PAM session changes the utmp or
wtmp files. If PAM session support is disabled, resource limits may not be
updated for the command being run. If pam_session,
pam_setcred, and use_pty are disabled
and I/O logging has not been configured, sudo will
execute the command directly instead of running it as a child process.
This flag is on by default.
This setting is only supported by version 1.8.7 or higher.
sudo
will attempt to establish credentials for the target user by default, if
supported by the underlying authentication system. One example of a
credential is a Kerberos ticket. If pam_session,
pam_setcred, and use_pty are disabled
and I/O logging has not been configured, sudo will
execute the command directly instead of running it as a child process.
This flag is on by default.
This setting is only supported by version 1.8.8 or higher.
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.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.sudo reads the password like most
other Unix programs, by turning off echo until the user hits the return
(or enter) key. Some users become confused by this as it appears to them
that sudo has hung at this point. When
pwfeedback
is set, sudo will provide visual feedback when the
user presses a key. Note that this does have a security impact as an
onlooker may be able to determine the length of the password being
entered. This flag is off by default.sudo will only run when the user is logged
in to a real tty. When this flag is set, sudo can
only be run from a login session and not via other means such as
cron(8) or cgi-bin scripts. This flag is
off by default.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 from running sudoedit. Disabling
root_sudo provides no real additional security; it
exists purely for historical reasons. This flag is on by
default.sudo will prompt for the root password
instead of the password of the invoking user when running a command or
editing a file. This flag is off by default.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 when running a command or editing a file. This flag
is off by default.sudo is invoked with the
-s option 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 option imply
-H. Note that HOME is
already set when the env_reset option is enabled, so
set_home is
only effective for configurations where either env_reset
is disabled or HOME is present in the
env_keep list. This flag is off by
default.sudo will set the
LOGNAME, USER and
USERNAME environment variables to the name of the
target user (usually root unless the -u option 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 on by default.sudo will create an entry in the
utmp (or utmpx) file when a pseudo-tty is allocated. A pseudo-tty is
allocated by sudo when the
log_input, log_output or
use_pty flags are enabled. By default, the new entry
will be a copy of the user's existing utmp entry (if any), with the tty,
time, type and pid fields updated. This flag is on by
default.-E option. 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.sudo is invoked with no arguments it
acts as if the -s option 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.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 that
support either the setreuid(2) or
setresuid(2) system call. This flag is
off by default.sudo will prompt for the password of the
user specified by the -u option (defaults to
root) instead of the password of the invoking user
when running a command or editing a file. Note that this flag precludes
the use of a uid not listed in the passwd database as an argument to the
-u option. This flag is off by
default.sudo will use a separate record in the
time stamp file for each tty. If disabled, a single record is used for all
login sessions. This flag is on by default.sudo will set the umask as specified by
sudoers without modification. This makes it possible to
specify a more permissive umask in sudoers than the
user's own umask and matches historical behavior. If
umask_override
is not set, sudo will set the umask to be the
union of the user's umask and what is specified in
sudoers. This flag is off by
default.sudo will apply the defaults specified for
the target user's login class if one exists. Only available if
sudo is configured with the
--with-logincap option. This flag is
off by default.sudo will run the command in a pseudo-pty
even if no I/O logging is being gone. A malicious program run under
sudo could conceivably fork a background process
that retains to the user's terminal device after the main program has
finished executing. Use of this option will make that impossible. This
flag is off by default.sudo will store the name of the runas user
when updating the utmp (or utmpx) file. By default,
sudo stores the name of the invoking user. This
flag is off by default.sudo will refuse to run if the user
must enter a password but it is not possible to disable echo on the
terminal. If the
visiblepw
flag is set, sudo will prompt for a password even
when it would be visible on the screen. This makes it possible to run
things like “ssh somehost sudo ls”
since by default, ssh(1) does not allocate a tty when
running a command. This flag is off by default.Integers:
sudo will close all
open file descriptors other than standard input, standard output and
standard error (ie: file descriptors 0-2). The
closefrom
option can be used to specify a different file descriptor at which to
start closing. The default is 3.sudo logs the failure and exits. The default is
3.Integers that can be used in a boolean context:
80 (use 0 or negate the option to disable word
wrap).sudo password prompt
times out, or 0 for no timeout. The timeout may
include a fractional component if minute granularity is insufficient, for
example 2.5. The default is
5.sudo will
ask for a passwd again. The timeout may include a fractional component if
minute granularity is insufficient, for example
2.5. 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 time stamp will
never expire. This can be used to allow users to create or delete their
own time stamps via “sudo -v” and
“sudo -k” respectively.0022. This guarantees that
sudo never lowers the umask when running a
command. Note: on systems that use PAM, the default PAM configuration may
specify its own umask which will override the value set in
sudoers.Strings:
Sorry, try again. unless insults are
enabled.:’) 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
vi.LOG_INPUT or LOG_OUTPUT
tags are present for a command. The session sequence number, if any, is
stored in the directory. The default is
/var/log/sudo-io.
The following percent
(‘%’) escape sequences are
supported:
%{seq}%{user}%{group}%{runas_user}%{runas_group}%{hostname}%{command}In addition, any escape sequences supported by the system's strftime(3) function will be expanded.
To include a literal ‘%’
character, the string ‘%%’ should
be used.
LOG_INPUT or LOG_OUTPUT
tags are present for a command. Note that iolog_file may
contain directory components. The default is
“%{seq}”.
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 Xs will have the
Xs replaced with a unique combination of digits
and letters, similar to the mktemp(3) function.
If the path created by concatenating
iolog_dir and iolog_file already
exists, the existing I/O log file will be truncated and overwritten
unless iolog_file ends in six or more
Xs.
sudo stores per-user
lecture status files. Once a user has received the lecture, a zero-length
file is created in this directory so that sudo
will not lecture the user again. This directory should
not be cleared when the system reboots. The default is
/var/adm/sudo/lectured.sudoers is built on Solaris 10 or higher.%h will expand to the host name of the machine.
Default is “*** SECURITY information for %h
***”.%{seq}” escape in the I/O log file
(see the iolog_dir description above for more
information). While the value substituted for
“%{seq}” is in base 36,
maxseq itself should be expressed in decimal. Values
larger than 2176782336 (which corresponds to the base 36 sequence number
“ZZZZZZ”) will be silently truncated to 2176782336. The
default value is 2176782336.
Once the local sequence number reaches the value of
maxseq, it will “roll over” to zero,
after which sudoers will truncate and re-use any
existing I/O log path names.
This setting is only supported by version 1.8.7 or higher.
sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should now be set in the
sudo.conf(5) file.-i option is specified. The default value
is “sudo”. See the description of
pam_service
for more information.
This setting is only supported by version 1.8.8 or higher.
sudo”.
This setting is only supported by version 1.8.8 or higher.
-p option or the
SUDO_PROMPT environment variable. The following
percent (‘%’) escape sequences are
supported:
%H%h%p%U%u%%% characters are collapsed
into a single % characterThe default value is
“Password:”.
sudoers is built on Solaris 10 or
higher.sudo is built with
SELinux support.-u
option is not specified on the command line. This defaults to
root.alert.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
notice.
See syslog_badpri for the list of supported syslog priorities.
C”.sudo stores its time stamp
files. This directory should be cleared when the system reboots. The
default is /var/run/sudo/ts.root.sudo is built with
SELinux support.Strings that can be used in a boolean context:
VARIABLE=value” or
“export VARIABLE=value”. The value
may optionally be surrounded by single or double quotes. Variables in this
file are subject to other sudo environment
settings such as env_keep and
env_check.%
prefix. This is not set by default.For more information see GROUP PROVIDER PLUGINS.
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.
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.sudo with the -l option.
It has the following possible values:
NOPASSWD flag set to avoid
entering a password.-l option.NOPASSWD flag set
to avoid entering a password.-l option.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.
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.-t.sudo
interpreting the @ sign. Defaults to the name of
the user running sudo.sudo interpreting the @
sign. Defaults to root.sudo. If you
don't trust the people running sudo to have a sane
PATH environment variable you may want to use
this. Another use is if you want to have the “root path” be
separate from the “user path”. Users in the group specified
by the exempt_group option are not affected by
secure_path. This option is not set by default.auth.
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
sudo with the -v option.
It has the following possible values:
NOPASSWD flag set to avoid
entering a password.-v option.NOPASSWD flag set
to avoid entering a password.-v option.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:
%’ 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.=,
+=, -=, 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).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.The sudoers plugin supports its own plugin
interface to allow non-Unix group lookups which can query a group source
other than the standard Unix group database. This can be used to implement
support for the nonunix_group syntax described
earlier.
Group provider plugins are specified via the group_plugin Defaults setting. The argument to group_plugin should consist of the plugin path, either fully-qualified or relative to the /usr/local/libexec/sudo directory, followed by any configuration options the plugin requires. These options (if specified) will be passed to the plugin's initialization function. If options are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
Defaults group_plugin="group_file.so /etc/sudo-group"
getgrnam()
and
getgrid().
This plugin can be used in instances where the user belongs to groups not
present in the user's supplemental group vector. This plugin takes no
options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(8).
sudoers can log events using either
syslog(3) or a simple log file. In each case the log
format is almost identical.
Commands that sudo runs are logged using the following format (split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
sudo was run on. This field
is only present when logging via syslog(3).sudo.sudo was run on, or “unknown” if
there was no terminal present.sudo was run
in.Messages are logged using the locale specified
by
sudoers_locale,
which defaults to the “C” locale.
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:
sudo's -n option was
specified but a password was required.If an error occurs, sudoers will log a
message and, in most cases, send a message to the administrator via email.
Possible errors include:
sudoers encountered an error when parsing the
specified file. In some cases, the actual error may be one line above or
below the line number listed, depending on the type of error.sudo from running,
but the sudoers file should be checked using
visudo.sudoers tries to open sudoers
using group permissions to avoid this problem. Consider either changing
the ownership of /etc/sudoers or adding an
argument like “sudoers_uid=N” (where ‘N’ is
the user ID that owns the sudoers file) to the end of
the sudoers Plugin line in
the sudo.conf(5) file.sudoers Plugin line in the
sudo.conf(5) file.sudoers
Plugin line in the sudo.conf(5)
file.sudoers Plugin line in the
sudo.conf(5) file.By default, sudoers logs messages via syslog(3). The date, hostname, and progname fields are added by the syslog daemon, not sudoers itself. As such, they may vary in format on different systems.
On most systems, syslog(3) has a relatively
small log buffer. To prevent the command line arguments from being
truncated, sudoers will split up log messages that
are larger than 960 characters (not including the date, hostname, and the
string “sudo”). When a message is split, additional parts will
include the string “(command continued)” after the user name
and before the continued command line arguments.
If the logfile option is set, sudoers will log to a local file, such as /var/log/sudo. When logging to a file, sudoers uses a format similar to syslog(3), with a few important differences:
!’), word wrap will be
disabled.-i mode on AIX and Linux
systemsBelow are example sudoers entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases:
# 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,\ sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \ /home/operator/bin/start_backups 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). Note that this will not
effectively constrain users with sudo
ALL privileges.
# 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/. Note that one
command in the DUMPS Cmnd_Alias includes a sha224
digest, /home/operator/bin/start_backups. This is
because the directory containing the script is writable by the operator
user. If the script is modified (resulting in a digest mismatch) it will no
longer be possible to run it via sudo.
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. While not specifically mentioned in
the rule, the commands in the
PAGERS
Cmnd_Alias all reside in
/usr/bin and have the noexec
option set.
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 nosuidnodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the
CDROM Host_Alias (orion, perseus, hercules) without
entering a password. This is a bit tedious for users to type, so it is a
prime candidate for encapsulating in a shell script.
It is generally not effective to “subtract” commands
from ALL using the
‘!’ operator. A user can trivially
circumvent this by copying the desired command to a different name and then
executing that. For example:
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).
In general, if a user has 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.
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.
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:
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 is often unworkable.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.
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 (see
below).
The sudoers plugin includes
sudoedit support which allows users to securely edit
files with the editor of their choice. As sudoedit
is a built-in command, it must be specified in sudoers
without a leading path. However, it may take command line arguments just as
a normal command does. For example, to allow user operator to edit the
“message of the day” file:
operator sudoedit /etc/motd
The operator user then runs sudoedit as
follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of /etc/motd. After the file has been edited, /etc/motd will be updated with the contents of the temporary copy.
sudoers will check the ownership of its time
stamp directory (/var/run/sudo/ts by default) and
ignore the directory's contents if it is not owned by root or if it is
writable by a user other than root. Older versions of
sudo stored time stamp files in
/tmp; this is no longer recommended as it may be
possible for a user to create the time stamp themselves on systems that
allow unprivileged users to change the ownership of files they create.
While the time stamp directory should be cleared at reboot time, not all systems contain a /var/run directory. To avoid potential problems, sudoers will ignore time stamp files that date from before the machine booted on systems where the boot time is available.
Some systems with graphical desktop
environments allow unprivileged users to change the system clock. Since
sudoers relies on the system clock for time stamp
validation, it may be possible on such systems for a user to run
sudo for longer than
timestamp_timeout
by setting the clock back. To combat this, sudoers uses a
monotonic clock (which never moves backwards) for its time stamps if the
system supports it.
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
sudoers will log and complain.
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 record's time stamp is within 5 minutes
(or whatever value the timeout is set to in sudoers). When
the tty_tickets option is enabled, the time stamp record
includes the device number of the terminal the user authenticated with. This
provides per-tty granularity but time stamp records still may outlive the
user's session. The time stamp record also includes the session ID of the
process that last authenticated. This prevents processes in different
terminal sessions from using the same time stamp record. It also helps
reduce the chance that a user will be able to run
sudo without entering a password when logging out
and back in again on the same terminal.
Versions 1.8.4 and higher of the sudoers
plugin support a flexible debugging framework that can help track down what
the plugin is doing internally if there is a problem. This can be configured
in the sudo.conf(5) file.
The sudoers plugin uses the
same debug flag format as the sudo front-end:
subsystem@priority.
The priorities used by sudoers,
in order of decreasing severity, are: crit,
err,
warn,
notice,
diag,
info,
trace
and debug. Each priority, when specified, also includes
all priorities higher than it. For example, a priority of
notice would include debug messages logged at
notice and higher.
The following subsystems are used by the
sudoers plugin:
User_Alias,
Runas_Alias, Host_Alias
and Cmnd_Alias processingDebug sudo /var/log/sudo_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudoers.ldap(5), sudo_plugin(8), sudo(8), visudo(8)
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 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.
If you feel you have found a bug in sudo,
please submit a bug report at https://www.sudo.ws/sudo/bugs/
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
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 https://www.sudo.ws/sudo/license.html for
complete details.