sudoers
— list of
which users may execute what
The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are 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_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
implementation. For instance, the QAS AD backend 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 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.
Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List command name ::= file name | file name args | file name '""' Cmnd ::= '!'* 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 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.
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? Tag_Spec* Cmnd Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')' SELinux_Spec ::= ('ROLE=role' | 'TYPE=type') 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_List
s (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_List
s are specified,
the command may be run with any combination of users and groups listed in
their respective
Runas_List
s. 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 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.
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
Cmnd
s 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.
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.
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
POSIX
glob(3) and fnmatch(3) routines. Note
that these are not regular expressions.
*
?
[...]
[!...]
\x
*
’,
‘?
’,
‘[
’, and
‘]
’.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. 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.local
the 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 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.
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 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.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 hosts 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
xyzzy
If 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=
”.
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=
”.
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 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. 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. 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 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.-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. In addition, the time stamp file name will include the target user's
name. 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 file named for the tty
the user is logged in on in the user's time stamp directory. If disabled,
the time stamp of the directory is used instead. 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 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
default is /var/log/sudo-io.%h
will expand to the host name of the machine.
Default is “*** SECURITY information for %h
***
”.execv
(),
execve
()
and
fexecve
()
library functions that just return an error. This is used to implement the
noexec functionality on systems that support
LD_PRELOAD
or its equivalent. Defaults to
/usr/local/libexec/sudo_noexec.so.-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:
”.
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. The default is /var/adm/sudo.root
.sudo
is built with
SELinux support.Strings that can be used in a boolean context:
sudo
is
executed from a graphical (as opposed to text-based) application. The
program specified by askpass should display the argument
passed to it as the prompt and write the user's password to the standard
output. The value of askpass may be overridden by the
SUDO_ASKPASS
environment variable.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.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.Below 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 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 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
.
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudoers.ldap(5), 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.