Copyright (c) 1994-1996, 1998-2005, 2007-2012
Todd C. Miller <Todd.Miller@courtesan.com>
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Sponsored in part by the Defense Advanced Research Projects
Agency (DARPA) and Air Force Research Laboratory, Air Force
Materiel Command, USAF, under agreement number F39502-99-1-0512.
=pod
=head1 NAME
sudoers - default sudo security policy module
=head1 DESCRIPTION
The I<sudoers> policy module determines a user's B<sudo> privileges.
It is the default B<sudo> policy plugin. The policy is driven by
the F<@sysconfdir@/sudoers> file or, optionally in LDAP. The policy
format is described in detail in the L<"SUDOERS FILE FORMAT">
section. For information on storing I<sudoers> policy information
in LDAP, please see L<sudoers.ldap(5)>.
=head2 Authentication and Logging
The I<sudoers> security policy requires that most users authenticate
themselves before they can use B<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 L<su(1)>, when I<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 I<rootpw>, I<targetpw> and I<runaspw> flags, described later.
If a user who is not listed in the policy tries to run a command
via B<sudo>, mail is sent to the proper authorities. The address
used for such mail is configurable via the I<mailto> Defaults entry
(described later) and defaults to C<@mailto@>.
Note that mail will not be sent if an unauthorized user tries to
run B<sudo> with the B<-l> or B<-v> option. This allows users to
determine for themselves whether or not they are allowed to use
B<sudo>.
If B<sudo> is run by root and the C<SUDO_USER> environment variable
is set, the I<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 B<-e> option to remain useful even when invoked via a
sudo-run script or program. Note, however, that the I<sudoers>
lookup is still done for root, not the user specified by C<SUDO_USER>.
I<sudoers> uses time stamp files for credential caching. Once a
user has been authenticated, a time stamp is updated and the user
may then use sudo without a password for a short period of time
(C<@timeout@> minutes unless overridden by the I<timeout> option.
By default, I<sudoers> uses a tty-based time stamp which means that
there is a separate time stamp for each of a user's login sessions.
The I<tty_tickets> option can be disabled to force the use of a
single time stamp for all of a user's sessions.
I<sudoers> can log both successful and unsuccessful attempts (as well
as errors) to syslog(3), a log file, or both. By default, I<sudoers>
will log via syslog(3) but this is changeable via the I<syslog>
and I<logfile> Defaults settings.
I<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 I<log_input> and I<log_output> Defaults flags as well as the
C<LOG_INPUT> and C<LOG_OUTPUT> command tags.
=head2 Command Environment
Since environment variables can influence program behavior, I<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 I<sudoers> can deal with environment variables.
By default, the I<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 F</etc/environment> file. On BSD systems, if the
I<use_loginclass> option is enabled, the environment is initialized
based on the I<path> and I<setenv> settings in F</etc/login.conf>.
The new environment contains the C<TERM>, C<PATH>, C<HOME>, C<MAIL>,
C<SHELL>, C<LOGNAME>, C<USER>, C<USERNAME> and C<SUDO_*> variables
in addition to variables from the invoking process permitted by the
I<env_check> and I<env_keep> options. This is effectively a whitelist
for environment variables.
If, however, the I<env_reset> option is disabled, any variables not
explicitly denied by the I<env_check> and I<env_delete> options are
inherited from the invoking process. In this case, I<env_check>
and I<env_delete> behave like a blacklist. Since it is not possible
to blacklist all potentially dangerous environment variables, use
of the default I<env_reset> behavior is encouraged.
In all cases, environment variables with a value beginning with
C<()> are removed as they could be interpreted as B<bash> functions.
The list of environment variables that B<sudo> allows or denies is
contained in the output of C<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 B<sudo>. Depending on the operating
system this may include C<_RLD*>, C<DYLD_*>, C<LD_*>, C<LDR_*>,
C<LIBPATH>, C<SHLIB_PATH>, and others. These type of variables are
removed from the environment before B<sudo> even begins execution
and, as such, it is not possible for B<sudo> to preserve them.
As a special case, if B<sudo>'s B<-i> option (initial login) is
specified, I<sudoers> will initialize the environment regardless
of the value of I<env_reset>. The I<DISPLAY>, I<PATH> and I<TERM>
variables remain unchanged; I<HOME>, I<MAIL>, I<SHELL>, I<USER>,
and I<LOGNAME> are set based on the target user. On AIX (and Linux
systems without PAM), the contents of F</etc/environment> are also
included. On BSD systems, if the I<use_loginclass> option is
enabled, the I<path> and I<setenv> variables in F</etc/login.conf>
are also applied. All other environment variables are removed.
Finally, if the I<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.
=head1 SUDOERS FILE FORMAT
The I<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 I<sudoers> grammar will be described below in Extended Backus-Naur
Form (EBNF). Don't despair if you don't know what EBNF is; it is
fairly simple, and the definitions below are annotated.
=head2 Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a language.
Each EBNF definition is made up of I<production rules>. E.g.,
symbol ::= definition | alternate1 | alternate2 ...
Each I<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.
=over 4
=item C<?>
Means that the preceding symbol (or group of symbols) is optional.
That is, it may appear once or not at all.
=item C<*>
Means that the preceding symbol (or group of symbols) may appear
zero or more times.
=item C<+>
Means that the preceding symbol (or group of symbols) may appear
one or more times.
=back
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).
=head2 Aliases
There are four kinds of aliases: C<User_Alias>, C<Runas_Alias>,
C<Host_Alias> and C<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 I<alias> definition is of the form
Alias_Type NAME = item1, item2, ...
where I<Alias_Type> is one of C<User_Alias>, C<Runas_Alias>, C<Host_Alias>,
or C<Cmnd_Alias>. A C<NAME> is a string of uppercase letters, numbers,
and underscore characters ('_'). A C<NAME> B<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 I<alias> member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A C<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
C<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 C<user name>, C<uid>, C<group>, C<gid>, C<netgroup>, C<nonunix_group>
or C<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 C<nonunix_group> and C<nonunix_gid> syntax depends on
the underlying group provider plugin (see the I<group_plugin>
description below). For instance, the QAS AD plugin supports the
following formats:
=over 4
=item *
Group in the same domain: "Group Name"
=item *
Group in any domain: "Group Name@FULLY.QUALIFIED.DOMAIN"
=item *
Group SID: "S-1-2-34-5678901234-5678901234-5678901234-567"
=back
Note that quotes around group names are optional. Unquoted strings
must use a backslash (\) to escape spaces and special characters.
See L<"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 C<Runas_List> is similar to a C<User_List> except that instead
of C<User_Alias>es it can contain C<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.E<nbsp>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 C<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,
B<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.E<nbsp>255.255.255.0 or ffff:ffff:ffff:ffff::),
or CIDR notation (number of bits, e.g.E<nbsp>24 or 64). A host name may
include shell-style wildcards (see the L<Wildcards> section below),
but unless the C<host name> command on your machine returns the fully
qualified host name, you'll need to use the I<fqdn> option for
wildcards to be useful. Note B<sudo> only inspects actual network
interfaces; this means that IP address 127.0.0.1 (localhost) will
never match. Also, the host name "localhost" will only match if
that is the actual host name, which is usually only the case for
non-networked systems.
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
commandname ::= file name |
file name args |
file name '""'
Cmnd ::= '!'* commandname |
'!'* directory |
'!'* "sudoedit" |
'!'* Cmnd_Alias
A C<Cmnd_List> is a list of one or more commandnames, directories, and other
aliases. A commandname is a fully qualified file name which may include
shell-style wildcards (see the L<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 C<""> to indicate that the command
may only be run B<without> command line arguments. A directory is a
fully qualified path name ending in a '/'. When you specify a directory
in a C<Cmnd_List>, the user will be able to run any file within that directory
(but not in any subdirectories therein).
If a C<Cmnd> has associated command line arguments, then the arguments
in the C<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 C<"sudoedit">
is used to permit a user to run B<sudo> with the B<-e> option (or
as B<sudoedit>). It may take command line arguments just as
a normal command does.
=head2 Defaults
Certain configuration options may be changed from their default
values at runtime via one or more C<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 C<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 B<flags>, B<integer> values, B<strings>, or B<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 (C<">) when they contain multiple words. Special
characters may be escaped with a backslash (C<\>).
Lists have two additional assignment operators, C<+=> and C<-=>.
These operators are used to add to and delete from a list respectively.
It is not an error to use the C<-=> 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 L<"SUDOERS OPTIONS"> for a list of supported Defaults parameters.
=head2 User Specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? 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 B<user specification> determines which commands a user may run
(and as what user) on specified hosts. By default, commands are
run as B<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:
=head2 Runas_Spec
A C<Runas_Spec> determines the user and/or the group that a command
may be run as. A fully-specified C<Runas_Spec> consists of two
C<Runas_List>s (as defined above) separated by a colon (':') and
enclosed in a set of parentheses. The first C<Runas_List> indicates
which users the command may be run as via B<sudo>'s B<-u> option.
The second defines a list of groups that can be specified via
B<sudo>'s B<-g> option. If both C<Runas_List>s are specified, the
command may be run with any combination of users and groups listed
in their respective C<Runas_List>s. If only the first is specified,
the command may be run as any user in the list but no B<-g> option
may be specified. If the first C<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 C<Runas_List>. If no
C<Runas_Spec> is specified the command may be run as B<root> and
no group may be specified.
A C<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 B<dgb> may run F</bin/ls>, F</bin/kill>, and
F</usr/bin/lprm> -- but only as B<operator>. E.g.,
$ sudo -u operator /bin/ls
It is also possible to override a C<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 B<dgb> is now allowed to run F</bin/ls> as B<operator>,
but F</bin/kill> and F</usr/bin/lprm> as B<root>.
We can extend this to allow B<dgb> to run C</bin/ls> with either
the user or group set to B<operator>:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill, \
/usr/bin/lprm
Note that while the group portion of the C<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 B<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 B<tcm>. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a C<Runas_Spec>, in
which case the user may select any combination of users and groups
via the B<-u> and B<-g> options. In this example:
alan ALL = (root, bin : operator, system) ALL
user B<alan> may run any command as either user root or bin,
optionally setting the group to operator or system.
=head2 SELinux_Spec
On systems with SELinux support, I<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 I<sudoers>. A role or type specified on the command line,
however, will supercede the values in I<sudoers>.
=head2 Tag_Spec
A command may have zero or more tags associated with it. There are
eight possible tag values, C<NOPASSWD>, C<PASSWD>, C<NOEXEC>,
C<EXEC>, C<SETENV>, C<NOSETENV>, C<LOG_INPUT>, C<NOLOG_INPUT>,
C<LOG_OUTPUT> and C<NOLOG_OUTPUT>. Once a tag is set on a C<Cmnd>,
subsequent C<Cmnd>s in the C<Cmnd_Spec_List>, inherit the tag unless
it is overridden by the opposite tag (i.e.: C<PASSWD> overrides
C<NOPASSWD> and C<NOEXEC> overrides C<EXEC>).
=head3 NOPASSWD and PASSWD
By default, B<sudo> requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
C<NOPASSWD> tag. Like a C<Runas_Spec>, the C<NOPASSWD> tag sets
a default for the commands that follow it in the C<Cmnd_Spec_List>.
Conversely, the C<PASSWD> tag can be used to reverse things.
For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user B<ray> to run F</bin/kill>, F</bin/ls>, and
F</usr/bin/lprm> as B<root> on the machine rushmore without
authenticating himself. If we only want B<ray> to be able to
run F</bin/kill> without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the C<PASSWD> tag has no effect on users who are
in the group specified by the I<exempt_group> option.
By default, if the C<NOPASSWD> tag is applied to any of the entries
for a user on the current host, he or she will be able to run
C<sudo -l> without a password. Additionally, a user may only run
C<sudo -v> without a password if the C<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.
=head3 NOEXEC and EXEC
If B<sudo> has been compiled with I<noexec> support and the underlying
operating system supports it, the C<NOEXEC> tag can be used to prevent
a dynamically-linked executable from running further commands itself.
In the following example, user B<aaron> may run F</usr/bin/more>
and F</usr/bin/vi> but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the L<Preventing Shell Escapes> section below for more details
on how C<NOEXEC> works and whether or not it will work on your system.
=head3 SETENV and NOSETENV
These tags override the value of the I<setenv> option on a per-command
basis. Note that if C<SETENV> has been set for a command, the user
may disable the I<env_reset> option from the command line via the
B<-E> option. Additionally, environment variables set on the command
line are not subject to the restrictions imposed by I<env_check>,
I<env_delete>, or I<env_keep>. As such, only trusted users should
be allowed to set variables in this manner. If the command matched
is B<ALL>, the C<SETENV> tag is implied for that command; this
default may be overridden by use of the C<NOSETENV> tag.
=head3 LOG_INPUT and NOLOG_INPUT
These tags override the value of the I<log_input> option on a
per-command basis. For more information, see the description of
I<log_input> in the L<"SUDOERS OPTIONS"> section below.
=head3 LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the I<log_output> option on a
per-command basis. For more information, see the description of
I<log_output> in the L<"SUDOERS OPTIONS"> section below.
=head2 Wildcards
B<sudo> allows shell-style I<wildcards> (aka meta or glob characters)
to be used in host names, path names and command line arguments in
the I<sudoers> file. Wildcard matching is done via the B<POSIX>
L<glob(3)> and L<fnmatch(3)> routines. Note that these are I<not>
regular expressions.
=over 8
=item C<*>
Matches any set of zero or more characters.
=item C<?>
Matches any single character.
=item C<[...]>
Matches any character in the specified range.
=item C<[!...]>
Matches any character B<not> in the specified range.
=item C<\x>
For any character "x", evaluates to "x". This is used to
escape special characters such as: "*", "?", "[", and "}".
=back
POSIX character classes may also be used if your system's L<glob(3)>
and L<fnmatch(3)> functions support them. However, because the
C<':'> character has special meaning in I<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 B<not> be matched by
wildcards used in the path name. When matching the command
line arguments, however, a slash B<does> get matched by
wildcards. This is to make a path like:
/usr/bin/*
match F</usr/bin/who> but not F</usr/bin/X11/xterm>.
=head2 Exceptions to wildcard rules
The following exceptions apply to the above rules:
=over 8
=item C<"">
If the empty string C<""> is the only command line argument in the
I<sudoers> entry it means that command is not allowed to be run
with B<any> arguments.
=back
=head2 Including other files from within sudoers
It is possible to include other I<sudoers> files from within the
I<sudoers> file currently being parsed using the C<#include> and
C<#includedir> directives.
This can be used, for example, to keep a site-wide I<sudoers> file
in addition to a local, per-machine file. For the sake of this
example the site-wide I<sudoers> will be F</etc/sudoers> and the
per-machine one will be F</etc/sudoers.local>. To include
F</etc/sudoers.local> from within F</etc/sudoers> we would use the
following line in F</etc/sudoers>:
=over 4
C<#include /etc/sudoers.local>
=back
When B<sudo> reaches this line it will suspend processing of the
current file (F</etc/sudoers>) and switch to F</etc/sudoers.local>.
Upon reaching the end of F</etc/sudoers.local>, the rest of
F</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 F</>), it must be located in the same directory as the
sudoers file it was included from. For example, if F</etc/sudoers>
contains the line:
=over 4
C<#include sudoers.local>
=back
the file that will be included is F</etc/sudoers.local>.
The file name may also include the C<%h> escape, signifying the short form
of the host name. I.e., if the machine's host name is "xerxes", then
C<#include /etc/sudoers.%h>
will cause B<sudo> to include the file F</etc/sudoers.xerxes>.
The C<#includedir> directive can be used to create a F<sudo.d>
directory that the system package manager can drop I<sudoers> rules
into as part of package installation. For example, given:
C<#includedir /etc/sudoers.d>
B<sudo> will read each file in F</etc/sudoers.d>, skipping file
names that end in C<~> or contain a C<.> character to avoid causing
problems with package manager or editor temporary/backup files.
Files are parsed in sorted lexical order. That is,
F</etc/sudoers.d/01_first> will be parsed before
F</etc/sudoers.d/10_second>. Be aware that because the sorting is
lexical, not numeric, F</etc/sudoers.d/1_whoops> would be loaded
B<after> F</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 C<#include>, B<visudo> will not
edit the files in a C<#includedir> directory unless one of them
contains a syntax error. It is still possible to run B<visudo>
with the C<-f> flag to edit the files directly.
=head2 Other special characters and reserved words
The pound sign ('#') is used to indicate a comment (unless it is
part of a #include directive or unless it occurs in the context of
a user name and is followed by one or more digits, in which case
it is treated as a uid). Both the comment character and any text
after it, up to the end of the line, are ignored.
The reserved word B<ALL> is a built-in I<alias> that always causes
a match to succeed. It can be used wherever one might otherwise
use a C<Cmnd_Alias>, C<User_Alias>, C<Runas_Alias>, or C<Host_Alias>.
You should not try to define your own I<alias> called B<ALL> as the
built-in alias will be used in preference to your own. Please note
that using B<ALL> can be dangerous since in a command context, it
allows the user to run B<any> command on the system.
An exclamation point ('!') can be used as a logical I<not> operator
both in an I<alias> and in front of a C<Cmnd>. This allows one to
exclude certain values. Note, however, that using a C<!> in
conjunction with the built-in C<ALL> alias to allow a user to
run "all but a few" commands rarely works as intended (see SECURITY
NOTES below).
Long lines can be continued with a backslash ('\') as the last
character on the line.
Whitespace between elements in a list as well as special syntactic
characters in a I<User Specification> ('=', ':', '(', ')') is optional.
The following characters must be escaped with a backslash ('\') when
used as part of a word (e.g.E<nbsp>a user name or host name):
'!', '=', ':', ',', '(', ')', '\'.
=head1 SUDOERS OPTIONS
B<sudo>'s behavior can be modified by C<Default_Entry> lines, as
explained earlier. A list of all supported Defaults parameters,
grouped by type, are listed below.
B<Boolean Flags>:
=over 16
=item always_set_home
If enabled, B<sudo> will set the C<HOME> environment variable to the
home directory of the target user (which is root unless the B<-u>
option is used). This effectively means that the B<-H> option is
always implied. Note that C<HOME> is already set when the the
I<env_reset> option is enabled, so I<always_set_home> is only
effective for configurations where either I<env_reset> is disabled
or C<HOME> is present in the I<env_keep> list.
This flag is I<off> by default.
=item authenticate
If set, users must authenticate themselves via a password (or other
means of authentication) before they may run commands. This default
may be overridden via the C<PASSWD> and C<NOPASSWD> tags.
This flag is I<on> by default.
=item closefrom_override
If set, the user may use B<sudo>'s B<-C> option which
overrides the default starting point at which B<sudo> begins
closing open file descriptors. This flag is I<off> by default.
=item compress_io
If set, and B<sudo> is configured to log a command's input or output,
the I/O logs will be compressed using B<zlib>. This flag is I<on>
by default when B<sudo> is compiled with B<zlib> support.
=item env_editor
If set, B<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 C<editor>
variable. B<visudo> will then only use the EDITOR or VISUAL if
they match a value specified in C<editor>. This flag is I<@env_editor@> by
default.
=item env_reset
If set, B<sudo> will run the command in a minimal environment
containing the C<TERM>, C<PATH>, C<HOME>, C<MAIL>, C<SHELL>,
C<LOGNAME>, C<USER>, C<USERNAME> and C<SUDO_*> variables. Any
variables in the caller's environment that match the C<env_keep>
and C<env_check> lists are then added, followed by any variables
present in the file specified by the I<env_file> option (if any).
The default contents of the C<env_keep> and C<env_check> lists are
displayed when B<sudo> is run by root with the I<-V> option. If
the I<secure_path> option is set, its value will be used for the
C<PATH> environment variable. This flag is I<@env_reset@> by
default.
=item fast_glob
Normally, B<sudo> uses the L<glob(3)> function to do shell-style
globbing when matching path names. However, since it accesses the
file system, L<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 (automounted). The I<fast_glob>
option causes B<sudo> to use the L<fnmatch(3)> function, which does
not access the file system to do its matching. The disadvantage
of I<fast_glob> is that it is unable to match relative path names
such as F<./ls> or F<../bin/ls>. This has security implications
when path names that include globbing characters are used with the
negation operator, C<'!'>, as such rules can be trivially bypassed.
As such, this option should not be used when I<sudoers> contains rules
that contain negated path names which include globbing characters.
This flag is I<off> by default.
=item fqdn
Set this flag if you want to put fully qualified host names in the
I<sudoers> file. I.e., instead of myhost you would use myhost.mydomain.edu.
You may still use the short form if you wish (and even mix the two).
Beware that turning on I<fqdn> requires B<sudo> to make DNS lookups
which may make B<sudo> unusable if DNS stops working (for example
if the machine is not plugged into the network). Also note that
you must use the host's official name as DNS knows it. That is,
you may not use a host alias (C<CNAME> entry) due to performance
issues and the fact that there is no way to get all aliases from
DNS. If your machine's host name (as returned by the C<hostname>
command) is already fully qualified you shouldn't need to set
I<fqdn>. This flag is I<@fqdn@> by default.
=item ignore_dot
If set, B<sudo> will ignore '.' or '' (current dir) in the C<PATH>
environment variable; the C<PATH> itself is not modified. This
flag is I<@ignore_dot@> by default.
=item ignore_local_sudoers
If set via LDAP, parsing of F<@sysconfdir@/sudoers> will be skipped.
This is intended for Enterprises that wish to prevent the usage of local
sudoers files so that only LDAP is used. This thwarts the efforts of
rogue operators who would attempt to add roles to F<@sysconfdir@/sudoers>.
When this option is present, F<@sysconfdir@/sudoers> does not even need to
exist. Since this option tells B<sudo> how to behave when no specific LDAP
entries have been matched, this sudoOption is only meaningful for the
C<cn=defaults> section. This flag is I<off> by default.
=item insults
If set, B<sudo> will insult users when they enter an incorrect
password. This flag is I<@insults@> by default.
=item log_host
If set, the host name will be logged in the (non-syslog) B<sudo> log file.
This flag is I<off> by default.
=item log_input
If set, B<sudo> will run the command in a I<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 I<iolog_dir>
option (F<@iolog_dir@> by default) using a unique session ID that
is included in the normal B<sudo> log line, prefixed with I<TSID=>.
The I<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 I<log_output> is all that is required.
=item log_output
If set, B<sudo> will run the command in a I<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 I<iolog_dir>
option (F<@iolog_dir@> by default) using a unique session ID that
is included in the normal B<sudo> log line, prefixed with I<TSID=>.
The I<iolog_file> option may be used to control the format of the
session ID.
Output logs may be viewed with the L<sudoreplay(8)> utility, which
can also be used to list or search the available logs.
=item log_year
If set, the four-digit year will be logged in the (non-syslog) B<sudo> log file.
This flag is I<off> by default.
=item long_otp_prompt
When validating with a One Time Password (OTP) scheme such as
B<S/Key> or B<OPIE>, a two-line prompt is used to make it easier
to cut and paste the challenge to a local window. It's not as
pretty as the default but some people find it more convenient. This
flag is I<@long_otp_prompt@> by default.
=item mail_always
Send mail to the I<mailto> user every time a users runs B<sudo>.
This flag is I<off> by default.
=item mail_badpass
Send mail to the I<mailto> user if the user running B<sudo> does not
enter the correct password. This flag is I<off> by default.
=item mail_no_host
If set, mail will be sent to the I<mailto> user if the invoking
user exists in the I<sudoers> file, but is not allowed to run
commands on the current host. This flag is I<@mail_no_host@> by default.
=item mail_no_perms
If set, mail will be sent to the I<mailto> user if the invoking
user is allowed to use B<sudo> but the command they are trying is not
listed in their I<sudoers> file entry or is explicitly denied.
This flag is I<@mail_no_perms@> by default.
=item mail_no_user
If set, mail will be sent to the I<mailto> user if the invoking
user is not in the I<sudoers> file. This flag is I<@mail_no_user@>
by default.
=item noexec
If set, all commands run via B<sudo> will behave as if the C<NOEXEC>
tag has been set, unless overridden by a C<EXEC> tag. See the
description of I<NOEXEC and EXEC> below as well as the L<Preventing Shell
Escapes> section at the end of this manual. This flag is I<off> by default.
=item path_info
Normally, B<sudo> will tell the user when a command could not be
found in their C<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 C<PATH>, B<sudo> will tell the user that they are not
allowed to run it, which can be confusing. This flag is I<@path_info@>
by default.
=item passprompt_override
The password prompt specified by I<passprompt> will normally only
be used if the password prompt provided by systems such as PAM matches
the string "Password:". If I<passprompt_override> is set, I<passprompt>
will always be used. This flag is I<off> by default.
=item preserve_groups
By default, B<sudo> will initialize the group vector to the list of
groups the target user is in. When I<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 I<off> by default.
=item pwfeedback
By default, B<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 B<sudo>
has hung at this point. When I<pwfeedback> is set, B<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 I<off> by default.
=item requiretty
If set, B<sudo> will only run when the user is logged in to a real
tty. When this flag is set, B<sudo> can only be run from a login
session and not via other means such as L<cron(8)> or cgi-bin scripts.
This flag is I<off> by default.
=item root_sudo
If set, root is allowed to run B<sudo> too. Disabling this prevents users
from "chaining" B<sudo> commands to get a root shell by doing something
like C<"sudo sudo /bin/sh">. Note, however, that turning off I<root_sudo>
will also prevent root from running B<sudoedit>.
Disabling I<root_sudo> provides no real additional security; it
exists purely for historical reasons.
This flag is I<@root_sudo@> by default.
=item rootpw
If set, B<sudo> will prompt for the root password instead of the password
of the invoking user. This flag is I<off> by default.
=item runaspw
If set, B<sudo> will prompt for the password of the user defined by the
I<runas_default> option (defaults to C<@runas_default@>) instead of the
password of the invoking user. This flag is I<off> by default.
=item set_home
If enabled and B<sudo> is invoked with the B<-s> option the C<HOME>
environment variable will be set to the home directory of the target
user (which is root unless the B<-u> option is used). This effectively
makes the B<-s> option imply B<-H>. Note that C<HOME> is already
set when the the I<env_reset> option is enabled, so I<set_home> is
only effective for configurations where either I<env_reset> is disabled
or C<HOME> is present in the I<env_keep> list.
This flag is I<off> by default.
=item set_logname
Normally, B<sudo> will set the C<LOGNAME>, C<USER> and C<USERNAME>
environment variables to the name of the target user (usually root
unless the B<-u> option is given). However, since some programs
(including the RCS revision control system) use C<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 I<env_reset> option has not been disabled,
entries in the I<env_keep> list will override the value of
I<set_logname>. This flag is I<on> by default.
=item set_utmp
When enabled, B<sudo> will create an entry in the utmp (or utmpx)
file when a pseudo-tty is allocated. A pseudo-tty is allocated by
B<sudo> when the I<log_input>, I<log_output> or I<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 I<on> by default.
=item setenv
Allow the user to disable the I<env_reset> option from the command
line via the B<-E> option. Additionally, environment variables set
via the command line are not subject to the restrictions imposed
by I<env_check>, I<env_delete>, or I<env_keep>. As such, only
trusted users should be allowed to set variables in this manner.
This flag is I<off> by default.
=item shell_noargs
If set and B<sudo> is invoked with no arguments it acts as if the
B<-s> option had been given. That is, it runs a shell as root (the
shell is determined by the C<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 I<off> by default.
=item stay_setuid
Normally, when B<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 B<sudo> act as a setuid
wrapper. This can be useful on systems that disable some potentially
dangerous functionality when a program is run setuid. This option
is only effective on systems with either the setreuid() or setresuid()
function. This flag is I<off> by default.
=item targetpw
If set, B<sudo> will prompt for the password of the user specified
by the B<-u> option (defaults to C<root>) instead of the password
of the invoking user. In addition, the timestamp 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 B<-u> option. This flag is I<off> by default.
=item tty_tickets
If set, users must authenticate on a per-tty basis. With this flag
enabled, B<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
I<@tty_tickets@> by default.
=item umask_override
If set, B<sudo> will set the umask as specified by I<sudoers> without
modification. This makes it possible to specify a more permissive
umask in I<sudoers> than the user's own umask and matches historical
behavior. If I<umask_override> is not set, B<sudo> will set the
umask to be the union of the user's umask and what is specified in
I<sudoers>. This flag is I<@umask_override@> by default.
=item use_loginclass
If set, B<sudo> will apply the defaults specified for the target user's
login class if one exists. Only available if B<sudo> is configured with
the --with-logincap option. This flag is I<off> by default.
=item use_pty
If set, B<sudo> will run the command in a pseudo-pty even if no I/O
logging is being gone. A malicious program run under B<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 I<off> by default.
=item utmp_runas
If set, B<sudo> will store the name of the runas user when updating
the utmp (or utmpx) file. By default, B<sudo> stores the name of
the invoking user. This flag is I<off> by default.
=item visiblepw
By default, B<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 I<visiblepw> flag is set, B<sudo> will prompt for a password
even when it would be visible on the screen. This makes it possible
to run things like C<"rsh somehost sudo ls"> since L<rsh(1)> does
not allocate a tty. This flag is I<off> by default.
=back
B<Integers>:
=over 16
=item closefrom
Before it executes a command, B<sudo> will close all open file
descriptors other than standard input, standard output and standard
error (ie: file descriptors 0-2). The I<closefrom> option can be used
to specify a different file descriptor at which to start closing.
The default is C<3>.
=item passwd_tries
The number of tries a user gets to enter his/her password before
B<sudo> logs the failure and exits. The default is C<@passwd_tries@>.
=back
B<Integers that can be used in a boolean context>:
=over 16
=item loglinelen
Number of characters per line for the file log. This value is used
to decide when to wrap lines for nicer log files. This has no
effect on the syslog log file, only the file log. The default is
C<@loglen@> (use 0 or negate the option to disable word wrap).
=item passwd_timeout
Number of minutes before the B<sudo> password prompt times out, or
C<0> for no timeout. The timeout may include a fractional component
if minute granularity is insufficient, for example C<2.5>. The
default is C<@password_timeout@>.
=item timestamp_timeout
Number of minutes that can elapse before B<sudo> will ask for a
passwd again. The timeout may include a fractional component if
minute granularity is insufficient, for example C<2.5>. The default
is C<@timeout@>. Set this to C<0> to always prompt for a password.
If set to a value less than C<0> the user's timestamp will never
expire. This can be used to allow users to create or delete their
own timestamps via C<sudo -v> and C<sudo -k> respectively.
=item umask
Umask to use when running the command. Negate this option or set
it to 0777 to preserve the user's umask. The actual umask that is
used will be the union of the user's umask and the value of the
I<umask> option, which defaults to C<@sudo_umask@>. This guarantees
that B<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 I<sudoers>.
=back
B<Strings>:
=over 16
=item badpass_message
Message that is displayed if a user enters an incorrect password.
The default is C<@badpass_message@> unless insults are enabled.
=item editor
A colon (':') separated list of editors allowed to be used with
B<visudo>. B<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 C<"@editor@">.
=item iolog_dir
The top-level directory to use when constructing the path name for
the input/output log directory. Only used if the I<log_input> or
I<log_output> options are enabled or when the C<LOG_INPUT> or
C<LOG_OUTPUT> tags are present for a command. The session sequence
number, if any, is stored in the directory.
The default is C<"@iolog_dir@">.
The following percent (`C<%>') escape sequences are supported:
=over 4
=item C<%{seq}>
expanded to a monotonically increasing base-36 sequence number, such as 0100A5,
where every two digits are used to form a new directory, e.g. F<01/00/A5>
=item C<%{user}>
expanded to the invoking user's login name
=item C<%{group}>
expanded to the name of the invoking user's real group ID
=item C<%{runas_user}>
expanded to the login name of the user the command will
be run as (e.g. root)
=item C<%{runas_group}>
expanded to the group name of the user the command will
be run as (e.g. wheel)
=item C<%{hostname}>
expanded to the local host name without the domain name
=item C<%{command}>
expanded to the base name of the command being run
=back
In addition, any escape sequences supported by the system's strftime()
function will be expanded.
To include a literal `C<%>' character, the string `C<%%>' should
be used.
=item iolog_file
The path name, relative to I<iolog_dir>, in which to store input/output
logs when the I<log_input> or I<log_output> options are enabled or
when the C<LOG_INPUT> or C<LOG_OUTPUT> tags are present for a command.
Note that I<iolog_file> may contain directory components.
The default is C<"%{seq}">.
See the I<iolog_dir> option above for a list of supported percent
(`C<%>') escape sequences.
In addition to the escape sequences, path names that end in six or
more C<X>s will have the C<X>s replaced with a unique combination
of digits and letters, similar to the mktemp() function.
=item mailsub
Subject of the mail sent to the I<mailto> user. The escape C<%h>
will expand to the host name of the machine.
Default is C<@mailsub@>.
=item noexec_file
This option is no longer supported. The path to the noexec file
should now be set in the F<@sysconfdir@/sudo.conf> file.
=item passprompt
The default prompt to use when asking for a password; can be overridden
via the B<-p> option or the C<SUDO_PROMPT> environment variable.
The following percent (`C<%>') escape sequences are supported:
=over 4
=item C<%H>
expanded to the local host name including the domain name
(only if the machine's host name is fully qualified or the I<fqdn>
option is set)
=item C<%h>
expanded to the local host name without the domain name
=item C<%p>
expanded to the user whose password is being asked for (respects the
I<rootpw>, I<targetpw> and I<runaspw> flags in I<sudoers>)
=item C<%U>
expanded to the login name of the user the command will
be run as (defaults to root)
=item C<%u>
expanded to the invoking user's login name
=item C<%%>
two consecutive C<%> characters are collapsed into a single C<%> character
=back
The default value is C<@passprompt@>.
=item role
The default SELinux role to use when constructing a new security
context to run the command. The default role may be overridden on
a per-command basis in I<sudoers> or via command line options.
This option is only available whe B<sudo> is built with SELinux support.
=item runas_default
The default user to run commands as if the B<-u> option is not specified
on the command line. This defaults to C<@runas_default@>.
=item syslog_badpri
Syslog priority to use when user authenticates unsuccessfully.
Defaults to C<@badpri@>.
The following syslog priorities are supported: B<alert>, B<crit>,
B<debug>, B<emerg>, B<err>, B<info>, B<notice>, and B<warning>.
=item syslog_goodpri
Syslog priority to use when user authenticates successfully.
Defaults to C<@goodpri@>.
See L<syslog_badpri> for the list of supported syslog priorities.
=item sudoers_locale
Locale to use when parsing the sudoers file, logging commands, and
sending email. Note that changing the locale may affect how sudoers
is interpreted. Defaults to C<"C">.
=item timestampdir
The directory in which B<sudo> stores its timestamp files.
The default is F<@timedir@>.
=item timestampowner
The owner of the timestamp directory and the timestamps stored therein.
The default is C<root>.
=item type
The default SELinux type to use when constructing a new security
context to run the command. The default type may be overridden on
a per-command basis in I<sudoers> or via command line options.
This option is only available whe B<sudo> is built with SELinux support.
=back
B<Strings that can be used in a boolean context>:
=over 12
=item env_file
The I<env_file> option specifies the fully qualified path to a
file containing variables to be set in the environment of the program
being run. Entries in this file should either be of the form
C<VARIABLE=value> or C<export VARIABLE=value>. The value may
optionally be surrounded by single or double quotes. Variables in
this file are subject to other B<sudo> environment settings such
as I<env_keep> and I<env_check>.
=item exempt_group
Users in this group are exempt from password and PATH requirements.
The group name specified should not include a C<%> prefix.
This is not set by default.
=item group_plugin
A string containing a I<sudoers> group plugin with optional arguments.
This can be used to implement support for the C<nonunix_group>
syntax described earlier. The string should consist of the plugin
path, either fully-qualified or relative to the F<@prefix@/libexec>
directory, followed by any configuration arguments the plugin
requires. These arguments (if any) will be passed to the plugin's
initialization function. If arguments are present, the string must
be enclosed in double quotes (C<">).
For example, given F</etc/sudo-group>, a group file in Unix group
format, the sample group plugin can be used:
Defaults group_plugin="sample_group.so /etc/sudo-group"
For more information see L<sudo_plugin(5)>.
=item lecture
This option controls when a short lecture will be printed along with
the password prompt. It has the following possible values:
=over 8
=item always
Always lecture the user.
=item never
Never lecture the user.
=item once
Only lecture the user the first time they run B<sudo>.
=back
If no value is specified, a value of I<once> is implied.
Negating the option results in a value of I<never> being used.
The default value is I<@lecture@>.
=item lecture_file
Path to a file containing an alternate B<sudo> lecture that will
be used in place of the standard lecture if the named file exists.
By default, B<sudo> uses a built-in lecture.
=item listpw
This option controls when a password will be required when a
user runs B<sudo> with the B<-l> option. It has the following possible values:
=over 8
=item all
All the user's I<sudoers> entries for the current host must have
the C<NOPASSWD> flag set to avoid entering a password.
=item always
The user must always enter a password to use the B<-l> option.
=item any
At least one of the user's I<sudoers> entries for the current host
must have the C<NOPASSWD> flag set to avoid entering a password.
=item never
The user need never enter a password to use the B<-l> option.
=back
If no value is specified, a value of I<any> is implied.
Negating the option results in a value of I<never> being used.
The default value is I<any>.
=item logfile
Path to the B<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, B<sudo> logs via syslog.
=item mailerflags
Flags to use when invoking mailer. Defaults to B<-t>.
=item mailerpath
Path to mail program used to send warning mail.
Defaults to the path to sendmail found at configure time.
=item mailfrom
Address to use for the "from" address when sending warning and error
mail. The address should be enclosed in double quotes (C<">) to
protect against B<sudo> interpreting the C<@> sign. Defaults to
the name of the user running B<sudo>.
=item mailto
Address to send warning and error mail to. The address should
be enclosed in double quotes (C<">) to protect against B<sudo>
interpreting the C<@> sign. Defaults to C<@mailto@>.
=item secure_path
Path used for every command run from B<sudo>. If you don't trust the
people running B<sudo> to have a sane C<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
I<exempt_group> option are not affected by I<secure_path>.
This option is @secure_path@ by default.
=item syslog
Syslog facility if syslog is being used for logging (negate to
disable syslog logging). Defaults to C<@logfac@>.
The following syslog facilities are supported: B<authpriv> (if your
OS supports it), B<auth>, B<daemon>, B<user>, B<local0>, B<local1>,
B<local2>, B<local3>, B<local4>, B<local5>, B<local6>, and B<local7>.
=item verifypw
This option controls when a password will be required when a user runs
B<sudo> with the B<-v> option. It has the following possible values:
=over 8
=item all
All the user's I<sudoers> entries for the current host must have
the C<NOPASSWD> flag set to avoid entering a password.
=item always
The user must always enter a password to use the B<-v> option.
=item any
At least one of the user's I<sudoers> entries for the current host
must have the C<NOPASSWD> flag set to avoid entering a password.
=item never
The user need never enter a password to use the B<-v> option.
=back
If no value is specified, a value of I<all> is implied.
Negating the option results in a value of I<never> being used.
The default value is I<all>.
=back
B<Lists that can be used in a boolean context>:
=over 16
=item env_check
Environment variables to be removed from the user's environment if
the variable's value contains C<%> or C</> 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 C<=>, C<+=>, C<-=>, and C<!> operators respectively. Regardless
of whether the C<env_reset> option is enabled or disabled, variables
specified by C<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 B<sudo> is run by root with
the I<-V> option.
=item env_delete
Environment variables to be removed from the user's environment
when the I<env_reset> option is not in effect. 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 C<=>, C<+=>, C<-=>, and C<!> operators
respectively. The default list of environment variables to remove
is displayed when B<sudo> is run by root with the I<-V> option.
Note that many operating systems will remove potentially dangerous
variables from the environment of any setuid process (such as
B<sudo>).
=item env_keep
Environment variables to be preserved in the user's environment
when the I<env_reset> option is in effect. This allows fine-grained
control over the environment B<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 C<=>, C<+=>, C<-=>, and
C<!> operators respectively. The default list of variables to keep
is displayed when B<sudo> is run by root with the I<-V> option.
=back
=head1 SUDO.CONF
The F<@sysconfdir@/sudo.conf> file determines which plugins the
B<sudo> front end will load. If no F<@sysconfdir@/sudo.conf> file
is present, or it contains no C<Plugin> lines, B<sudo> will use the
I<sudoers> security policy and I/O logging, which corresponds to
the following F<@sysconfdir@/sudo.conf> file.
#
# Default @sysconfdir@/sudo.conf file
#
# Format:
# Plugin plugin_name plugin_path plugin_options ...
# Path askpass /path/to/askpass
# Path noexec /path/to/sudo_noexec.so
# Debug sudo /var/log/sudo_debug all@warn
# Set disable_coredump true
#
# The plugin_path is relative to @prefix@/libexec unless
# fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
# that contains the plugin interface structure.
# The plugin_options are optional.
#
Plugin policy_plugin sudoers.so
Plugin io_plugin sudoers.so
=head2 PLUGIN OPTIONS
Starting with B<sudo> 1.8.5 it is possible to pass options to the
I<sudoers> plugin. Options may be listed after the path to the
plugin (i.e. after F<sudoers.so>); multiple options should be
space-separated. For example:
Plugin sudoers_policy sudoers.so sudoers_file=/etc/sudoers sudoers_uid=0 sudoers_gid=0 sudoers_mode=0440
The following plugin options are supported:
=over 10
=item sudoers_file=pathname
The I<sudoers_file> option can be used to override the default path
to the I<sudoers> file.
=item sudoers_uid=uid
The I<sudoers_uid> option can be used to override the default owner
of the sudoers file. It should be specified as a numeric user ID.
=item sudoers_gid=gid
The I<sudoers_gid> option can be used to override the default group
of the sudoers file. It should be specified as a numeric group ID.
=item sudoers_mode=mode
The I<sudoers_mode> option can be used to override the default file
mode for the sudoers file. It should be specified as an octal value.
=back
=head2 DEBUG FLAGS
Versions 1.8.4 and higher of the I<sudoers> plugin supports a
debugging framework that can help track down what the plugin is
doing internally if there is a problem. This can be configured in
the F<@sysconfdir@/sudo.conf> file as described in L<sudo(8)>.
The I<sudoers> plugin uses the same debug flag format as B<sudo>
itself: I<subsystem>@I<priority>.
The priorities used by I<sudoers>, in order of decreasing severity,
are: I<crit>, I<err>, I<warn>, I<notice>, I<diag>, I<info>, I<trace>
and I<debug>. Each priority, when specified, also includes all
priorities higher than it. For example, a priority of I<notice>
would include debug messages logged at I<notice> and higher.
The following subsystems are used by I<sudoers>:
=over 10
=item I<alias>
C<User_Alias>, C<Runas_Alias>, C<Host_Alias> and C<Cmnd_Alias> processing
=item I<all>
matches every subsystem
=item I<audit>
BSM and Linux audit code
=item I<auth>
user authentication
=item I<defaults>
I<sudoers> I<Defaults> settings
=item I<env>
environment handling
=item I<ldap>
LDAP-based sudoers
=item I<logging>
logging support
=item I<match>
matching of users, groups, hosts and netgroups in I<sudoers>
=item I<netif>
network interface handling
=item I<nss>
network service switch handling in I<sudoers>
=item I<parser>
I<sudoers> file parsing
=item I<perms>
permission setting
=item I<plugin>
The equivalent of I<main> for the plugin.
=item I<pty>
pseudo-tty related code
=item I<rbtree>
redblack tree internals
=item I<util>
utility functions
=back
=head1 FILES
=over 24
=item F<@sysconfdir@/sudo.conf>
Sudo front end configuration
=item F<@sysconfdir@/sudoers>
List of who can run what
=item F</etc/group>
Local groups file
=item F</etc/netgroup>
List of network groups
=item F<@iolog_dir@>
I/O log files
=item F<@timedir@>
Directory containing time stamps for the I<sudoers> security policy
=item F</etc/environment>
Initial environment for B<-i> mode on AIX and Linux systems
=back
=head1 EXAMPLES
Below are example I<sudoers> entries. Admittedly, some of
these are a bit contrived. First, we allow a few environment
variables to pass and then define our I<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
B<sudo> to log via L<syslog(3)> using the I<auth> facility in all
cases. We don't want to subject the full time staff to the B<sudo>
lecture, user B<millert> need not give a password, and we don't
want to reset the C<LOGNAME>, C<USER> or C<USERNAME> environment
variables when running commands as root. Additionally, on the
machines in the I<SERVERS> C<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 C<Cmnd_Alias>
(F</usr/bin/more>, F</usr/bin/pg> and F</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 I<User specification> is the part that actually determines who may
run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let B<root> and any user in group B<wheel> run any command on any
host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (B<millert>, B<mikef>, and B<dowdy>) may run any
command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (B<bostley>, B<jwfox>, and B<crawl>) may run any
command on any host but they must authenticate themselves first
(since the entry lacks the C<NOPASSWD> tag).
jack CSNETS = ALL
The user B<jack> may run any command on the machines in the I<CSNETS> alias
(the networks C<128.138.243.0>, C<128.138.204.0>, and C<128.138.242.0>).
Of those networks, only C<128.138.204.0> has an explicit netmask (in
CIDR notation) indicating it is a class C network. For the other
networks in I<CSNETS>, the local machine's netmask will be used
during matching.
lisa CUNETS = ALL
The user B<lisa> may run any command on any host in the I<CUNETS> alias
(the class B network C<128.138.0.0>).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The B<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 F</usr/oper/bin/>.
joe ALL = /usr/bin/su operator
The user B<joe> may only L<su(1)> to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the B<opers> group may run commands in F</usr/sbin/> as themselves
with any group in the I<ADMINGRP> C<Runas_Alias> (the B<adm> and B<oper>
groups).
The user B<pete> is allowed to change anyone's password except for
root on the I<HPPA> machines. Note that this assumes L<passwd(1)>
does not take multiple user names on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user B<bob> may run anything on the I<SPARC> and I<SGI> machines
as any user listed in the I<OP> C<Runas_Alias> (B<root> and B<operator>).
jim +biglab = ALL
The user B<jim> may run any command on machines in the I<biglab> netgroup.
B<sudo> knows that "biglab" is a netgroup due to the '+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the B<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 B<fred> can run commands as any user in the I<DB> C<Runas_Alias>
(B<oracle> or B<sybase>) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the I<ALPHA> machines, user B<john> may su to anyone except root
but he is not allowed to specify any options to the L<su(1)> command.
jen ALL, !SERVERS = ALL
The user B<jen> may run any command on any machine except for those
in the I<SERVERS> C<Host_Alias> (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the I<SERVERS> C<Host_Alias>, B<jill> may run
any commands in the directory F</usr/bin/> except for those commands
belonging to the I<SU> and I<SHELLS> C<Cmnd_Aliases>.
steve CSNETS = (operator) /usr/local/op_commands/
The user B<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, B<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 I<WEBMASTERS> C<User_Alias> (will,
wendy, and wim), may run any command as user www (which owns the
web pages) or simply L<su(1)> to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
C<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.
=head1 SECURITY NOTES
=head2 Limitations of the '!' operator
It is generally not effective to "subtract" commands from C<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 B<bill> from running the commands listed in
I<SU> or I<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 C<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.
=head2 Security implications of I<fast_glob>
If the I<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
L<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 I<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 B<john> can still run C</usr/bin/passwd root> if I<fast_glob> is
enabled by changing to F</usr/bin> and running C<./passwd root> instead.
=head2 Preventing Shell Escapes
Once B<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 B<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:
=over 10
=item restrict
Avoid giving users access to commands that allow the user to run
arbitrary commands. Many editors have a restricted mode where shell
escapes are disabled, though B<sudoedit> is a better solution to
running editors via B<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.
=item noexec
Many systems that support shared libraries have the ability to
override default library functions by pointing an environment
variable (usually C<LD_PRELOAD>) to an alternate shared library.
On such systems, B<sudo>'s I<noexec> functionality can be used to
prevent a program run by B<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 I<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
C<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 C<LD_PRELOAD> is supported.
On Solaris 10 and higher, I<noexec> uses Solaris privileges instead
of the C<LD_PRELOAD> environment variable.
To enable I<noexec> for a command, use the C<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 B<aaron> to run F</usr/bin/more> and F</usr/bin/vi>
with I<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 I<noexec> you
can always just try it out and check whether shell escapes work
when I<noexec> is enabled.
=back
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
B<sudoedit>.
=head2 Time stamp file checks
I<sudoers> will check the ownership of its time stamp directory
(F<@timedir@> 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. On systems that allow non-root users to give away files via
L<chown(2)>, if the time stamp directory is located in a world-writable
directory (e.g., F</tmp>), it is possible for a user to create the
time stamp directory before B<sudo> is run. However, because
I<sudoers> checks the ownership and mode of the directory and its
contents, the only damage that can be done is to "hide" files by
putting them in the time stamp dir. This is unlikely to happen
since once the time stamp dir is owned by root and inaccessible by
any other user, the user placing files there would be unable to get
them back out.
I<sudoers> will not honor time stamps set far in the future. Time
stamps with a date greater than current_time + 2 * C<TIMEOUT> will
be ignored and sudo will log and complain. This is done to keep a
user from creating his/her own time stamp with a bogus date on
systems that allow users to give away files if the time stamp directory
is located in a world-writable directory.
On systems where the boot time is available, I<sudoers> will ignore
time stamps that date from before the machine booted.
Since time stamp files live in the file system, they can outlive a
user's login session. As a result, a user may be able to login,
run a command with B<sudo> after authenticating, logout, login
again, and run B<sudo> without authenticating so long as the time
stamp file's modification time is within C<@timeout@> minutes (or
whatever the timeout is set to in I<sudoers>). When the I<tty_tickets>
option is enabled, the time stamp has per-tty granularity but still
may outlive the user's session. On Linux systems where the devpts
filesystem is used, Solaris systems with the devices filesystem,
as well as other systems that utilize a devfs filesystem that
monotonically increase the inode number of devices as they are
created (such as Mac OS X), I<sudoers> is able to determine when a
tty-based time stamp file is stale and will ignore it. Administrators
should not rely on this feature as it is not universally available.
=head1 SEE ALSO
L<rsh(1)>, L<su(1)>, L<fnmatch(3)>, L<glob(3)>, L<mktemp(3)>, L<strftime(3)>,
L<sudoers.ldap(5)>, L<sudo_plugin(8)>, L<sudo(8)>, L<visudo(8)>
=head1 CAVEATS
The I<sudoers> file should B<always> be edited by the B<visudo>
command which locks the file and does grammatical checking. It is
imperative that I<sudoers> be free of syntax errors since B<sudo>
will not run with a syntactically incorrect I<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 C<hostname> command or use the I<fqdn> option in
I<sudoers>.
=head1 BUGS
If you feel you have found a bug in B<sudo>, please submit a bug report
at http://www.sudo.ws/sudo/bugs/
=head1 SUPPORT
Limited free support is available via the sudo-users mailing list,
see http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
search the archives.
=head1 DISCLAIMER
B<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 B<sudo> or http://www.sudo.ws/sudo/license.html
for complete details.
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