Manual Page - sudoers(5)
Manual Reference Pages - SUDOERS (5)
NAME
sudoers - list of which users may execute what
CONTENTS
DESCRIPTION
The sudoers file is composed of two types of entries: aliases
(basically variables) and user specifications (which specify who
may run what).
When multiple entries match for a user, they are applied in order.
Where there are multiple matches, the last match is used (which is
not necessarily the most specific match).
The sudoers grammar will be described below in Extended Backus-Naur
Form (EBNF). Don’t despair if you don’t know what EBNF is; it is
fairly simple, and the definitions below are annotated.
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 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.
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?
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Means that the preceding symbol (or group of symbols) is optional.
That is, it may appear once or not at all.
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*
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Means that the preceding symbol (or group of symbols) may appear
zero or more times.
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+
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Means that the preceding symbol (or group of symbols) may appear
one or more times.
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Parentheses may be used to group symbols together. For clarity,
we will use single quotes (’’) to designate what is a verbatim character
string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias,
Host_Alias and Cmnd_Alias.
Alias ::= ’User_Alias’ User_Alias (’:’ User_Alias)* |
’Runas_Alias’ Runas_Alias (’:’ Runas_Alias)* |
’Host_Alias’ Host_Alias (’:’ Host_Alias)* |
’Cmnd_Alias’ Cmnd_Alias (’:’ Cmnd_Alias)*
User_Alias ::= NAME ’=’ User_List
Runas_Alias ::= NAME ’=’ Runas_List
Host_Alias ::= NAME ’=’ Host_List
Cmnd_Alias ::= NAME ’=’ Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias,
or Cmnd_Alias. A NAME is a string of uppercase letters, numbers,
and underscore characters (’_’). A NAME must start with an
uppercase letter. It is possible to put several alias definitions
of the same type on a single line, joined by a colon (’:’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ’,’ User_List
User ::= ’!’* username |
’!’* ’%’group |
’!’* ’+’netgroup |
’!’* User_Alias
A User_List is made up of one or more usernames, system groups
(prefixed with ’%’), netgroups (prefixed with ’+’) and other aliases.
Each list item may be prefixed with one or more ’!’ operators.
An odd number of ’!’ operators negate the value of the item; an even
number just cancel each other out.
Runas_List ::= Runas_User |
Runas_User ’,’ Runas_List
Runas_User ::= ’!’* username |
’!’* ’#’uid |
’!’* ’%’group |
’!’* +netgroup |
’!’* Runas_Alias
A Runas_List is similar to a User_List except that it can
also contain uids (prefixed with ’#’) and instead of User_Aliases
it can contain Runas_Aliases. Note that usernames and groups
are matched as strings. In other words, two users (groups) with
the same uid (gid) are considered to be distinct. If you wish to
match all usernames with the same uid (e.g. root and toor), you
can use a uid instead (#0 in the example given).
Host_List ::= Host |
Host ’,’ Host_List
Host ::= ’!’* hostname |
’!’* ip_addr |
’!’* network(/netmask)? |
’!’* ’+’netgroup |
’!’* Host_Alias
A Host_List is made up of one or more hostnames, IP addresses,
network numbers, netgroups (prefixed with ’+’) and other aliases.
Again, the value of an item may be negated with the ’!’ operator.
If you do not specify a netmask along with the network number,
sudo will query each of the local host’s network interfaces and,
if the network number corresponds to one of the hosts’s network
interfaces, the corresponding netmask will be used. The netmask
may be specified either in dotted quad notation (e.g. 255.255.255.0)
or CIDR notation (number of bits, e.g. 24). A hostname may
include shell-style wildcards (see the Wildcards section below),
but unless the hostname command on your machine returns the fully
qualified hostname, you’ll need to use the fqdn option for
wildcards to be useful.
Cmnd_List ::= Cmnd |
Cmnd ’,’ Cmnd_List
commandname ::= filename |
filename args |
filename ’""’
Cmnd ::= ’!’* commandname |
’!’* directory |
’!’* "sudoedit" |
’!’* Cmnd_Alias
A Cmnd_List is a list of one or more commandnames, directories, and other
aliases. A commandname is a fully qualified filename which may include
shell-style wildcards (see the Wildcards section below). A simple
filename allows the user to run the command with any arguments he/she
wishes. However, you may also specify command line arguments (including
wildcards). Alternately, you can specify "" to indicate that the command
may only be run without command line arguments. A directory is a
fully qualified pathname ending in a ’/’. When you specify a directory
in a Cmnd_List, the user will be able to run any file within that directory
(but not in any subdirectories therein).
If a Cmnd has associated command line arguments, then the arguments
in the Cmnd must match exactly those given by the user on the command line
(or match the wildcards if there are any). Note that the following
characters must be escaped with a ’\’ if they are used in command
arguments: ’,’, ’:’, ’=’, ’\’. The special command "sudoedit"
is used to permit a user to run sudo with the -e flag (or
as sudoedit). It may take command line arguments just as
a normal command does.
Defaults
Certain configuration options may be changed from their default
values at runtime via one or more Default_Entry lines. These
may affect all users on any host, all users on a specific host, a
specific user, or commands being run as a specific user.
Default_Type ::= ’Defaults’ |
’Defaults’ ’@’ Host |
’Defaults’ ’:’ User |
’Defaults’ ’>’ RunasUser
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ’,’ Parameter_List
Parameter ::= Parameter ’=’ Value |
Parameter ’+=’ Value |
Parameter ’-=’ Value |
’!’* Parameter
Parameters may be flags, integer values, strings, or lists.
Flags are implicitly boolean and can be turned off via the ’!’
operator. Some integer, string and list parameters may also be
used in a boolean context to disable them. Values may be enclosed
in double quotes (") when they contain multiple words. Special
characters may be escaped with a backslash (\).
Lists have two additional assignment operators, += and -=.
These operators are used to add to and delete from a list respectively.
It is not an error to use the -= operator to remove an element
that does not exist in a list.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User Specification
User_Spec ::= User_List Host_List ’=’ Cmnd_Spec_List \
(’:’ Host_List ’=’ Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ’,’ Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Tag_Spec* Cmnd
Runas_Spec ::= ’(’ Runas_List ’)’
Tag_Spec ::= (’NOPASSWD:’ | ’PASSWD:’ | ’NOEXEC:’ | ’EXEC:’ |
’SETENV:’ | ’NOSETENV:’)
A user specification determines which commands a user may run
(and as what user) on specified hosts. By default, commands are
run as root, but this can be changed on a per-command basis.
Let’s break that down into its constituent parts:
Runas_Spec
A Runas_Spec is simply a Runas_List (as defined above)
enclosed in a set of parentheses. If you do not specify a
Runas_Spec in the user specification, a default Runas_Spec
of root will be used. A Runas_Spec sets the default for
commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and
/usr/bin/lprm — but only as operator. E.g.,
$ sudo -u operator /bin/ls.
It is also possible to override a Runas_Spec later on in an
entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator,
but /bin/kill and /usr/bin/lprm as root.
Tag_Spec
A command may have zero or more tags associated with it. There are
six possible tag values, NOPASSWD, PASSWD, NOEXEC, EXEC,
SETENV and NOSETENV.
Once a tag is set on a Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit the tag unless it is overridden by the
opposite tag (i.e.: PASSWD overrides NOPASSWD and NOEXEC
overrides EXEC).
NOPASSWD and PASSWD
By default, sudo requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets
a default for the commands that follow it in the Cmnd_Spec_List.
Conversely, the PASSWD tag can be used to reverse things.
For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and
/usr/bin/lprm as root on the machine rushmore as root without
authenticating himself. If we only want ray to be able to
run /bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are
in the group specified by the exempt_group option.
By default, if the NOPASSWD tag is applied to any of the entries
for a user on the current host, he or she will be able to run
sudo -l without a password. Additionally, a user may only run
sudo -v without a password if the NOPASSWD tag is present
for all a user’s entries that pertain to the current host.
This behavior may be overridden via the verifypw and listpw options.
NOEXEC and EXEC
If sudo has been compiled with noexec support and the underlying
operating system supports it, the NOEXEC tag can be used to prevent
a dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more
and /usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the PREVENTING SHELL ESCAPES section below for more details
on how NOEXEC works and whether or not it will work on your system.
SETENV and NOSETENV
These tags override the value of the setenv option on a per-command
basis. Note that if SETENV has been set for a command, any
environment variables set on the command line way are not subject
to the restrictions imposed by env_check, env_delete, or
env_keep. As such, only trusted users should be allowed to set
variables in this manner.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters)
to be used in pathnames as well as command line arguments in the
sudoers file. Wildcard matching is done via the POSIX
fnmatch(3) routine. Note that these are not regular expressions.
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*
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Matches any set of zero or more characters.
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?
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Matches any single character.
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[...]
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Matches any character in the specified range.
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[!...]
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Matches any character not in the specified range.
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\x
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For any character x, evaluates to x. This is used to
escape special characters such as: *, ?, [, and }.
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Note that a forward slash (’/’) will not be matched by
wildcards used in the pathname. When matching the command
line arguments, however, a slash does get matched by
wildcards. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
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‘‘’’
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If the empty string "" is the only command line argument in the
sudoers entry it means that command is not allowed to be run
with any arguments.
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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 ALL is a built-in alias that always causes
a match to succeed. It can be used wherever one might otherwise
use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias.
You should not try to define your own alias called ALL as the
built-in alias will be used in preference to your own. Please note
that using ALL can be dangerous since in a command context, it
allows the user to run any command on the system.
An exclamation point (’!’) can be used as a logical not operator
both in an alias and in front of a Cmnd. This allows one to
exclude certain values. Note, however, that using a ! in
conjunction with the built-in ALL alias to allow a user to
run all but a few commands rarely works as intended (see SECURITY
NOTES below).
Long lines can be continued with a backslash (’\’) as the last
character on the line.
Whitespace between elements in a list as well as special syntactic
characters in a User Specification (’=’, ’:’, ’(’, ’)’) is optional.
The following characters must be escaped with a backslash (’\’) when
used as part of a word (e.g. a username or hostname):
’@’, ’!’, ’=’, ’:’, ’,’, ’(’, ’)’, ’\’.
SUDOERS OPTIONS
Sudo’s behavior can be modified by Default_Entry lines, as
explained earlier. A list of all supported Defaults parameters,
grouped by type, are listed below.
Flags:
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long_otp_prompt
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When validating with a One Time Password scheme (S/Key or OPIE),
a two-line prompt is used to make it easier to cut and paste the
challenge to a local window. It’s not as pretty as the default but
some people find it more convenient. This flag is off
by default.
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ignore_dot
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If set, sudo will ignore ’.’ or ’’ (current dir) in the PATH
environment variable; the PATH itself is not modified. This
flag is off by default. Currently, while it is possible
to set ignore_dot in sudoers, its value is not used. This option
should be considered read-only (it will be fixed in a future version
of sudo).
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mail_always
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Send mail to the mailto user every time a users runs sudo.
This flag is off by default.
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mail_badpass
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Send mail to the mailto user if the user running sudo does not
enter the correct password. This flag is off by default.
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mail_no_user
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If set, mail will be sent to the mailto user if the invoking
user is not in the sudoers file. This flag is on
by default.
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mail_no_host
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If set, mail will be sent to the mailto user if the invoking
user exists in the sudoers file, but is not allowed to run
commands on the current host. This flag is off by default.
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mail_no_perms
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If set, mail will be sent to the mailto user if the invoking
user is allowed to use sudo but the command they are trying is not
listed in their sudoers file entry or is explicitly denied.
This flag is off by default.
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tty_tickets
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If set, users must authenticate on a per-tty basis. Normally,
sudo uses a directory in the ticket dir with the same name as
the user running it. With this flag enabled, sudo will use a
file named for the tty the user is logged in on in that directory.
This flag is off by default.
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authenticate
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If set, users must authenticate themselves via a password (or other
means of authentication) before they may run commands. This default
may be overridden via the PASSWD and NOPASSWD tags.
This flag is on by default.
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root_sudo
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If set, root is allowed to run sudo too. Disabling this prevents users
from chaining sudo commands to get a root shell by doing something
like "sudo sudo /bin/sh". Note, however, that turning off root_sudo
will also prevent root and from running sudoedit.
Disabling root_sudo provides no real additional security; it
exists purely for historical reasons.
This flag is on by default.
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log_host
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If set, the hostname will be logged in the (non-syslog) sudo log file.
This flag is off by default.
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log_year
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If set, the four-digit year will be logged in the (non-syslog) sudo log file.
This flag is off by default.
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shell_noargs
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If set and sudo is invoked with no arguments it acts as if the
-s flag had been given. That is, it runs a shell as root (the
shell is determined by the SHELL environment variable if it is
set, falling back on the shell listed in the invoking user’s
/etc/passwd entry if not). This flag is off by default.
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set_home
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If set and sudo is invoked with the -s flag the HOME
environment variable will be set to the home directory of the target
user (which is root unless the -u option is used). This effectively
makes the -s flag imply -H. This flag is off by default.
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always_set_home
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If set, sudo will set the HOME environment variable to the home
directory of the target user (which is root unless the -u option is used).
This effectively means that the -H flag is always implied.
This flag is off by default.
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path_info
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Normally, sudo will tell the user when a command could not be
found in their PATH environment variable. Some sites may wish
to disable this as it could be used to gather information on the
location of executables that the normal user does not have access
to. The disadvantage is that if the executable is simply not in
the user’s PATH, sudo will tell the user that they are not
allowed to run it, which can be confusing. This flag is off by
default.
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preserve_groups
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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.
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fqdn
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Set this flag if you want to put fully qualified hostnames in the
sudoers file. I.e., instead of myhost you would use myhost.mydomain.edu.
You may still use the short form if you wish (and even mix the two).
Beware that turning on fqdn requires sudo to make DNS lookups
which may make sudo unusable if DNS stops working (for example
if the machine is not plugged into the network). Also note that
you must use the host’s official name as DNS knows it. That is,
you may not use a host alias (CNAME entry) due to performance
issues and the fact that there is no way to get all aliases from
DNS. If your machine’s hostname (as returned by the hostname
command) is already fully qualified you shouldn’t need to set
fqdn. This flag is off by default.
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insults
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If set, sudo will insult users when they enter an incorrect
password. This flag is off by default.
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requiretty
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If set, sudo will only run when the user is logged in to a real
tty. This will disallow things like "rsh somehost sudo ls" since
rsh(1) does not allocate a tty. Because it is not possible to turn
off echo when there is no tty present, some sites may wish to set
this flag to prevent a user from entering a visible password. This
flag is off by default.
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env_editor
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If set, visudo will use the value of the EDITOR or VISUAL
environment variables before falling back on the default editor list.
Note that this may create a security hole as it allows the user to
run any arbitrary command as root without logging. A safer alternative
is to place a colon-separated list of editors in the editor
variable. visudo will then only use the EDITOR or VISUAL if
they match a value specified in editor. This flag is off by
default.
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rootpw
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If set, sudo will prompt for the root password instead of the password
of the invoking user. This flag is off by default.
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runaspw
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If set, sudo will prompt for the password of the user defined by the
runas_default option (defaults to root) instead of the
password of the invoking user. This flag is off by default.
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targetpw
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If set, sudo will prompt for the password of the user specified by
the -u flag (defaults to root) instead of the password of the
invoking user. Note that this precludes the use of a uid not listed
in the passwd database as an argument to the -u flag.
This flag is off by default.
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set_logname
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Normally, sudo will set the LOGNAME, USER and USERNAME
environment variables to the name of the target user (usually root
unless the -u flag is given). However, since some programs
(including the RCS revision control system) use LOGNAME to
determine the real identity of the user, it may be desirable to
change this behavior. This can be done by negating the set_logname
option. Note that if the env_reset option has not been disabled,
entries in the env_keep list will override the value of
set_logname.
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stay_setuid
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Normally, when sudo executes a command the real and effective
UIDs are set to the target user (root by default). This option
changes that behavior such that the real UID is left as the invoking
user’s UID. In other words, this makes sudo act as a setuid
wrapper. This can be useful on systems that disable some potentially
dangerous functionality when a program is run setuid. This option
is only effective on systems with either the setreuid() or setresuid()
function.
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env_reset
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If set, sudo will reset the environment to only contain the
LOGNAME, SHELL, USER, USERNAME and the SUDO_* variables. Any
variables in the caller’s environment that match the env_keep
and env_check lists are then added. The default contents of the
env_keep and env_check lists are displayed when sudo is
run by root with the -V option. If sudo was compiled with
the SECURE_PATH option, its value will be used for the PATH
environment variable. This flag is on by default.
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use_loginclass
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If set, 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.
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noexec
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If set, all commands run via sudo will behave as if the NOEXEC
tag has been set, unless overridden by a EXEC tag. See the
description of NOEXEC and EXEC below as well as the PREVENTING SHELL ESCAPES section at the end of this manual. This flag is off by default.
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ignore_local_sudoers
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If set via LDAP, parsing of @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 @sysconfdir@/sudoers.
When this option is present, @sysconfdir@/sudoers does not even need to exist.
Since this option tells sudo how to behave when no specific LDAP entries
have been matched, this sudoOption is only meaningful for the cn=defaults
section. This flag is off by default.
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Integers:
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passwd_tries
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The number of tries a user gets to enter his/her password before
sudo logs the failure and exits. The default is 3.
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Integers that can be used in a boolean context:
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loglinelen
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Number of characters per line for the file log. This value is used
to decide when to wrap lines for nicer log files. This has no
effect on the syslog log file, only the file log. The default is
80 (use 0 or negate the option to disable word wrap).
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timestamp_timeout
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Number of minutes that can elapse before sudo will ask for a
passwd again. The default is 5. Set this to 0 to always
prompt for a password.
If set to a value less than 0 the user’s timestamp will never
expire. This can be used to allow users to create or delete their
own timestamps via sudo -v and sudo -k respectively.
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passwd_timeout
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Number of minutes before the sudo password prompt times out.
The default is 5, set this to 0 for no password timeout.
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umask
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Umask to use when running the command. Negate this option or set
it to 0777 to preserve the user’s umask. The default is 0022.
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setenv
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Allow the user to disable the env_reset option from the command
line. Additionally, environment variables set via the command line
are not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users should
be allowed to set variables in this manner.
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Strings:
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mailsub
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Subject of the mail sent to the mailto user. The escape %h
will expand to the hostname of the machine.
Default is *** SECURITY information for %h ***.
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badpass_message
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Message that is displayed if a user enters an incorrect password.
The default is Sorry, try again. unless insults are enabled.
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timestampdir
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The directory in which sudo stores its timestamp files.
The default is /var/run/sudo.
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timestampowner
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The owner of the timestamp directory and the timestamps stored therein.
The default is root.
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passprompt
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The default prompt to use when asking for a password; can be overridden
via the -p option or the SUDO_PROMPT environment variable.
The following percent (‘%’) escapes are supported:
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%u
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expanded to the invoking user’s login name
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%U
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expanded to the login name of the user the command will
be run as (defaults to root)
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%h
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expanded to the local hostname without the domain name
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%H
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expanded to the local hostname including the domain name
(on if the machine’s hostname is fully qualified or the fqdn
option is set)
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%%
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two consecutive % characters are collapsed into a single % character
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The default value is Password:.
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runas_default
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The default user to run commands as if the -u flag is not specified
on the command line. This defaults to root.
Note that if runas_default is set it must occur before
any Runas_Alias specifications.
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syslog_goodpri
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Syslog priority to use when user authenticates successfully.
Defaults to notice.
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syslog_badpri
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Syslog priority to use when user authenticates unsuccessfully.
Defaults to alert.
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editor
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A colon (’:’) separated list of editors allowed to be used with
visudo. visudo will choose the editor that matches the user’s
EDITOR environment variable if possible, or the first editor in the
list that exists and is executable. The default is the path to vi
on your system.
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noexec_file
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Path to a shared library containing dummy versions of the execv(),
execve() and fexecve() library functions that just return an error.
This is used to implement the noexec functionality on systems that
support LD_PRELOAD or its equivalent. Defaults to /usr/local/libexec/sudo_noexec.
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Strings that can be used in a boolean context:
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|
|
lecture
|
This option controls when a short lecture will be printed along with
the password prompt. It has the following possible values:
|
|
|
never
|
Never lecture the user.
|
|
once
|
Only lecture the user the first time they run sudo.
|
|
always
|
Always lecture the user.
|
|
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.
|
|
lecture_file
|
Path to a file containing an alternate sudo lecture that will
be used in place of the standard lecture if the named file exists.
|
|
logfile
|
Path to the sudo log file (not the syslog log file). Setting a path
turns on logging to a file; negating this option turns it off.
|
|
syslog
|
Syslog facility if syslog is being used for logging (negate to
disable syslog logging). Defaults to local2.
|
|
mailerpath
|
Path to mail program used to send warning mail.
Defaults to the path to sendmail found at configure time.
|
|
mailerflags
|
Flags to use when invoking mailer. Defaults to -t.
|
|
mailto
|
Address to send warning and error mail to. The address should
be enclosed in double quotes (") to protect against sudo
interpreting the @ sign. Defaults to root.
|
|
exempt_group
|
Users in this group are exempt from password and PATH requirements.
This is not set by default.
|
|
verifypw
|
This option controls when a password will be required when a user runs
sudo with the -v flag. It has the following possible values:
|
|
|
all
|
All the user’s sudoers entries for the current host must have
the NOPASSWD flag set to avoid entering a password.
|
|
any
|
At least one of the user’s sudoers entries for the current host
must have the NOPASSWD flag set to avoid entering a password.
|
|
never
|
The user need never enter a password to use the -v flag.
|
|
always
|
The user must always enter a password to use the -v flag.
|
|
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.
|
|
listpw
|
This option controls when a password will be required when a
user runs sudo with the -l flag. It has the following possible values:
|
|
|
all
|
All the user’s sudoers entries for the current host must have
the NOPASSWD flag set to avoid entering a password.
|
|
any
|
At least one of the user’s sudoers entries for the current host
must have the NOPASSWD flag set to avoid entering a password.
|
|
never
|
The user need never enter a password to use the -l flag.
|
|
always
|
The user must always enter a password to use the -l flag.
|
|
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.
|
|
Lists that can be used in a boolean context:
|
|
|
env_check
|
Environment variables to be removed from the user’s environment if
the variable’s value contains % or / characters. This can
be used to guard against printf-style format vulnerabilities in
poorly-written programs. The argument may be a double-quoted,
space-separated list or a single value without double-quotes. The
list can be replaced, added to, deleted from, or disabled by using
the =, +=, -=, and ! operators respectively. Regardless
of whether the env_reset option is enabled or disabled, variables
specified by env_check will be preserved in the environment if
they pass the aforementioned check. The default list of environment
variables to check is displayed when sudo is run by root with
the -V option.
|
|
env_delete
|
Environment variables to be removed from the user’s environment.
The argument may be a double-quoted, space-separated list or a
single value without double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =, +=, -=, and
! operators respectively. The default list of environment
variables to remove is displayed when sudo is run by root with the
-V option. Note that many operating systems will remove potentially
dangerous variables from the environment of any setuid process (such
as sudo).
|
|
env_keep
|
Environment variables to be preserved in the user’s environment
when the env_reset option is in effect. This allows fine-grained
control over the environment sudo-spawned processes will receive.
The argument may be a double-quoted, space-separated list or a
single value without double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the =, +=, -=, and
! operators respectively. The default list of variables to keep
is displayed when sudo is run by root with the -V option.
|
|
When logging via syslog(3), sudo accepts the following values
for the syslog facility (the value of the syslog Parameter):
authpriv (if your OS supports it), auth, daemon, user,
local0, local1, local2, local3, local4, local5,
local6, and local7. The following syslog priorities are
supported: alert, crit, debug, emerg, err, info,
notice, and warning.
FILES
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
EXAMPLES
Since the sudoers file is parsed in a single pass, order is
important. In general, you should structure sudoers such that
the Host_Alias, User_Alias, and Cmnd_Alias specifications
come first, followed by any Default_Entry lines, and finally the
Runas_Alias and user specifications. The basic rule of thumb
is you cannot reference an Alias that has not already been defined.
Below are example sudoers entries. Admittedly, some of
these are a bit contrived. First, we define our aliases:
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBMASTERS = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = master, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \
/usr/local/bin/tcsh, /usr/bin/rsh, \
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
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.
# Override built-in defaults
Defaults syslog=auth
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may
run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any
host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any
command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins (bostley, jwfox, and crawl) may run any
command on any host but they must authenticate themselves first
(since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias
(the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0).
Of those networks, only 128.138.204.0 has an explicit netmask (in
CIDR notation) indicating it is a class C network. For the other
networks in CSNETS, the local machine’s netmask will be used
during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias
(the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance.
Here, those are commands related to backups, killing processes, the
printing system, shutting down the system, and any commands in the
directory /usr/oper/bin/.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root
The user pete is allowed to change anyone’s password except for
root on the HPPA machines. Note that this assumes passwd(1)
does not take multiple usernames on the command line.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines
as any user listed in the OP Runas_Alias (root and operator).
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup.
Sudo knows that biglab is a netgroup due to the ’+’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers
as well as add and remove users, so they are allowed to run those
commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root
but he is not allowed to give su(1) any flags.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those
in the SERVERS Host_Alias (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run
any commands in the directory /usr/bin/ except for those commands
belonging to the SU and SHELLS Cmnd_Aliases.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/
but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to
kill hung processes.
WEBMASTERS www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBMASTERS User_Alias (will,
wendy, and wim), may run any command as user www (which owns the
web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias (orion, perseus, hercules) without entering a password.
This is a bit tedious for users to type, so it is a prime candidate
for encapsulating in a shell script.
SECURITY NOTES
It is generally not effective to subtract commands from ALL
using the ’!’ operator. A user can trivially circumvent this
by copying the desired command to a different name and then
executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn’t really prevent bill from running the commands listed in
SU or SHELLS since he can simply copy those commands to a
different name, or use a shell escape from an editor or other
program. Therefore, these kind of restrictions should be considered
advisory at best (and reinforced by policy).
PREVENTING SHELL ESCAPES
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 three basic approaches to this problem:
|
|
|
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 sudoedit is a better solution to
running editors via sudo. Due to the large number of programs that
offer shell escapes, restricting users to the set of programs that
do not if often unworkable.
|
|
noexec
|
Many systems that support shared libraries have the ability to
override default library functions by pointing an environment
variable (usually LD_PRELOAD) to an alternate shared library.
On such systems, sudo’s noexec functionality can be used to
prevent a program run by sudo from executing any other programs.
Note, however, that this applies only to native dynamically-linked
executables. Statically-linked executables and foreign executables
running under binary emulation are not affected.
To tell whether or not sudo supports noexec, you can run
the following as root:
sudo -V | grep "dummy exec"
If the resulting output contains a line that begins with:
File containing dummy exec functions:
then sudo may be able to replace the exec family of functions
in the standard library with its own that simply return an error.
Unfortunately, there is no foolproof way to know whether or not
noexec will work at compile-time. Noexec should work on
SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX
11.x. It is known not to work on AIX and UnixWare. Noexec
is expected to work on most operating systems that support the
LD_PRELOAD environment variable. Check your operating system’s
manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld,
dld.sl, rld, or loader) to see if LD_PRELOAD is supported.
To enable noexec for a command, use the NOEXEC tag as documented
in the User Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi
with noexec enabled. This will prevent those two commands from
executing other commands (such as a shell). If you are unsure
whether or not your system is capable of supporting noexec you
can always just try it out and see if it works.
|
|
Note that restricting shell escapes is not a panacea. Programs
running as root are still capable of many potentially hazardous
operations (such as changing or overwriting files) that could lead
to unintended privilege escalation. In the specific case of an
editor, a safer approach is to give the user permission to run
sudoedit.
SEE ALSO
rsh(1), su(1), fnmatch(3), sudo(8), visudo(8)
CAVEATS
The sudoers file should always be edited by the visudo
command which locks the file and does grammatical checking. It is
imperative that sudoers be free of syntax errors since sudo
will not run with a syntactically incorrect sudoers file.
When using netgroups of machines (as opposed to users), if you
store fully qualified hostnames in the netgroup (as is usually the
case), you either need to have the machine’s hostname be fully qualified
as returned by the hostname command or use the fqdn option in
sudoers.
BUGS
If you feel you have found a bug in sudo, please submit a bug report
at http://www.sudo.ws/sudo/bugs/
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.
DISCLAIMER
Sudo is provided ‘‘AS IS’’ and any express or implied warranties,
including, but not limited to, the implied warranties of merchantability
and fitness for a particular purpose are disclaimed. See the LICENSE
file distributed with sudo or http://www.sudo.ws/sudo/license.html
for complete details.
Top of page |
Section 5 |
| 1.6.9 | SUDOERS (5) | July 16, 2007 |
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