be more direct

[debian/sudo] / doc / sudo.pod

Copyright (c) 1994-1996, 1998-2005, 2007-2011
        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

sudo, sudoedit - execute a command as another user

=head1 SYNOPSIS

B<sudo> S<[B<-D> I<level>]> B<-h> | B<-K> | B<-k> | B<-V>

B<sudo> B<-v> [B<-AknS>]
S<[B<-a> I<auth_type>]>
S<[B<-D> I<level>]>
S<[B<-g> I<group name>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-u> I<user name>|I<#uid>]>

B<sudo> B<-l[l]> [B<-AknS>]
S<[B<-a> I<auth_type>]>
S<[B<-D> I<level>]>
S<[B<-g> I<group name>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-U> I<user name>]> S<[B<-u> I<user name>|I<#uid>]> [I<command>]

B<sudo> [B<-AbEHnPS>]
S<[B<-a> I<auth_type>]>
S<[B<-C> I<fd>]>
S<[B<-D> I<level>]>
S<[B<-c> I<class>|I<->]>
S<[B<-g> I<group name>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-r> I<role>]> S<[B<-t> I<type>]>
S<[B<-u> I<user name>|I<#uid>]>
S<[B<VAR>=I<value>]> S<[B<-i> | B<-s>]> [I<command>]

B<sudoedit> [B<-AnS>]
S<[B<-a> I<auth_type>]>
S<[B<-C> I<fd>]>
S<[B<-c> I<class>|I<->]>
S<[B<-D> I<level>]>
S<[B<-g> I<group name>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-u> I<user name>|I<#uid>]> file ...

=head1 DESCRIPTION

B<sudo> allows a permitted user to execute a I<command> as the
superuser or another user, as specified by the security policy.
The real and effective uid and gid are set to match those of the
target user, as specified in the password database, and the group
vector is initialized based on the group database (unless the B<-P>
option was specified).

B<sudo> supports a plugin architecture for security policies and
input/output logging.  Third parties can develop and distribute
their own policy and I/O logging modules to work seemlessly with
the B<sudo> front end.  The default security policy is I<sudoers>,
which is configured via the file F<@sysconfdir@/sudoers>, or via
LDAP.  See the L<PLUGINS> section for more information.

The security policy determines what privileges, if any, a user has
to run B<sudo>.  The policy may require that users authenticate
themselves with a password or another authentication mechanism.  If
authentication is required, B<sudo> will exit if the user's password
is not entered within a configurable time limit.  This limit is
policy-specific; the default password prompt timeout for the
I<sudoers> security policy is C<@password_timeout@> minutes.

Security policies may support credential caching to allow the user
to run B<sudo> again for a period of time without requiring
authentication.  The I<sudoers> policy caches credentials for
C<@timeout@> minutes, unless overridden in L<sudoers(5)>.  By
running B<sudo> with the B<-v> option, a user can update the cached
credentials without running a I<command>.

When invoked as B<sudoedit>, the B<-e> option (described below),
is implied.

Security policies may log successful and failed attempts to use
B<sudo>.  If an I/O plugin is configured, the running command's
input and output may be logged as well.

=head1 OPTIONS

B<sudo> accepts the following command line options:

=over 12

=item -A

Normally, if B<sudo> requires a password, it will read it from the
user's terminal.  If the B<-A> (I<askpass>) option is specified,
a (possibly graphical) helper program is executed to read the user's
password and output the password to the standard output.  If the
C<SUDO_ASKPASS> environment variable is set, it specifies the path
to the helper program.  Otherwise, if F<@sysconfdir@/sudo.conf>
contains a line specifying the askpass program, that value will be
used.  For example:

    # Path to askpass helper program
    Path askpass /usr/X11R6/bin/ssh-askpass

If no askpass program is available, sudo will exit with an error.

=item -a I<type>

The B<-a> (I<authentication type>) option causes B<sudo> to use the
specified authentication type when validating the user, as allowed
by F</etc/login.conf>.  The system administrator may specify a list
of sudo-specific authentication methods by adding an "auth-sudo"
entry in F</etc/login.conf>.  This option is only available on systems
that support BSD authentication.

=item -b

The B<-b> (I<background>) option tells B<sudo> to run the given
command in the background.  Note that if you use the B<-b>
option you cannot use shell job control to manipulate the process.
Most interactive commands will fail to work properly in background
mode.

=item -C I<fd>

Normally, B<sudo> will close all open file descriptors other than
standard input, standard output and standard error.  The B<-C>
(I<close from>) option allows the user to specify a starting point
above the standard error (file descriptor three).  Values less than
three are not permitted.  The security policy may restrict the
user's ability to use the B<-C> option.  The I<sudoers> policy only
permits use of the B<-C> option when the administrator has enabled
the I<closefrom_override> option.

=item -c I<class>

The B<-c> (I<class>) option causes B<sudo> to run the specified command
with resources limited by the specified login class.  The I<class>
argument can be either a class name as defined in F</etc/login.conf>,
or a single '-' character.  Specifying a I<class> of C<-> indicates
that the command should be run restricted by the default login
capabilities for the user the command is run as.  If the I<class>
argument specifies an existing user class, the command must be run
as root, or the B<sudo> command must be run from a shell that is already
root.  This option is only available on systems with BSD login classes.

=item -D I<level>

Enable debugging of B<sudo> plugins and B<sudo> itself.  The I<level>
may be a value from 1 through 9.

=item -E

The B<-E> (I<preserve> I<environment>) option indicates to the
security policy that the user wishes to preserve their existing
environment variables.  The security policy may return an error if
the B<-E> option is specified and the user does not have permission
to preserve the environment.

=item -e

The B<-e> (I<edit>) option indicates that, instead of running a
command, the user wishes to edit one or more files.  In lieu of a
command, the string "sudoedit" is used when consulting the security
policy.  If the user is authorized by the policy, the following
steps are taken:

=over 4

=item 1.

Temporary copies are made of the files to be edited with the owner
set to the invoking user.

=item 2.

The editor specified by the policy is run to edit the temporary files.
The I<sudoers> policy uses the C<SUDO_EDITOR>, C<VISUAL> and C<EDITOR>
environment variables (in that order).  If none of C<SUDO_EDITOR>,
C<VISUAL> or C<EDITOR> are set, the first program listed in the
I<editor> L<sudoers(5)> option is used.

=item 3.

If they have been modified, the temporary files are copied back to
their original location and the temporary versions are removed.

=back

If the specified file does not exist, it will be created.  Note
that unlike most commands run by B<sudo>, the editor is run with
the invoking user's environment unmodified.  If, for some reason,
B<sudo> is unable to update a file with its edited version, the
user will receive a warning and the edited copy will remain in a
temporary file.

=item -g I<group>

Normally, B<sudo> runs a command with the primary group set to the
one specified by the password database for the user the command is
being run as (by default, root).  The B<-g> (I<group>) option causes
B<sudo> to run the command with the primary group set to I<group>
instead.  To specify a I<gid> instead of a I<group name>, use
I<#gid>.  When running commands as a I<gid>, many shells require
that the '#' be escaped with a backslash ('\').  If no B<-u> option
is specified, the command will be run as the invoking user (not
root).  In either case, the primary group will be set to I<group>.

=item -H

The B<-H> (I<HOME>) option requests that the security policy set
the C<HOME> environment variable to the home directory of the target
user (root by default) as specified by the password database.
Depending on the policy, this may be the default behavior.

=item -h

The B<-h> (I<help>) option causes B<sudo> to print a short help message
to the standard output and exit.

=item -i [command]

The B<-i> (I<simulate initial login>) option runs the shell specified
by the password database entry of the target user as a login shell.
This means that login-specific resource files such as C<.profile>
or C<.login> will be read by the shell.  If a command is specified,
it is passed to the shell for execution via the shell's B<-c> option.
If no command is specified, an interactive shell is executed.
B<sudo> attempts to change to that user's home directory before
running the shell.  The security policy shall initialize the
environment to a minimal set of variables, similar to what is present
when a user logs in.  The I<Command Environment> section in the
L<sudoers(5)> manual documents how the B<-i> option affects the
environment in which a command is run when the I<sudoers> policy
is in use.

=item -K

The B<-K> (sure I<kill>) option is like B<-k> except that it removes
the user's cached credentials entirely and may not be used in
conjunction with a command or other option.  This option does not
require a password.  Not all security policies support credential
caching.

=item -k [command]

When used alone, the B<-k> (I<kill>) option to B<sudo> invalidates
the user's cached credentials.  The next time B<sudo> is run a
password will be required.  This option does not require a password
and was added to allow a user to revoke B<sudo> permissions from a
.logout file.  Not all security policies support credential
caching.

When used in conjunction with a command or an option that may require
a password, the B<-k> option will cause B<sudo> to ignore the user's
cached credentials.  As a result, B<sudo> will prompt for a password
(if one is required by the security policy) and will not update the
user's cached credentials.

=item -l[l] [I<command>]

If no I<command> is specified, the B<-l> (I<list>) option will list
the allowed (and forbidden) commands for the invoking user (or the
user specified by the B<-U> option) on the current host.  If a
I<command> is specified and is permitted by the security policy,
the fully-qualified path to the command is displayed along with any
command line arguments.  If I<command> is specified but not allowed,
B<sudo> will exit with a status value of 1.  If the B<-l> option
is specified with an B<l> argument (i.e. B<-ll>), or if B<-l> is
specified multiple times, a longer list format is used.

=item -n

The B<-n> (I<non-interactive>) option prevents B<sudo> from prompting
the user for a password.  If a password is required for the command
to run, B<sudo> will display an error messages and exit.

=item -P

The B<-P> (I<preserve> I<group vector>) option causes B<sudo> to
preserve the invoking user's group vector unaltered.  By default,
the I<sudoers> policy will initialize the group vector to the list
of groups the target user is in.  The real and effective group IDs,
however, are still set to match the target user.

=item -p I<prompt>

The B<-p> (I<prompt>) option allows you to override the default
password prompt and use a custom one.  The following percent (`C<%>')
escapes are supported by the I<sudoers> policy:

=over 4

=item C<%H>

expanded to the host name including the domain name (on if
the machine's host name is fully qualified or the I<fqdn> option
is set in L<sudoers(5)>)

=item C<%h>

expanded to the local host name without the domain name

=item C<%p>

expanded to the name of the user whose password is being requested
(respects the I<rootpw>, I<targetpw> and I<runaspw> flags in
L<sudoers(5)>)

=item C<%U>

expanded to the login name of the user the command will be run as
(defaults to root unless the C<-u> option is also specified)

=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 prompt specified by the B<-p> option will override the system
password prompt on systems that support PAM unless the
I<passprompt_override> flag is disabled in I<sudoers>.

=item -r I<role>

The B<-r> (I<role>) option causes the new (SELinux) security context to 
have the role specified by I<role>.

=item -S

The B<-S> (I<stdin>) option causes B<sudo> to read the password from
the standard input instead of the terminal device.  The password must
be followed by a newline character.

=item -s [command]

The B<-s> (I<shell>) option runs the shell specified by the I<SHELL>
environment variable if it is set or the shell as specified in the
password database.  If a command is specified, it is passed to the
shell for execution via the shell's B<-c> option.  If no command
is specified, an interactive shell is executed.

=item -t I<type>

The B<-t> (I<type>) option causes the new (SELinux) security context to 
have the type specified by I<type>.  If no type is specified, the default
type is derived from the specified role.

=item -U I<user>

The B<-U> (I<other user>) option is used in conjunction with the
B<-l> option to specify the user whose privileges should be listed.
The security policy may restrict listing other users' privileges.
The I<sudoers> policy only allows root or a user with the C<ALL>
privilege on the current host to use this option.

=item -u I<user>

The B<-u> (I<user>) option causes B<sudo> to run the specified
command as a user other than I<root>.  To specify a I<uid> instead
of a I<user name>, use I<#uid>.  When running commands as a I<uid>,
many shells require that the '#' be escaped with a backslash ('\').
Security policies may restrict I<uid>s to those listed in the
password database.  The I<sudoers> policy allows I<uid>s that are
not in the password database as long as the I<targetpw> option is
not set.  Other security policies may not support this.

=item -V

The B<-V> (I<version>) option causes B<sudo> to print its version
string and the version string of the security policy plugin and any
I/O plugins.  If the invoking user is already root the B<-V> option
will display the arguments passed to configure when I<sudo> was
built and plugins may display more verbose information such as
default options.

=item -v

When given the B<-v> (I<validate>) option, B<sudo> will update the
user's cached credentials, authenticating the user's password if
necessary.  For the I<sudoers> plugin, this extends the B<sudo>
timeout for another C<@timeout@> minutes (or whatever the timeout
is set to in I<sudoers>) but does not run a command.  Not all
security policies support cached credentials.

=item --

The B<--> option indicates that B<sudo> should stop processing command
line arguments.

=back

Environment variables to be set for the command may also be passed
on the command line in the form of B<VAR>=I<value>, e.g.
B<LD_LIBRARY_PATH>=I</usr/local/pkg/lib>.  Variables passed on the
command line are subject to the same restrictions as normal environment
variables with one important exception.  If the I<setenv> option
is set in I<sudoers>, the command to be run has the C<SETENV> tag
set or the command matched is C<ALL>, the user may set variables
that would overwise be forbidden.  See L<sudoers(5)> for more information.

=head1 PLUGINS

Plugins are dynamically loaded based on the contents of the
F<@sysconfdir@/sudo.conf> file.  If no F<@sysconfdir@/sudo.conf>
file is present, or it contains no C<Plugin> lines, B<sudo>
will use the traditional 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
 #   Path askpass /path/to/askpass
 #   Path noexec /path/to/noexec.so
 #
 # 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.
 #
 Plugin policy_plugin sudoers.so
 Plugin io_plugin sudoers.so 

A C<Plugin> line consists of the C<Plugin> keyword, followed by the
I<symbol_name> and the I<path> to the shared object containing the
plugin.  The I<symbol_name> is the name of the C<struct policy_plugin>
or C<struct io_plugin> in the plugin shared object.  The I<path>
may be fully qualified or relative.  If not fully qualified it is
relative to the F<@prefix@/libexec> directory.  Any additional
parameters after the I<path> are ignored.  Lines that don't begin
with C<Plugin> or C<Path> are silently ignored

For more information, see the L<sudo_plugin(8)> manual.

=head1 PATHS

A C<Path> line consists of the C<Path> keyword, followed by the
name of the path to set and its value.  E.g.

 Path noexec @noexec_file@
 Path askpass /usr/X11R6/bin/ssh-askpass

The following plugin-agnostic paths may be set in the
F<@sysconfdir@/sudo.conf> file.

=over 16

=item askpass

The fully qualified path to a helper program used to read the user's
password when no terminal is available.  This may be the case when
B<sudo> is executed from a graphical (as opposed to text-based)
application.  The program specified by I<askpass> should display
the argument passed to it as the prompt and write the user's password
to the standard output.  The value of I<askpass> may be overridden
by the C<SUDO_ASKPASS> environment variable.

=item noexec

The fully-qualified 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 I<noexec>
functionality on systems that support C<LD_PRELOAD> or its equivalent.
Defaults to F<@noexec_file@>.

=back

=head1 RETURN VALUES

Upon successful execution of a program, the exit status from B<sudo>
will simply be the exit status of the program that was executed.

Otherwise, B<sudo> exits with a value of 1 if there is a
configuration/permission problem or if B<sudo> cannot execute the
given command.  In the latter case the error string is printed to
the standard error.  If B<sudo> cannot L<stat(2)> one or more entries
in the user's C<PATH>, an error is printed on stderr.  (If the
directory does not exist or if it is not really a directory, the
entry is ignored and no error is printed.)  This should not happen
under normal circumstances.  The most common reason for L<stat(2)>
to return "permission denied" is if you are running an automounter
and one of the directories in your C<PATH> is on a machine that is
currently unreachable.

=head1 SECURITY NOTES

B<sudo> tries to be safe when executing external commands.

To prevent command spoofing, B<sudo> checks "." and "" (both denoting
current directory) last when searching for a command in the user's
PATH (if one or both are in the PATH).  Note, however, that the
actual C<PATH> environment variable is I<not> modified and is passed
unchanged to the program that B<sudo> executes.

Please note that B<sudo> will normally only log the command it
explicitly runs.  If a user runs a command such as C<sudo su> or
C<sudo sh>, subsequent commands run from that shell are not subject
to B<sudo>'s security policy.  The same is true for commands that
offer shell escapes (including most editors).  If I/O logging is
enabled, subsequent commands will have their input and/or output
logged, but there will not be traditional logs for those commands.
Because of this, care must be taken when giving users access to
commands via B<sudo> to verify that the command does not inadvertently
give the user an effective root shell.  For more information, please
see the C<PREVENTING SHELL ESCAPES> section in L<sudoers(5)>.

=head1 ENVIRONMENT

B<sudo> utilizes the following environment variables.  The security
policy has control over the content of the command's environment.

=over 16

=item C<EDITOR>

Default editor to use in B<-e> (sudoedit) mode if neither C<SUDO_EDITOR>
nor C<VISUAL> is set

=item C<MAIL>

In B<-i> mode or when I<env_reset> is enabled in I<sudoers>, set
to the mail spool of the target user

=item C<HOME>

Set to the home directory of the target user if B<-i> or B<-H> are
specified, I<env_reset> or I<always_set_home> are set in I<sudoers>,
or when the B<-s> option is specified and I<set_home> is set in
I<sudoers>

=item C<PATH>

May be overridden by the security policy.

=item C<SHELL>

Used to determine shell to run with C<-s> option

=item C<SUDO_ASKPASS>

Specifies the path to a helper program used to read the password
if no terminal is available or if the C<-A> option is specified.

=item C<SUDO_COMMAND>

Set to the command run by sudo

=item C<SUDO_EDITOR>

Default editor to use in B<-e> (sudoedit) mode

=item C<SUDO_GID>

Set to the group ID of the user who invoked sudo

=item C<SUDO_PROMPT>

Used as the default password prompt

=item C<SUDO_PS1>

If set, C<PS1> will be set to its value for the program being run

=item C<SUDO_UID>

Set to the user ID of the user who invoked sudo

=item C<SUDO_USER>

Set to the login of the user who invoked sudo

=item C<USER>

Set to the target user (root unless the B<-u> option is specified)

=item C<VISUAL>

Default editor to use in B<-e> (sudoedit) mode if C<SUDO_EDITOR>
is not set

=back

=head1 FILES

=over 24

=item F<@sysconfdir@/sudo.conf>

B<sudo> plugin and path configuration

=back

=head1 EXAMPLES

Note: the following examples assume a properly configured security policy.

To get a file listing of an unreadable directory:

 $ sudo ls /usr/local/protected

To list the home directory of user yaz on a machine where the
file system holding ~yaz is not exported as root:

 $ sudo -u yaz ls ~yaz

To edit the F<index.html> file as user www:

 $ sudo -u www vi ~www/htdocs/index.html

To view system logs only accessible to root and users in the adm group:

 $ sudo -g adm view /var/log/syslog

To run an editor as jim with a different primary group:

 $ sudo -u jim -g audio vi ~jim/sound.txt

To shutdown a machine:

 $ sudo shutdown -r +15 "quick reboot"

To make a usage listing of the directories in the /home
partition.  Note that this runs the commands in a sub-shell
to make the C<cd> and file redirection work.

 $ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

=head1 SEE ALSO

L<grep(1)>, L<su(1)>, L<stat(2)>,
L<login_cap(3)>,
L<passwd(5)>, L<sudoers(5)>, L<sudo_plugin(8)>, L<sudoreplay(8)>, L<visudo(8)>

=head1 AUTHORS

Many people have worked on B<sudo> over the years; this
version consists of code written primarily by:

        Todd C. Miller

See the HISTORY file in the B<sudo> distribution or visit
http://www.sudo.ws/sudo/history.html for a short history
of B<sudo>.

=head1 CAVEATS

There is no easy way to prevent a user from gaining a root shell
if that user is allowed to run arbitrary commands via B<sudo>.
Also, many programs (such as editors) allow the user to run commands
via shell escapes, thus avoiding B<sudo>'s checks.  However, on
most systems it is possible to prevent shell escapes with the
L<sudoers(5)> module's I<noexec> functionality.

It is not meaningful to run the C<cd> command directly via sudo, e.g.,

 $ sudo cd /usr/local/protected

since when the command exits the parent process (your shell) will
still be the same.  Please see the EXAMPLES section for more information.

Running shell scripts via B<sudo> can expose the same kernel bugs that
make setuid shell scripts unsafe on some operating systems (if your OS
has a /dev/fd/ directory, setuid shell scripts are generally safe).

=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.