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[debian/sudo] / sudo.pod

Copyright (c) 1994-1996, 1998-2005, 2007-2008
        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.

$Sudo: sudo.pod,v 1.120 2008/11/15 18:34:01 millert Exp $
=pod

=head1 NAME

sudo, sudoedit - execute a command as another user

=head1 SYNOPSIS

B<sudo> [B<-n>] B<-h> | B<-K> | B<-k> | B<-L> | B<-V> | B<-v>

B<sudo> B<-l[l]> [B<-AnS>] S<[B<-g> I<groupname>|I<#gid>]> S<[B<-U> I<username>]>
S<[B<-u> I<username>|I<#uid>]> [I<command>]

B<sudo> [B<-AbEHnPS>]
S<[B<-a> I<auth_type>]>
S<[B<-C> I<fd>]>
S<[B<-c> I<class>|I<->]>
S<[B<-g> I<groupname>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-r> I<role>]> S<[B<-t> I<type>]>
S<[B<-u> I<username>|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<-g> I<groupname>|I<#gid>]> S<[B<-p> I<prompt>]>
S<[B<-u> I<username>|I<#uid>]> file ...

=head1 DESCRIPTION

B<sudo> allows a permitted user to execute a I<command> as the
superuser or another user, as specified in the I<sudoers> file.
The real and effective uid and gid are set to match those of the
target user as specified in the passwd file and the group vector
is initialized based on the group file (unless the B<-P> option was
specified).  If the invoking user is root or if the target user is
the same as the invoking user, no password is required.  Otherwise,
B<sudo> requires that users authenticate themselves with a password
by default (NOTE: in the default configuration this is the user's
password, not the root password).  Once a user has been authenticated,
a timestamp is updated and the user may then use sudo without a
password for a short period of time (C<@timeout@> minutes unless
overridden in I<sudoers>).

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

B<sudo> determines who is an authorized user by consulting the file
F<@sysconfdir@/sudoers>.  By running B<sudo> with the B<-v> option,
a user can update the time stamp without running a I<command>. The
password prompt itself will also time out if the user's password
is not entered within C<@password_timeout@> minutes (unless overridden
via I<sudoers>).

If a user who is not listed in the I<sudoers> file tries to run a
command via B<sudo>, mail is sent to the proper authorities, as
defined at configure time or in the I<sudoers> file (defaults to
C<@mailto@>).  Note that the mail will not be sent if an unauthorized
user tries to run 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, B<sudo> 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 being run via a sudo-run script or
program.  Note however, that the sudoers lookup is still done for
root, not the user specified by C<SUDO_USER>.

B<sudo> can log both successful and unsuccessful attempts (as well
as errors) to syslog(3), a log file, or both.  By default B<sudo>
will log via syslog(3) but this is changeable at configure time
or via the I<sudoers> file.

=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
current terminal.  If the B<-A> (I<askpass>) option is specified,
a 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, the value specified by the I<askpass> option
in L<sudoers(5)> is used.

=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.

=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.  This option is only available if the
administrator has enabled the I<closefrom_override> option in
L<sudoers(5)>.

=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 -E

The B<-E> (I<preserve> I<environment>) option will override the
I<env_reset> option in L<sudoers(5)>).  It is only
available when either the matching command has the C<SETENV> tag
or the I<setenv> option is set in L<sudoers(5)>.

=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 I<sudoers> file.  If the user is authorized by I<sudoers>
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 C<SUDO_EDITOR>, C<VISUAL> or C<EDITOR>
environment variables is run to edit the temporary files.  If none
of C<SUDO_EDITOR>, C<VISUAL> or C<EDITOR> are set, the first program
listed in the I<editor> I<sudoers> variable 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> sets the primary group to the one specified by
the passwd 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 specified command with the primary group set to I<group>.  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 sets the C<HOME> environment variable
to the homedir of the target user (root by default) as specified
in passwd(5).  By default, B<sudo> does not modify C<HOME>
(see I<set_home> and I<always_set_home> in L<sudoers(5)>).

=item -h

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

=item -i [command]

The B<-i> (I<simulate initial login>) option runs the shell specified
in the L<passwd(5)> 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.  Otherwise, an interactive
shell is executed.  B<sudo> attempts to change to that user's home
directory before running the shell.  It also initializes the
environment, leaving I<DISPLAY> and I<TERM> unchanged, setting
I<HOME>, I<SHELL>, I<USER>, I<LOGNAME>, and I<PATH>, as well as
the contents of F</etc/environment> on Linux and AIX systems.
All other environment variables are removed.

=item -K

The B<-K> (sure I<kill>) option is like B<-k> except that it removes
the user's timestamp entirely.  Like B<-k>, this option does not
require a password.

=item -k

The B<-k> (I<kill>) option to B<sudo> invalidates the user's timestamp
by setting the time on it to the Epoch.  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.

=item -L

The B<-L> (I<list> defaults) option will list out the parameters
that may be set in a I<Defaults> line along with a short description
for each.  This option is useful in conjunction with L<grep(1)>.

=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 I<sudoers>, 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,
B<sudo> 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:

=over 4

=item C<%H>

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

=item C<%h>

expanded to the local hostname 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 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.

=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
L<passwd(5)>.  If a command is specified, it is passed to the shell
for execution.  Otherwise, 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.  Only
root or a user with B<sudo> C<ALL> on the current host may 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 ('\').
Note that if the I<targetpw> Defaults option is set (see L<sudoers(5)>)
it is not possible to run commands with a uid not listed in the
password database.

=item -V

The B<-V> (I<version>) option causes B<sudo> to print the version
number and exit.  If the invoking user is already root the B<-V>
option will print out a list of the defaults B<sudo> was compiled
with as well as the machine's local network addresses.

=item -v

If given the B<-v> (I<validate>) option, B<sudo> will update the
user's timestamp, prompting for the user's password if necessary.
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.

=item --

The B<--> option indicates that B<sudo> should stop processing command
line arguments.  It is most useful in conjunction with the B<-s> option.

=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 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> quits with an exit 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
stderr.  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.

There are two distinct ways to deal with environment variables.
By default, the I<env_reset> I<sudoers> option is enabled.
This causes commands to be executed with a minimal environment
containing C<TERM>, C<PATH>, C<HOME>, C<SHELL>, C<LOGNAME>, C<USER>
and C<USERNAME> in addition to variables from the invoking process
permitted by the I<env_check> and I<env_keep> I<sudoers> options.
There is effectively a whitelist for environment variables.

If, however, the I<env_reset> option is disabled in I<sudoers>, 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.

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
C<PATH> environment variable is further modified in Debian because of
the use of the I<SECURE_PATH> build option.

B<sudo> will check the ownership of its timestamp 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 timestamp directory is located in a directory
writable by anyone (e.g., F</tmp>), it is possible for a user to
create the timestamp directory before B<sudo> is run.  However,
because B<sudo> 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 timestamp dir.  This is unlikely to happen
since once the timestamp dir is owned by root and inaccessible by
any other user, the user placing files there would be unable to get
them back out.  To get around this issue you can use a directory
that is not world-writable for the timestamps (F</var/adm/sudo> for
instance) or create F<@timedir@> with the appropriate owner (root)
and permissions (0700) in the system startup files.

B<sudo> will not honor timestamps set far in the future.
Timestamps 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 timestamp with a bogus
date on systems that allow users to give away files.

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 will I<not> be
logged, nor will B<sudo>'s access control affect them.  The same
is true for commands that offer shell escapes (including most
editors).  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:

=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<HOME>

In B<-s> or B<-H> mode (or if sudo was configured with the
--enable-shell-sets-home option), set to homedir of the target user

=item C<PATH>

Set to a sane value if the I<secure_path> sudoers option is set.

=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@/sudoers>

List of who can run what

=item F<@timedir@>

Directory containing timestamps

=item F</etc/environment>

Initial environment for B<-i> mode on Linux and AIX

=back

=head1 EXAMPLES

Note: the following examples assume suitable L<sudoers(5)> entries.

To get a file listing of an unreadable directory:

 $ sudo ls /usr/local/protected

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

 $ sudo -u yazza ls ~yazza

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

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

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<visudo(8)>

The file /usr/share/doc/sudo/OPTIONS describes the options used for building
the Debian version of sudo, some of which change default behaviors documented
elsewhere in this document.

=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 B<sudo>'s
I<noexec> functionality.  See the L<sudoers(5)> manual
for details.

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.

If users have sudo C<ALL> there is nothing to prevent them from
creating their own program that gives them a root shell regardless
of any '!' elements in the user specification.

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.