<?xml version="1.0" encoding="UTF-8"?>
<!--
   Copyright (c) 1989 - 1990, Julianne Frances Haugh
   Copyright (c) 2007 - 2008, Nicolas François
   All rights reserved.
  
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:
   1. Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
   2. Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
   3. The name of the copyright holders or contributors may not be used to
      endorse or promote products derived from this software without
      specific prior written permission.
  
   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   ``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.  IN NO EVENT SHALL THE COPYRIGHT
   HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY CONSOLE               SYSTEM "login.defs.d/CONSOLE.xml">
<!ENTITY CONSOLE_GROUPS        SYSTEM "login.defs.d/CONSOLE_GROUPS.xml">
<!ENTITY DEFAULT_HOME          SYSTEM "login.defs.d/DEFAULT_HOME.xml">
<!ENTITY ENV_HZ                SYSTEM "login.defs.d/ENV_HZ.xml">
<!ENTITY ENVIRON_FILE          SYSTEM "login.defs.d/ENVIRON_FILE.xml">
<!ENTITY ENV_PATH              SYSTEM "login.defs.d/ENV_PATH.xml">
<!ENTITY ENV_SUPATH            SYSTEM "login.defs.d/ENV_SUPATH.xml">
<!ENTITY ENV_TZ                SYSTEM "login.defs.d/ENV_TZ.xml">
<!ENTITY LOGIN_STRING          SYSTEM "login.defs.d/LOGIN_STRING.xml">
<!ENTITY MAIL_CHECK_ENAB       SYSTEM "login.defs.d/MAIL_CHECK_ENAB.xml">
<!ENTITY MAIL_DIR              SYSTEM "login.defs.d/MAIL_DIR.xml">
<!ENTITY QUOTAS_ENAB           SYSTEM "login.defs.d/QUOTAS_ENAB.xml">
<!ENTITY SULOG_FILE            SYSTEM "login.defs.d/SULOG_FILE.xml">
<!ENTITY SU_NAME               SYSTEM "login.defs.d/SU_NAME.xml">
<!ENTITY SU_WHEEL_ONLY         SYSTEM "login.defs.d/SU_WHEEL_ONLY.xml">
<!ENTITY SYSLOG_SU_ENAB        SYSTEM "login.defs.d/SYSLOG_SU_ENAB.xml">
<!ENTITY USERGROUPS_ENAB       SYSTEM "login.defs.d/USERGROUPS_ENAB.xml">
<!-- SHADOW-CONFIG-HERE -->
]>
<refentry id='su.1'>
  <!--  $Id$ -->
  <refentryinfo>
    <author>
      <firstname>Julianne Frances</firstname>
      <surname>Haugh</surname>
      <contrib>Creation, 1989</contrib>
    </author>
    <author>
      <firstname>Thomas</firstname>
      <surname>Kłoczko</surname>
      <email>kloczek@pld.org.pl</email>
      <contrib>shadow-utils maintainer, 2000 - 2007</contrib>
    </author>
    <author>
      <firstname>Nicolas</firstname>
      <surname>François</surname>
      <email>nicolas.francois@centraliens.net</email>
      <contrib>shadow-utils maintainer, 2007 - now</contrib>
    </author>
  </refentryinfo>
  <refmeta>
    <refentrytitle>su</refentrytitle>
    <manvolnum>1</manvolnum>
    <refmiscinfo class="sectdesc">User Commands</refmiscinfo>
    <refmiscinfo class="source">shadow-utils</refmiscinfo>
    <refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
  </refmeta>
  <refnamediv id='name'>
    <refname>su</refname>
    <refpurpose>change user ID or become superuser</refpurpose>
  </refnamediv>
  <refsynopsisdiv id='synopsis'>
    <cmdsynopsis>
      <command>su</command>
      <arg choice='opt'>
	<replaceable>options</replaceable>
      </arg>
      <arg choice='opt'>
	<arg choice='plain'>
	  <replaceable>username</replaceable>
	</arg>
      </arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1 id='description'>
    <title>DESCRIPTION</title>
    <para>
      The <command>su</command> command is used to become another user during
      a login session. Invoked without a <option>username</option>, 
      <command>su</command> defaults to
      becoming the superuser. The optional argument <option>-</option> may
      be used to provide an environment similar to what the user would
      expect had the user logged in directly.
    </para>

    <para>
      Additional arguments may be provided after the username, in which case
      they are supplied to the user's login shell. In particular, an
      argument of <option>-c</option> will cause the next argument to be
      treated as a command by most command interpreters. The command will be
      executed by the shell specified in <filename>/etc/passwd</filename>
      for the target user.
    </para>

    <para>
      You can use the <option>--</option> argument to separate
      <command>su</command> options from the arguments supplied to the shell.
    </para>

    <para>The user will be prompted for a password, if appropriate. Invalid
      passwords will produce an error message. All attempts, both valid and
      invalid, are logged to detect abuse of the system.
    </para>

    <para>
      The current environment is passed to the new shell. The value of
      <envar>$PATH</envar> is reset to <filename>/bin:/usr/bin</filename>
      for normal users, or <filename>/sbin:/bin:/usr/sbin:/usr/bin</filename>
      for the superuser. This may be changed with the
      <option>ENV_PATH</option> and <option>ENV_SUPATH</option>
      definitions in <filename>/etc/login.defs</filename>.
    </para>

    <para>
      A subsystem login is indicated by the presence of a "*" as the first
      character of the login shell. The given home directory will be used as
      the root of a new file system which the user is actually logged into.
    </para>
  </refsect1>

  <refsect1 id='options'>
    <title>OPTIONS</title>
    <para>The options which apply to the <command>su</command> command are:
    </para>
    <variablelist remap='IP'>
      <varlistentry>
	<term>
	  <option>-c</option>, <option>--command</option>
	  <replaceable>COMMAND</replaceable>
	</term>
	<listitem>
	  <para>
	    Specify a command that will be invoked by the shell using its
	    <option>-c</option>.
	  </para>
	  <para>
	    The executed command will have no controlling terminal. This
	    option cannot be used to execute interractive programs which
	    need a controlling TTY.
	    <!-- This avoids TTY hijacking when su is used to lower
	         privileges -->
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-</option>, <option>-l</option>, <option>--login</option>
	</term>
	<listitem>
	  <para>
	    Provide an environment similar to what the user would expect had
	    the user logged in directly.
	  </para>
	  <para>
	    When <option>-</option> is used, it must be specified as the last
	    <command>su</command> option.
	    The other forms (<option>-l</option> and <option>--login</option>)
	    do not have this restriction.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-s</option>, <option>--shell</option>
	  <replaceable>SHELL</replaceable>
	</term>
	<listitem>
	  <para>The shell that will be invoked.</para>
	  <para>
	    The invoked shell is chosen from (highest priority first):
	    <!--This should be an orderedlist, but lists inside another
	        list does not work well with current docbook.
	        - nekral - 2009.06.03 -->
	    <variablelist>
	      <varlistentry><term></term><listitem>
		<para>The shell specified with --shell.</para>
	      </listitem></varlistentry>
	      <varlistentry><term></term><listitem>
		<para>
		  If <option>--preserve-environment</option> is used, the
		  shell specified by the <envar>$SHELL</envar> environment
		  variable.
		</para>
	      </listitem></varlistentry>
	      <varlistentry><term></term><listitem>
		<para>
		  The shell indicated in the <filename>/etc/passwd</filename>
		  entry for the target user.
		</para>
	      </listitem></varlistentry>
	      <varlistentry><term></term><listitem>
		<para><filename>/bin/sh</filename> if a shell could not be
		found by any above method.</para>
	      </listitem></varlistentry>
	    </variablelist>
	  </para>
	  <para>
	    If the target user has a restricted shell (i.e. the shell field of
	    this user's entry in <filename>/etc/passwd</filename> is not
	    listed in <filename>/etc/shells</filename>), then the
	    <option>--shell</option> option or the <envar>$SHELL</envar>
	    environment variable won't be taken into account, unless
	    <command>su</command> is called by root.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <option>-m</option>, <option>-p</option>,
	  <option>--preserve-environment</option>
	</term>
	<listitem>
	  <para>
	    Preserve the current environment, except for:
	    <variablelist>
	      <varlistentry>
		<term><envar>$PATH</envar></term>
		<listitem>
		  <para>
		    reset according to the
		    <filename>/etc/login.defs</filename> options
		    <option>ENV_PATH</option> or
		    <option>ENV_SUPATH</option> (see below);
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><envar>$IFS</envar></term>
		<listitem>
		  <para>
		    reset to
		    <quote>&lt;space&gt;&lt;tab&gt;&lt;newline&gt;</quote>,
		    if it was set.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </para>
	  <para>
	    If the target user has a restricted shell, this option has no
	    effect (unless <command>su</command> is called by root).
	  </para>
	  <para>
	    Note that the default behavior for the environment is the
	    following:
	    <variablelist>
	      <varlistentry><term></term><listitem>
		  <para>
		    The <envar>$HOME</envar>, <envar>$SHELL</envar>,
		    <envar>$USER</envar>, <envar>$LOGNAME</envar>,
		    <envar>$PATH</envar>, and <envar>$IFS</envar>
		    environment variables are reset.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry><term></term><listitem>
		  <para>
		    If <option>--login</option> is not used, the
		    environment is copied, except for the variables above.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry><term></term><listitem>
		  <para>
		    If <option>--login</option> is used, the
		    <envar>$TERM</envar>, <envar>$COLORTERM</envar>,
		    <envar>$DISPLAY</envar>, and
		    <envar>$XAUTHORITY</envar> environment variables are
		    copied if they were set.
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry condition="no_pam"><term></term><listitem>
		  <para>
		    If <option>--login</option> is used, the
		    <envar>$TZ</envar>, <envar>$HZ</envar>, and
		    <envar>$MAIL</envar> environment
		    variables are set according to the 
		    <filename>/etc/login.defs</filename>
		    options <option>ENV_TZ</option>,
		    <option>ENV_HZ</option>, <option>MAIL_DIR</option>, and
		    <option>MAIL_FILE</option> (see below).
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry condition="no_pam"><term></term><listitem>
		  <para>
		    If <option>--login</option> is used, other environment
		    variables might be set by the
		    <option>ENVIRON_FILE</option> file (see below).
		  </para>
		</listitem>
	      </varlistentry>
	      <varlistentry condition="pam"><term></term><listitem>
		  <para>
		    Other environments might be set by PAM modules.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='caveats'>
    <title>CAVEATS</title>
    <para>
      This version of <command>su</command> has many compilation options,
      only some of which may be in use at any particular site.
    </para>
  </refsect1>

  <refsect1 id='configuration'>
    <title>CONFIGURATION</title>
    <para>
      The following configuration variables in
      <filename>/etc/login.defs</filename> change the behavior of this
      tool:
    </para>
    <variablelist>
      &CONSOLE;
      &CONSOLE_GROUPS;
      &DEFAULT_HOME;
      <phrase condition="no_pam">&ENV_HZ;</phrase>
      &ENVIRON_FILE;
      &ENV_PATH;
      &ENV_SUPATH;
      &ENV_TZ;
      <phrase condition="no_pam">&LOGIN_STRING;</phrase>
      &MAIL_CHECK_ENAB;
      <phrase condition="no_pam">&MAIL_DIR;</phrase>
      &QUOTAS_ENAB;
      &SULOG_FILE;
      &SU_NAME;
      &SU_WHEEL_ONLY;
      &SYSLOG_SU_ENAB;
      <phrase condition="no_pam">&USERGROUPS_ENAB;</phrase>
    </variablelist>
  </refsect1>

  <refsect1 id='files'>
    <title>FILES</title>
    <variablelist>
      <varlistentry>
	<term><filename>/etc/passwd</filename></term>
	<listitem>
	  <para>User account information.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><filename>/etc/shadow</filename></term>
	<listitem>
	  <para>Secure user account information.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><filename>/etc/login.defs</filename></term>
	<listitem>
	  <para>Shadow password suite configuration.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1 id='exit_values'>
    <title>EXIT VALUES</title>
    <para>
      On success, <command>su</command> returns the exit value of the
      command it executed.
    </para>
    <para>
      If this command was terminated by a signal, <command>su</command>
      returns the number of this signal plus 128.
    </para>
    <para>
      If su has to kill the command (because it was asked to terminate,
      and the command did not terminate in time), <command>su</command>
      returns 255.
    </para>
    <para>
      Some exit values from <command>su</command> are independent from the
      executed command:
      <variablelist>
	<varlistentry>
	  <term><replaceable>0</replaceable></term>
	  <listitem>
	    <para>success (<option>--help</option> only)</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>1</replaceable></term>
	  <listitem>
	    <para>System or authentication failure</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>126</replaceable></term>
	  <listitem>
	    <para>The requested command was not found</para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><replaceable>127</replaceable></term>
	  <listitem>
	    <para>The requested command could not be executed</para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </para>
  </refsect1>

  <refsect1 id='see_also'>
    <title>SEE ALSO</title>
    <para><citerefentry>
	<refentrytitle>login</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>sg</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>,
      <citerefentry>
	<refentrytitle>sh</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>.
    </para>
  </refsect1>
</refentry>
