path: root/man/su.1.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
   SPDX-FileCopyrightText: 1989 - 1990, Julianne Frances Haugh
   SPDX-FileCopyrightText: 2007 - 2008, Nicolas François
   SPDX-License-Identifier: BSD-3-Clause
-->
<!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'>
          <replaceable>-</replaceable>
      </arg>
      <arg choice='opt'>
          <replaceable>username</replaceable>
          <arg choice='opt'>
              <replaceable>args</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
      <option>-</option> option may be used to provide an environment similar
      to what the user would expect had the user logged in directly. The
      <option>-c</option> option may be used to treat the next argument as a
      command by most shells.
    </para>

    <para>
      Options are recognized everywhere in the argument list. You can use the
      <option>--</option> argument to stop option parsing. The
      <option>-</option> option is special: it is also recognized after
      <option>--</option>, but has to be placed before
      <option>username</option>.
    </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>&nbsp;<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 interactive 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 before any
	    <option>username</option>.  For portability it is recommended
	    to use it as last option, before any
	    <option>username</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>&nbsp;<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 ordered list, 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;
      &ENV_HZ;
      &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>