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PostgreSQL documentation
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<refentry id="APP-POSTGRES">
 <refmeta>
  <refentrytitle id="APP-POSTGRES-TITLE"><application>postgres</application></refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>postgres</refname>
  <refpurpose>run a <productname>PostgreSQL</productname> server in single-user mode</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <!-- standalone call -->
   <command>postgres</command>
   <arg>-A <group choice="plain"><arg>0</arg><arg>1</arg></group></arg>
   <arg>-B <replaceable>nbuffers</replaceable></arg>
   <arg>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></arg>
   <arg>-d <replaceable>debug-level</replaceable></arg>
   <arg>-D <replaceable>datadir</replaceable></arg>
   <arg>-e</arg>
   <arg>-E</arg>
   <arg>-f<group choice="plain"><arg>s</arg><arg>i</arg><arg>t</arg><arg>n</arg><arg>m</arg><arg>h</arg></group></arg>
   <arg>-F</arg>
   <arg>-i</arg>
   <arg>-N</arg>
   <arg>-o <replaceable>filename</replaceable></arg>
   <arg>-O</arg>
   <arg>-P</arg>
   <group>
    <arg>-s</arg>
    <arg>-t<group choice="plain"><arg>pa</arg><arg>pl</arg><arg>ex</arg></group></arg>
   </group>
   <arg>-S <replaceable>sort-mem</replaceable></arg>
   <arg>-W <replaceable>seconds</replaceable></arg>
   <arg>--<replaceable>name</replaceable>=<replaceable>value</replaceable></arg>
   <arg choice="plain"><replaceable>database</replaceable></arg>
   <sbr>
   <!-- postmaster fork -->
   <command>postgres</command>
   <arg>-A <group choice="plain"><arg>0</arg><arg>1</arg></group></arg>
   <arg>-B <replaceable>nbuffers</replaceable></arg>
   <arg>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></arg>
   <arg>-d <replaceable>debug-level</replaceable></arg>
   <arg>-D <replaceable>datadir</replaceable></arg>
   <arg>-e</arg>
   <arg>-f<group choice="plain"><arg>s</arg><arg>i</arg><arg>t</arg><arg>n</arg><arg>m</arg><arg>h</arg></group></arg>
   <arg>-F</arg>
   <arg>-i</arg>
   <arg>-o <replaceable>filename</replaceable></arg>
   <arg>-O</arg>
   <arg>-p <replaceable>database</replaceable></arg>
   <arg>-P</arg>
   <group>
    <arg>-s</arg>
    <arg>-t<group choice="plain"><arg>pa</arg><arg>pl</arg><arg>ex</arg></group></arg>
   </group>
   <arg>-S <replaceable>sort-mem</replaceable></arg>
   <arg>-v <replaceable>protocol-version</replaceable></arg>
   <arg>-W <replaceable>seconds</replaceable></arg>
   <arg>--<replaceable>name</replaceable>=<replaceable>value</replaceable></arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   The <filename>postgres</filename> executable is the actual
   <productname>PostgreSQL</productname> server process that processes
   queries.  It is normally not called directly; instead a <xref
   linkend="app-postmaster"> multiuser server is started.
  </para>

  <para>
   The second form above is how
   <application>postgres</application> is invoked by the <xref
   linkend="app-postmaster"> (only
   conceptually, since both <filename>postmaster</filename> and
   <filename>postgres</filename> are in fact the same program); it
   should not be invoked directly this way.  The first form invokes
   the server directly in interactive single-user mode.  The primary use
   for this mode is during bootstrapping by <xref linkend="app-initdb">.
   Sometimes it is used for debugging or disaster recovery.
  </para>

  <para>
   When invoked in interactive mode from the shell, the user can enter
   queries and the results will be printed to the screen, but in a
   form that is more useful for developers than end users.  But note
   that running a single-user backend is not truly suitable for
   debugging the server since no realistic interprocess communication
   and locking will happen.
  </para>

  <para>
   When running a stand-alone backend, the session user will be set to
   the user with ID 1.  This user does not actually have to exist, so
   a stand-alone backend can be used to manually recover from certain
   kinds of accidental damage to the system catalogs.  Implicit
   superuser powers are granted to the user with ID 1 in stand-alone
   mode.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    When <application>postgres</application> is started by a <xref
    linkend="app-postmaster"> then it
    inherits all options set by the latter.  Additionally,
    <application>postgres</application>-specific options can be passed
    from the <application>postmaster</application> with the
    <option>-o</option> switch.
   </para>

   <para>
    You can avoid having to type these options by setting up a
    configuration file.  See the &cite-admin; for details.  Some
    (safe) options can also be set from the connecting client in an
    application-dependent way.  For example, if the environment
    variable <envar>PGOPTIONS</envar> is set, then
    <application>libpq</>-based clients will pass that string to the
    server, which will interpret it as
    <application>postgres</application> command-line options.
   </para>

   <refsect2>
    <title>General Purpose</title>

    <para>
     The options <option>-A</option>, <option>-B</option>,
     <option>-c</option>, <option>-d</option>, <option>-D</option>,
     <option>-F</option>, and <option>--name</> have the same meanings
     as the <xref linkend="app-postmaster"> except that
     <option>-d</option> <literal>0</> prevents the debugging level of
     the postmaster from being propagated to the backend.
    </para>

    <variablelist>
     <varlistentry>
      <term><option>-e</option></term>
      <listitem>
       <para>
        Sets the default date style to <quote>European</quote>, which
	means that the <quote>day before month</quote> (rather than
	month before day) rule is used to interpret ambiguous date
	input, and that the day is printed before the month in certain
	date output formats.  See the &cite-user; for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-o</option> <replaceable class="parameter">filename</replaceable></term>
      <listitem>
       <para>
	Sends all debugging and error output to 
	<replaceable class="parameter">filename</replaceable>.
	If the backend is running under the
	<application>postmaster</application>, this option is ignored,
	and the <systemitem>stderr</> inherited from the
	<application>postmaster</application> is used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-P</option></term>
      <listitem>
       <para>
	Ignore system indexes while scanning/updating system tuples. The
	<command>REINDEX</command> command for system tables/indexes
	requires this option to be used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-s</option></term>
      <listitem>
       <para>
	Print time information and other statistics at the end of each query.
	This is useful for benchmarking or for use in tuning the number of
	buffers.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-S</option> <replaceable class="parameter">sort-mem</replaceable></term>
      <listitem>
       <para>
	Specifies the amount of memory to be used by internal sorts and hashes
	before resorting to temporary disk files.  The value is specified in
	kilobytes, and defaults to 512 kilobytes.  Note that for a complex query,
	several sorts and/or hashes might be running in parallel, and each one
	will be allowed to use as much as
	<replaceable class="parameter">sort-mem</replaceable> kilobytes
	before it starts to put data into temporary files.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </refsect2>

   <refsect2>
    <title>Options for stand-alone mode</title>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">database</replaceable></term>
      <listitem>
       <para>
	Specifies the name of the database to be accessed.  If it is
	omitted it defaults to the user name.	
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-E</option></term>
      <listitem>
       <para>
	Echo all queries.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-N</option></term>
      <listitem>
       <para>
	Disables use of newline as a query delimiter.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </refsect2>

   <refsect2>
    <title>Semi-internal Options</title>

    <para>
     There are several other options that may be specified, used
     mainly for debugging purposes.  These are listed here only for
     the use by <productname>PostgreSQL</productname> system
     developers.  <emphasis>Use of any of these options is highly
     discouraged.</emphasis>  Furthermore, any of these options may
     disappear or change in a future release without notice.
   </para>
    <variablelist>

     <varlistentry>
      <term><option>-f</option> <literal>{ s | i | m | n | h }</literal></term>
      <listitem>
       <para>
	Forbids the use of particular scan and join methods:
	<literal>s</literal> and <literal>i</literal>
	disable sequential and index scans respectively, while
	<literal>n</literal>, <literal>m</literal>, and <literal>h</literal>
	disable nested-loop, merge and hash joins respectively.
	
	<note>
	 <para>
	  Neither sequential scans nor nested-loop joins can be disabled completely;
	  the <literal>-fs</literal> and <literal>-fn</literal>
	  options simply discourage the optimizer from using those
	  plan types if it has any other alternative.
	 </para>
	</note>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-i</option></term>
      <listitem>
       <para>
	Prevents query execution, but shows the plan tree.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-O</option></term>
      <listitem>
       <para>
	Allows the structure of system tables to be modified.  This is
	used by <application>initdb</application>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-p</option> <replaceable class="parameter">database</replaceable></term>
      <listitem>
       <para>
	Indicates that this server has been started by a
	<application>postmaster</application> and makes different
	assumptions about buffer pool management, file descriptors,
	etc.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-t</option> <literal>pa[rser] | pl[anner] | e[xecutor]</literal></term>
      <listitem>
       <para>
	Print timing statistics for each query relating to each of the
	major system modules.  This option cannot be used together
	with the <option>-s</option> option.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-v</option> <replaceable class="parameter">protocol</replaceable></term>
      <listitem>
       <para>
	Specifies the version number of the frontend/backend protocol
	to be used for this particular session.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-W</option> <replaceable class="parameter">seconds</replaceable></term>
      <listitem>
       <para>
	As soon as this option is encountered, the process sleeps for
	the specified amount of seconds.  This gives developers time
	to attach a debugger to the backend process.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </refsect2>
 </refsect1>

 <refsect1>
  <title>Environment</title>

  <variablelist>
   <varlistentry>
    <term><envar>PGDATA</envar></term>

    <listitem>
     <para>
      Default data direction location
     </para>
    </listitem>
   </varlistentry>

  </variablelist>

  <para>
   For others, which have little influence during single-user mode,
   see <xref linkend="app-postmaster">.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   To stop a running query use the <literal>SIGINT</literal> signal. To
   tell <application>postgres</application> to reread the config file,
   use a <literal>SIGHUP</literal> signal. The
   <application>postmaster</application> uses <literal>SIGTERM</literal>
   to tell a postgres process to quit normally and
   <literal>SIGQUIT</literal> to terminate without the normal cleanup.
   These <emphasis>should not</emphasis> be used by users.
  </para>

 </refsect1>

 <refsect1>
  <title>Usage</title>

   <para>
    Start a stand-alone backend with a command like
<screen>
<userinput>postgres -D $PGDATA <replaceable>other-options</> my_database</userinput>
</screen>
    Provide the correct path to the database area with <option>-D</>, or
    make sure that the environment variable <envar>PGDATA</> is set.
    Also specify the name of the particular database you want to work in.
   </para>

   <para>
    Normally, the stand-alone backend treats newline as the command
    entry terminator; there is no intelligence about semicolons,
    as there is in <application>psql</>.  To continue a command
    across multiple lines, you must type backslash just before each
    newline except the last one.
   </para>

   <para>
    But if you use the <option>-N</> command line switch, then newline does
    not terminate command entry.  The backend will read the standard input
    until the end-of-file (<acronym>EOF</>) marker, then
    process the input as a single query string.  Backslash-newline is not
    treated specially in this case.
   </para>

   <para>
    To quit the session, type <acronym>EOF</acronym>
    (<keycombo action="simul"><keycap>Control</><keycap>D</></>, usually).
    If you've
    used <option>-N</>, two consecutive <acronym>EOF</>s are needed to exit.
   </para>

   <para>
    Note that the stand-alone backend does not provide sophisticated
    line-editing features (no command history, for example).
   </para>

 </refsect1>

 <refsect1>
  <title>See Also</title>

  <para>
   <xref linkend="app-initdb">,
   <xref linkend="app-ipcclean">,
   <xref linkend="app-postmaster">
  </para>
 </refsect1>

</refentry>

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