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$Header: /cvsroot/pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.16 2000/11/22 01:41:13 momjian Exp $
Postgres documentation
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<refentry id="APP-POSTMASTER">
 <docinfo>
  <date>2000-11-12</date>
 </docinfo>

 <refmeta>
  <refentrytitle id="APP-POSTMASTER-TITLE"><application>postmaster</application></refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname id="postmaster-ref">postmaster</refname>
  <refpurpose><productname>PostgreSQL</productname> multi-user database server</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>postmaster</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>-F</arg>
   <arg>-h <replaceable>hostname</replaceable></arg>
   <arg>-i</arg>
   <arg>-k <replaceable>filename</replaceable></arg>
   <arg>-l</arg>
   <arg>-N <replaceable>max-connections</replaceable></arg>
   <arg>-o <replaceable>extra-options</replaceable></arg>
   <arg>-p <replaceable>port</replaceable></arg>
   <arg>-S</arg>
   <group><arg>-n</arg><arg>-s</arg></group>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <application>postmaster</application> is the
   <productname>PostgreSQL</productname> multi-user database server.
   In order for a client application to access a database it connects
   (over a network or locally) to a running
   <application>postmaster</application>.  The
   <application>postmaster</application> then starts a separate server
   process (<quote><xref linkend="app-postgres"
   endterm="app-postgres-title"></quote>) to handle the connection.
   The postmaster also manages the communication among server
   processes.
  </para>

  <para>
   By default the postmaster starts in the foreground and prints log
   messages to the standard output.  In practical applications the
   postmaster should be started as a background process, perhaps at
   boot time.
  </para>

  <para>
   One postmaster always manages the data from exactly one database
   cluster.  A database cluster is a collection of databases that is
   stored at a common file system location.  When the postmaster
   starts it needs to know the location of the database cluster files
   (<quote>data area</quote>).  This is done with the
   <option>-D</option> invocation option or the <envar>PGDATA</envar>
   environment variable, there is no default.  More than one
   postmaster process can run on a system at one time, as long as they
   use different data areas and different port numbers (see below).  A
   data area is created with <xref linkend="app-initdb"
   endterm="app-initdb-title">.
  </para>

  <refsect2 id="app-postmaster-options">
   <title>Options</title>
   <para>
    <application>postmaster</application> accepts the following
    command line arguments.  For a detailed discussion of the options
    consult the <citetitle>Administrator's Guide</citetitle>.  You can
    also save typing most of these options by setting up a
    configuration file.
    
    <variablelist>
     <varlistentry>
      <term>-A 0|1</term>
      <listitem>
       <para>
        Enables run-time assert checks, which is a debugging aid to
        detect programming mistakes.  This is only available if it was
        enabled during compilation.  If so, the default is on.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-B <replaceable class="parameter">nbuffers</replaceable></term>
      <listitem>
       <para>
	Sets the number of shared buffers for use by the server
	processes.  This value defaults to 64 buffers, where each
	buffer is 8 kB.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></term>
      <listitem>
       <para>
        Sets a named run-time parameter. Consult the
        <citetitle>Administrator's Guide</citetitle> for a list and
        descriptions.  Most of the other command line options are in
        fact short forms of such a parameter assignment.
       </para>

       <para>
        On some systems it is also possible to equivalently use
        GNU-style long options in the form
        <literal>--name=value</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-d <replaceable>debug-level</replaceable></term>
      <listitem>
       <para>
        Sets the debug level.  The higher this value is set, the more
        debugging output is written to the server log.  The default is
        0, which means no debugging.  Values up to 4 make sense.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-D <replaceable class="parameter">datadir</replaceable></term>
      <listitem>
       <para>
	Specifies the file system location of the data directory.  See
	discussion above.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-F</term>
      <listitem>
       <para>
        Disables <function>fsync</function> calls for performance
        improvement at the risk of data corruption.  Read the detailed
        documentation before using this!
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-h <replaceable class="parameter">hostname</replaceable></term>
      <listitem>
       <para>
	Specifies the TCP/IP hostname or address on which the
	<application>postmaster</application> is to listen for
	connections from client applications.  Defaults to the value
	of the <envar>PGHOST</envar> environment variable, or if
	<envar>PGHOST</envar> is not set, it defaults to listening on
	all configured addresses (including localhost).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-i</term>
      <listitem>
       <para>
        Allows clients to connect via TCP/IP (Internet domain)
	connections.  Without this option, only local Unix domain
	socket connections are accepted.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-k <replaceable class="parameter">filename</replaceable></term>
      <listitem>
       <para>
	Specifies the directory for Unix domain socket on which the
	<application>postmaster</application> is to listen for
	connections from client applications.  Defaults to the value
	of the <envar>PGUNIXSOCKET</envar> environment variable, or if
	<envar>PGUNIXSOCKET</envar> is not set, then defaults to a
	file in <filename>/tmp</filename>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-l</term>
      <listitem>
       <para>
	Enables secure connections using SSL.  The <option>-i</option>
	option is also required.  You must have compiled with SSL
	enabled to use this option.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-N <replaceable class="parameter">max-connections</replaceable></term>
      <listitem>
       <para>
	Sets the maximum number of client connections that this
	postmaster will accept.  By default, this value is 32, but it
	can be set as high as 1024 if your system will support that
	many processes.  (Note that <option>-B</option> is required to
	be at least twice <option>-N</option>.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-o <replaceable class="parameter">extra-options</replaceable></term>
      <listitem>
       <para>
	The command line-style options specified in <replaceable
	class="parameter">EXTRA-OPTIONS</replaceable> are passed to
	all backend server processes started by this
	<application>postmaster</application>.  See <xref
	linkend="app-postgres" endterm="app-postgres-title"> for
	possibilities.  If the option string contains any spaces, the
	entire string must be quoted.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-p <replaceable class="parameter">port</replaceable></term>
      <listitem>
       <para>
	Specifies the TCP/IP port or local Unix domain socket file
	extension on which the <application>postmaster</application>
	is to listen for connections from client applications.
	Defaults to the value of the <envar>PGPORT</envar> environment
	variable, or if <envar>PGPORT</envar> is not set, then
	defaults to the value established during compilation (normally
	5432).  If you specify a port other than the default port,
	then all client applications must specify the same port using
	either command-line options or <envar>PGPORT</envar>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-S</term>
      <listitem>
       <para>
	Specifies that the <application>postmaster</application>
	process should start up in silent mode.  That is, it will
	disassociate from the user's (controlling) terminal, start its
	own process group, and redirect its standard output and
	standard error to <filename>/dev/null</filename>.
       </para>
       <para>
        Using this switch discards all logging output, which is
	probably not what you want, since it makes it very difficult
	to troubleshoot problems.  See below for a better way to start
	the postmaster in the background.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </para>

   <para>
    Two additional command line options are available for debugging
    problems that cause a backend to die abnormally.  These options
    control the behavior of the <application>postmaster</application>
    in this situation, and <emphasis>neither option is intended for
    use in ordinary operation</emphasis>.
   </para>

   <para>
    The ordinary strategy for this situation is to notify all other
    backends that they must terminate and then reinitialize the shared
    memory and semaphores.  This is because an errant backend could
    have corrupted some shared state before terminating.
   </para>

   <para>
    These special-case options are:

    <variablelist>
     <varlistentry>
      <term>-n</term>
      <listitem>
       <para>
	<application>postmaster</application>
	will not reinitialize shared data structures.  A knowledgeable system
	programmer can then use a debugger
	to examine shared memory and semaphore state.
       </para>
     </listitem>
    </varlistentry>

    <varlistentry>
      <term>-s</term>
      <listitem>
       <para>
	<application>postmaster</application>
	will stop all other backend processes by sending the signal
	<literal>SIGSTOP</literal>,
	but will not cause them to terminate.  This permits system programmers
	to collect core dumps from all backend processes by hand.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-APP-POSTMASTER-2">
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>
semget: No space left on device
       </computeroutput></term>
      <listitem>
       <para>
	If you see this message, you should run the
	<application>ipcclean</application>
	command.  After doing so, try starting
	<application>postmaster</application>
	again.  If this still doesn't work, you probably need to configure
	your kernel for shared memory and semaphores as described in the
	installation notes.  If you run multiple instances of
	<application>postmaster</application>
	on a single host, or have a kernel with particularly small shared memory
	and/or semaphore limits, you may have to reconfigure your kernel to increase
	its shared memory or semaphore parameters.

	<tip>
	 <para>
	  You may be able to postpone
	  reconfiguring your kernel by decreasing -B to reduce
	  <productname>Postgres</productname>' shared memory
	  consumption, and/or by reducing -N to reduce Postgres' semaphore
	  consumption.
	 </para>
	</tip>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
StreamServerPort: cannot bind to port
       </computeroutput></term>
      <listitem>
       <para>
	If you see this message, you should make certain that there is no
	other <application>postmaster</application>
	process already running on the same port number.  The easiest way to
	determine this is by using the command
	<programlisting>
$ ps -ax | grep postmaster
	</programlisting>
on BSD-based systems, or
	<programlisting>
$ ps -e | grep postmast
	</programlisting>
	for System V-like or POSIX-compliant systems such as HP-UX.
       </para>

       <para>
	If you 
	are sure that no other
	<application>postmaster</application>
	processes are running and you still get this error, try specifying a
	different port using the
	<literal>-p</literal>
	option.  You may also get this error if you terminate the
	<application>postmaster</application>
	and immediately restart it using the same port; in this case, you must
	simply wait a few seconds until the operating system closes the port
	before trying again.  Finally, you may get this error if you specify
	a port number that your operating system considers to be reserved.
	For example, many versions of Unix consider port numbers under 1024 to
	be <firstterm>trusted</firstterm>
	and only permit the Unix superuser to access them.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
IpcMemoryAttach: shmat() failed: Permission denied
       </computeroutput></term>
      <listitem>
       <para>
	A likely explanation is that another user attempted to start a
	<application>postmaster</application>
	process on the same port which acquired shared resources and then 
	died.  Since Postgres shared memory keys are based on the port number 
	assigned to the
	<application>postmaster</application>,
	such conflicts are likely if there is more than one installation on 
	a single host.  If there are no other
	<application>postmaster</application>
	processes currently running (see above), run
	<application>ipcclean</application>
	and try again.  If other <application>postmaster</application>
	images
	are running, you will have to find the owners of those processes to
	coordinate the assignment of port numbers and/or removal of unused
	shared memory segments.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsect1>

 <refsect1>
  <title>Notes</title>
  
  <para>
   If at all possible, <emphasis>do not</emphasis> use
   <literal>SIGKILL</literal> to kill the
   <application>postmaster</application>.  This will prevent
   <application>postmaster</application> from freeing the system
   resources (e.g., shared memory and semaphores) that it holds before
   terminating.
  </para>

  <para>
   To terminate the postmaster normally, the signals
   <literal>SIGTERM</literal>, <literal>SIGINT</literal>, or
   <literal>SIGQUIT</literal> can be used.  The first will wait for
   all clients to terminate before quitting, the second will
   forcefully disconnect all clients, and the third will quit
   immediately without lengthy shutdown, resulting in a recovery run
   during restart.
  </para>

  <para>
   The utility command <xref linkend="app-pg-ctl"> can be used to
   start and shut down the postmaster safely and comfortably.
  </para>
 </refsect1>

 <refsect1 id="app-postmaster-usage">
  <title>Usage</title>
  <para>
   To start <application>postmaster</application> in the background
   using default values, type:

<screen>
<prompt>$</prompt> <userinput>nohup postmaster &gt;logfile 2&gt;&amp;1 &lt;/dev/null &amp;</userinput>
</screen>
  </para>

  <para>
   To start <application>postmaster</application> with a specific
   port:
<screen>
<prompt>$</prompt> <userinput>postmaster -p 1234</userinput>
</screen>
   This command will start up <application>postmaster</application>
   communicating through the port 1234. In order to connect to this
   <application>postmaster</application> using psql, you would need to
   run it as
<screen>
<prompt>$</prompt> <userinput>psql -p 1234</userinput>
</screen>
   or set the environment variable <envar>PGPORT</envar>:
<screen>
<prompt>$</prompt> <userinput>export PGPORT=1234</userinput>
<prompt>$</prompt> <userinput>psql</userinput>
</screen>
  </para>
 </refsect1>
</refentry>

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