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$PostgreSQL: pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.45 2004/02/03 17:34:02 tgl Exp $
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<refentry id="app-postmaster">
 <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> multiuser database server</refpurpose>
 </refnamediv>

 <indexterm zone="app-postmaster">
  <primary>postmaster</primary>
 </indexterm>

 <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>directory</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>
   <arg>--<replaceable>name</replaceable>=<replaceable>value</replaceable></arg>
   <group><arg>-n</arg><arg>-s</arg></group>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

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

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

  <para>
   One <command>postmaster</command> 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 <command>postmaster</command> 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 <command>postmaster</command> process can run on a system at one time,
   as long as they use different data areas and different
   communication ports (see below).  A data area is created with <xref
   linkend="app-initdb">.
  </para>
 </refsect1>

 <refsect1 id="app-postmaster-options">
  <title>Options</title>

   <para>
    <command>postmaster</command> accepts the following
    command line arguments.  For a detailed discussion of the options
    consult <xref linkend="runtime-config">.  You can also save typing most of these
    options by setting up a configuration file.
    
    <variablelist>
     <varlistentry>
      <term><option>-A 0|1</option></term>
      <listitem>
       <para>
        Enables run-time assertion 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><option>-B <replaceable class="parameter">nbuffers</replaceable></option></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><option>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></option></term>
      <listitem>
       <para>
        Sets a named run-time parameter. Consult <xref linkend="runtime-config"> for
        a list and descriptions.  Most of the other command line
        options are in fact short forms of such a parameter
        assignment.  <option>-c</> can appear multiple times to set
        multiple parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-d <replaceable>debug-level</replaceable></option></term>
      <listitem>
       <para>
        Sets the debug level.  The higher this value is set, the more
        debugging output is written to the server log.  Values are from
	1 to 5.
       </para>
      </listitem>
     </varlistentry>

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

     <varlistentry>
      <term><option>-F</option></term>
      <listitem>
       <para>
        Disables <function>fsync</function> calls for performance
        improvement, at the risk of data corruption in event of a
        system crash.  This option corresponds to setting
        <literal>fsync=false</> in <filename>postgresql.conf</>. Read the detailed
        documentation before using this!
       </para>
       <para>
        <option>--fsync=true</option> has the opposite effect
        of this option.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-h <replaceable class="parameter">hostname</replaceable></option></term>
      <listitem>
       <para>
	Specifies the IP host name or address on which the
	<command>postmaster</command> is to listen for
	connections from client applications.  Defaults to
	listening on all configured addresses (including
        <systemitem class="systemname">localhost</systemitem>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-i</option></term>
      <listitem>
       <para>
        Allows clients to connect via TCP/IP (Internet domain)
	connections.  Without this option, only local Unix domain
        socket connections are accepted. This option corresponds
        to setting <literal>tcpip_socket=true</> in <filename>postgresql.conf</>.
       </para>
       <para>
        <option>--tcpip-socket=false</option> has the opposite
        effect of this option.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-k <replaceable class="parameter">directory</replaceable></option></term>
      <listitem>
       <para>
	Specifies the directory of the Unix-domain socket on which the
	<command>postmaster</command> is to listen for
	connections from client applications.  The default is normally
	<filename>/tmp</filename>, but can be changed at build time.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-l</option></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><option>-N <replaceable class="parameter">max-connections</replaceable></option></term>
      <listitem>
       <para>
	Sets the maximum number of client connections that this
	<command>postmaster</command> will accept.  By
	default, this value is 32, but it can be set as high as your
	system will support.  (Note that
	<option>-B</option> is required to be at least twice
	<option>-N</option>.  See <xref linkend="kernel-resources"> for a discussion of
	system resource requirements for large numbers of client
	connections.)
       </para>
      </listitem>
     </varlistentry>

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

     <varlistentry>
      <term><option>-p <replaceable class="parameter">port</replaceable></option></term>
      <listitem>
       <para>
	Specifies the TCP/IP port or local Unix domain socket file
	extension on which the <command>postmaster</command>
	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><option>-S</option></term>
      <listitem>
       <para>
	Specifies that the <command>postmaster</command>
	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 <command>postmaster</command> in the background.
       </para>
       <para>
        <option>--silent-mode=false</option> has the opposite effect
        of this option.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--<replaceable>name</replaceable>=<replaceable>value</replaceable></option></term>
      <listitem>
       <para>
        Sets a named run-time parameter; a shorter form of
        <option>-c</>.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </para>

   <para>
    Two additional command line options are available for debugging
    problems that cause a server process to die abnormally.  The
    ordinary strategy in this situation is to notify all other server
    processes that they must terminate and then reinitialize the
    shared memory and semaphores.  This is because an errant server
    process could have corrupted some shared state before terminating.
    These options select alternative behaviors of the
    <command>postmaster</command> in this situation.
    <emphasis>Neither option is intended for use in ordinary
    operation.</emphasis>
   </para>

   <para>
   </para>

   <para>
    These special-case options are:

    <variablelist>
     <varlistentry>
      <term><option>-n</option></term>
      <listitem>
       <para>
	<command>postmaster</command>
	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><option>-s</option></term>
      <listitem>
       <para>
	<command>postmaster</command>
	will stop all other server 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 server processes by hand.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

 </refsect1>

 <refsect1>
  <title>Environment</title>

  <variablelist>
   <varlistentry>
    <term><envar>PGCLIENTENCODING</envar></term>

    <listitem>
     <para>
      Default character encoding used by clients.  (The clients may
      override this individually.)  This value can also be set in the
      configuration file.
     </para>
    </listitem>
   </varlistentry>

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

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

   <varlistentry>
    <term><envar>PGDATESTYLE</envar></term>

    <listitem>
     <para>
      Default value of the <varname>DateStyle</varname> run-time
      parameter.  (The use of this environment variable is deprecated.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><envar>PGPORT</envar></term>

    <listitem>
     <para>
      Default port (preferably set in the configuration file)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><envar>TZ</envar></term>

    <listitem>
     <para>
      Server time zone
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>others</term>

    <listitem>
     <para>
      Other environment variables may be used to designate alternative
      data storage locations.  See <xref linkend="manage-ag-alternate-locs"> for more
      information.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1>
   <title>Diagnostics</title>

   <para>
    A failure message mentioning <literal>semget</> or <literal>shmget</>
    probably indicates you need to configure your kernel to provide adequate
    shared memory and semaphores.  For more discussion see <xref
    linkend="kernel-resources">.
   </para>

   <tip>
    <para>
     You may be able to postpone reconfiguring your kernel by decreasing
     <varname>shared_buffers</varname> to reduce the shared memory consumption
     of <productname>PostgreSQL</>, and/or by reducing
     <varname>max_connections</varname> to reduce the semaphore consumption.
    </para>
   </tip>

   <para>
    A failure message suggesting that another postmaster is already running
    should be checked carefully, for example by using the command
<screen>
<prompt>$</prompt> <userinput>ps ax | grep postmaster</userinput>
</screen>
        or
<screen>
<prompt>$</prompt> <userinput>ps -ef | grep postmaster</userinput>
</screen>
    depending on your system.  If you are certain that no conflicting
    postmaster is running, you may remove the lock file mentioned in the
    message and try again.
   </para>

   <para>
    A failure message indicating inability to bind to a port may
    indicate that that port is already in use by some
    non-<productname>PostgreSQL</productname> process.  You may also
    get this error if you terminate the <command>postmaster</command>
    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 <quote>trusted</quote> and only permit
    the Unix superuser to access them.
   </para>

 </refsect1>

 <refsect1>
  <title>Notes</title>
  
  <para>
   If at all possible, <emphasis>do not</emphasis> use
   <literal>SIGKILL</literal> to kill the
   <command>postmaster</command>.  Doing so will prevent
   <command>postmaster</command> from freeing the system
   resources (e.g., shared memory and semaphores) that it holds before
   terminating.  This may cause problems for starting a fresh
   <command>postmaster</command> run.
  </para>

  <para>
   To terminate the <command>postmaster</command> 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 proper shutdown, resulting in a recovery run
   during restart.   The <literal>SIGHUP</literal> signal will 
   reload the server configuration files.
  </para>

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

  <para>
   The <option>--</> options will not work on <systemitem
   class="osname">FreeBSD</> or <systemitem class="osname">OpenBSD</>.
   Use <option>-c</> instead. This is a bug in the affected operating
   systems; a future release of <productname>PostgreSQL</productname>
   will provide a workaround if this is not fixed.
  </para>

 </refsect1>

 <refsect1 id="app-postmaster-examples">
  <title>Examples</title>
  <para>
   To start <command>postmaster</command> 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 <command>postmaster</command> with a specific
   port:
<screen>
<prompt>$</prompt> <userinput>postmaster -p 1234</userinput>
</screen>
   This command will start up <command>postmaster</command>
   communicating through the port 1234. In order to connect to this
   <command>postmaster</command> using <application>psql</>, you would need to
   run it as
<screen>
<prompt>$</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>

  <para>
   Named run-time parameters can be set in either of these styles:
<screen>
<prompt>$</prompt> <userinput>postmaster -c work_mem=1234</userinput>
<prompt>$</prompt> <userinput>postmaster --work-mem=1234</userinput>
</screen>
   Either form overrides whatever setting might exist for <varname>work_mem</>
   in <filename>postgresql.conf</>.  Notice that underscores in parameter
   names can be written as either underscore or dash on the command line.
  </para>

  <tip>
  <para>
   Except for short-term experiments,
   it's probably better practice to edit the setting in
   <filename>postgresql.conf</> than to rely on a command-line switch
   to set a parameter.
  </para>
  </tip>
 </refsect1>

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

  <para>
   <xref linkend="app-initdb">,
   <xref linkend="app-pg-ctl">
  </para>
 </refsect1>
</refentry>

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