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Postgres documentation
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<refentry id="APP-IPCCLEAN">
 <refmeta>
  <refentrytitle id="APP-IPCCLEAN-TITLE">
   <application>ipcclean</application>
  </refentrytitle>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   <application>ipcclean</application>
  </refname>
  <refpurpose>
   Clean up shared memory and semaphores from aborted backends
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>1999-07-20</date>
  </refsynopsisdivinfo>
  <synopsis>
ipcclean
  </synopsis>

  <refsect2 id="R2-APP-IPCCLEAN-1">
   <refsect2info>
    <date>1999-07-20</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>
    None.
   </para>
  </refsect2>

  <refsect2 id="R2-APP-IPCCLEAN-2">
   <refsect2info>
    <date>1999-07-30</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>
    None.
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-APP-IPCCLEAN-1">
  <refsect1info>
   <date>1999-07-20</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <application>ipcclean</application>
   cleans up shared memory and semaphore space from aborted backends by
   deleting all instances owned by user <literal>postgres</literal>.
   Only the DBA
   should execute this program as it can cause bizarre behavior (i.e.,
   crashes) if run during multi-user execution.  This program should be
   executed if messages such as

   <computeroutput>
semget: No space left on device
   </computeroutput>

   are encountered when starting up the 
   <application>postmaster</application> or the backend server.
  </para>

  <para>
   If this command is executed while <application>postmaster</application>
   is running, the shared memory and semaphores allocated by the
   <application>postmaster</application>
   will be deleted.  This will result in a general failure of the
   backends servers started by that
   <application>postmaster</application>.
  </para>

  <para>
   This script is a hack, but in the many years since it was written, no
   one has come up with an equally effective and portable solution.
   Suggestions are welcome.
  </para>

  <para>
   The script makes assumption about the format of output of the
   <application>ipcs</application>
   utility which may not be true across different operating systems.
   Therefore, it may not work on your particular OS.
  </para>
 </refsect1>
</refentry>

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