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<page title="Debian Tips">

<h1 align=center>semget: No space left on device</h1>

<p>On servers that run for a long period of time you may encounter an
error message like the following.</p>

<p><pre>
   semget: No space left on device
</pre></p>

<p>Common places are the error.log from Apache or the postgresql.log,
combined with the associated program not starting anymore.  The cause
seems to be that programs that didn't terminate properly still "use"
semaphores in the kernel, although the corresponding process does not
exist anymore.  Semaphores are used for inter-process synchronisation.
</p>

<p>If you have PostgreSQL installed, there is an easy way to get this
problem solved.  The <a
href="http://www.postgresql.ps.pl/users-lounge/docs/7.1/reference/app-ipcclean.html">\
ipcclean</a>  program removes all shared memory segments and semaphore
sets owned by the current user.  Hence the solution is:</p>

<p><ul>

<li> If you are running PostgreSQL, stop the currently running
     postmaster and associated processes.  Then change the userid to
     postgres, the user PostgreSQL runs as, and execute the <code>\
     ipcclean</code> program.

<li> If you are running Apache as well, stop the Apache server, change
     the userid to www-data and execute the <code>ipcclean</code>
     program.

</ul></p>

<p>If you would like to clean the semaphore pool on a regular bases,
the following script snippet could be used in a cron job:</p>

<p><pre>
   apachectl stop
   su - -c /usr/lib/postgresql/bin/ipcclean www-data
   apachectl start
</pre></p>

<p>Please take into account that this will create a massive amount of
output, so you should probably redirect the output to <code>\
/dev/null</code> or into a log file at your convenience.</p>

</page>

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