nix-super/doc/manual/troubleshooting.xml

<appendix>
  <title>Troubleshooting</title>

  <sect1>
    <title>Database hangs</title>

    <para>
      If Nix or Fix appear to hang immediately after they are started, Nix's
      database is probably <quote>wedged</quote>, i.e., some process died while
      it held a lock on the database.  The solution is to ensure that no other
      processes are accessing the database and then run the following command:
    </para>

    <screen>
      $ db_recover -e -h <replaceable>prefix</replaceable>/var/nix/db</screen>

    <para>
      Here, <replaceable>prefix</replaceable> should be replaced by Nix's
      installation prefix.
    </para>

  </sect1>


  <sect1>
    <title>Database logfile removal</title>

    <para>
      Every time a Nix database transaction takes place, Nix writes a record of
      this transaction to a <emphasis>log</emphasis> in its database directory
      to ensure that the operation can be replayed in case of a application or
      system crash.  However, without manual intervention, the log grows
      indefinitely.  Hence, unused log files should be deleted periodically.
      This can be accomplished using the following command:
    </para>

    <screen>
      $ rm `db_archive -a -h <replaceable>prefix</replaceable>/var/nix/db`</screen>

  </sect1>
	
</appendix>

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