<!--
doc/src/sgml/ref/pg_checksums.sgml
PostgreSQL documentation
-->

<refentry id="app-pgchecksums">
 <indexterm zone="app-pgchecksums">
  <primary>pg_checksums</primary>
 </indexterm>

 <refmeta>
  <refentrytitle><application>pg_checksums</application></refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>pg_checksums</refname>
  <refpurpose>enable, disable or check data checksums in a <productname>PostgreSQL</productname> database cluster</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>pg_checksums</command>
   <arg rep="repeat" choice="opt"><replaceable class="parameter">option</replaceable></arg>
   <group choice="opt">
    <group choice="opt">
     <arg choice="plain"><option>-D</option></arg>
     <arg choice="plain"><option>--pgdata</option></arg>
    </group>
    <replaceable class="parameter"> datadir</replaceable>
   </group>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1 id="r1-app-pg_checksums-1">
  <title>Description</title>
  <para>
   <application>pg_checksums</application> checks, enables or disables data
   checksums in a <productname>PostgreSQL</productname> cluster.  The server
   must be shut down cleanly before running
   <application>pg_checksums</application>. The exit status is zero if there
   are no checksum errors when checking them, and nonzero if at least one
   checksum failure is detected. If enabling or disabling checksums, the
   exit status is nonzero if the operation failed.
  </para>

  <para>
   While checking or enabling checksums needs to scan or write every file in
   the cluster, disabling checksums will only update the file
   <filename>pg_control</filename>.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    The following command-line options are available:

    <variablelist>
     <varlistentry>
      <term><option>-D <replaceable>directory</replaceable></option></term>
      <term><option>--pgdata=<replaceable>directory</replaceable></option></term>
      <listitem>
       <para>
        Specifies the directory where the database cluster is stored.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-c</option></term>
      <term><option>--check</option></term>
      <listitem>
       <para>
        Checks checksums. This is the default mode if nothing else is
        specified.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-d</option></term>
      <term><option>--disable</option></term>
      <listitem>
       <para>
        Disables checksums.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-e</option></term>
      <term><option>--enable</option></term>
      <listitem>
       <para>
        Enables checksums.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-N</option></term>
      <term><option>--no-sync</option></term>
      <listitem>
       <para>
        By default, <command>pg_checksums</command> will wait for all files
        to be written safely to disk.  This option causes
        <command>pg_checksums</command> to return without waiting, which is
        faster, but means that a subsequent operating system crash can leave
        the updated data folder corrupt.  Generally, this option is useful
        for testing but should not be used on a production installation.
        This option has no effect when using <literal>--check</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-v</option></term>
      <term><option>--verbose</option></term>
      <listitem>
       <para>
        Enable verbose output. Lists all checked files.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-r <replaceable>relfilenode</replaceable></option></term>
      <listitem>
       <para>
        Only validate checksums in the relation with specified relfilenode.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
       <term><option>-V</option></term>
       <term><option>--version</option></term>
       <listitem>
       <para>
        Print the <application>pg_checksums</application> version and exit.
       </para>
       </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-?</option></term>
      <term><option>--help</option></term>
       <listitem>
        <para>
         Show help about <application>pg_checksums</application> command line
         arguments, and exit.
        </para>
       </listitem>
      </varlistentry>
    </variablelist>
   </para>
 </refsect1>

 <refsect1>
  <title>Environment</title>

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

    <listitem>
     <para>
      Specifies the directory where the database cluster is
      stored; can be overridden using the <option>-D</option> option.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>
  <para>
   Enabling checksums in a large cluster can potentially take a long time.
   During this operation, the cluster or other programs that write to the
   data directory must not be started or else data loss may occur.
  </para>
  <para>
   When using a replication setup with tools which perform direct copies
   of relation file blocks (for example <xref linkend="app-pgrewind"/>),
   enabling or disabling checksums can lead to page corruptions in the
   shape of incorrect checksums if the operation is not done consistently
   across all nodes. When enabling or disabling checksums in a replication
   setup, it is thus recommended to stop all the clusters before switching
   them all consistently. Destroying all standbys, performing the operation
   on the primary and finally recreating the standbys from scratch is also
   safe.
  </para>
  <para>
   If <application>pg_checksums</application> is aborted or killed while
   enabling or disabling checksums, the cluster will keep the same
   configuration for data checksums as before the operation attempted.
   <application>pg_checksums</application> can be restarted to
   attempt again the same operation.
  </para>
 </refsect1>
</refentry>
