<listitem>
       <para>
        The default shared memory settings are usually good enough, unless
        you have set <literal>shared_memory_type</literal> to <literal>sysv</literal>.
        However, you will need to
        increase <literal>kern.seminfo.semmni</literal>
        and <literal>kern.seminfo.semmns</literal>,
        as <systemitem class="osname">OpenBSD</systemitem>'s default settings
        for these are unworkably small.
       </para>

       <para>
        IPC parameters can be adjusted using <command>sysctl</command>,
        for example:
<screen>
<prompt>#</prompt> <userinput>sysctl kern.seminfo.semmni=100</userinput>
</screen>
        To make these settings persist over reboots, modify
        <filename>/etc/sysctl.conf</filename>.
       </para>

      </listitem>
     </varlistentry>

     <varlistentry>
      <term><systemitem class="osname">Linux</systemitem>
      <indexterm><primary>Linux</primary><secondary>IPC configuration</secondary></indexterm>
      </term>
      <listitem>
       <para>
        The default shared memory settings are usually good enough, unless
        you have set <literal>shared_memory_type</literal> to <literal>sysv</literal>,
        and even then only on older kernel versions that shipped with low defaults.
        System V semaphores are not used on this platform.
       </para>

       <para>
        The shared memory size settings can be changed via the
        <command>sysctl</command> interface.  For example, to allow 16 GB:
<screen>
<prompt>$</prompt> <userinput>sysctl -w kernel.shmmax=17179869184</userinput>
<prompt>$</prompt> <userinput>sysctl -w kernel.shmall=4194304</userinput>
</screen>
        To make these settings persist over reboots, see
        <filename>/etc/sysctl.conf</filename>.
       </para>

      </listitem>
     </varlistentry>


     <varlistentry>
      <term><systemitem class="osname">macOS</systemitem>
      <indexterm><primary>macOS</primary><secondary>IPC configuration</secondary></indexterm>
      </term>
      <listitem>
       <para>
        The default shared memory and semaphore settings are usually good enough, unless
        you have set <literal>shared_memory_type</literal> to <literal>sysv</literal>.
       </para>
       <para>
        The recommended method for configuring shared memory in macOS
        is to create a file named <filename>/etc/sysctl.conf</filename>,
        containing variable assignments such as:
<programlisting>
kern.sysv.shmmax=4194304
kern.sysv.shmmin=1
kern.sysv.shmmni=32
kern.sysv.shmseg=8
kern.sysv.shmall=1024
</programlisting>
        Note that in some macOS versions,
        <emphasis>all five</emphasis> shared-memory parameters must be set in
        <filename>/etc/sysctl.conf</filename>, else the values will be ignored.
       </para>

       <para>
        <varname>SHMMAX</varname> can only be set to a multiple of 4096.
       </para>

       <para>
        <varname>SHMALL</varname> is measured in 4 kB pages on this platform.
       </para>

       <para>
        It is possible to change all but <varname>SHMMNI</varname> on the fly, using
        <application>sysctl</application>.  But it's still best to set up your preferred
        values via <filename>/etc/sysctl.conf</filename>, so that the values will be
        kept across reboots.
       </para>

      </listitem>
     </varlistentry>

     <varlistentry>
      <term><systemitem class="osname">Solaris</systemitem></term>
      <term><systemitem class="osname">illumos</systemitem></term>
      <listitem>
       <para>
        The default shared memory and semaphore settings are usually good enough for most
        <productname>PostgreSQL</productname> applications.  Solaris defaults
        to a <varname>SHMMAX</varname> of one-quarter of system <acronym>RAM</acronym>.
        To further adjust this setting, use a project setting associated
        with the <literal>postgres</literal> user.  For example, run the
        following as <literal>root</literal>: