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<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2021</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
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    </legalnotice>

    <title>os_sup</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module since="">os_sup</module>
  <modulesummary>Interface to OS System Messages</modulesummary>
  <description>
    <p><c>os_sup</c> is a process providing a message passing service
      from the operating system to the error logger in the Erlang
      runtime system. It is part of the OS_Mon application, see
      <seeapp marker="os_mon_app">os_mon(6)</seeapp>. Available for
      Solaris and Windows.</p>
    <p>Messages received from the operating system results in an
      user defined callback function being called. This function can do
      whatever filtering and formatting is necessary and then deploy any
      type of logging suitable for the user's application.</p>
  </description>

  <section>
    <title>Solaris Operation</title>
    <p>The Solaris (SunOS 5.x) messages are retrieved from
      the syslog daemon, <c>syslogd</c>.</p>
    <p>Enabling the service includes actions which require root
      privileges, such as change of ownership and file privileges of an
      executable binary file, and creating a modified copy of
      the configuration file for <c>syslogd</c>. When <c>os_sup</c> is
      terminated, the service must be disabled, meaning the original
      configuration must be restored. Enabling/disabling can be done
      either outside or inside <c>os_sup</c>. See
      <seeerl marker="#config">Configuration</seeerl> below.</p>
    <warning>
      <p>This process cannot run in multiple instances on the same
        hardware. OS_Mon must be configured to start <c>os_sup</c> on
        one node only if two or more Erlang nodes execute on the same
        machine.</p>
    </warning>
    <p>The format of received events is not defined.</p>
  </section>

  <section>
    <title>Windows Operation</title>
    <p>The Windows messages are retrieved from the eventlog file.</p>
    <p>The <c>nteventlog</c> module is used to implement <c>os_sup</c>.
      See <seeerl marker="nteventlog">nteventlog(3)</seeerl>. Note
      that the start functions of <c>nteventlog</c> does not need to be
      used, as in this case the process is started automatically as part of
      the OS_Mon supervision tree.</p>
    <p>OS messages are formatted as a tuple
      <c>{Time, Category, Facility, Severity, Message}</c>:</p>
    <taglist>
      <tag><c>Time = {MegaSecs, Secs, MicroSecs}</c></tag>
      <item>
        <p>A time stamp as returned by the BIF <c>now()</c>.</p>
      </item>
      <tag><c>Category = string()</c></tag>
      <item>
        <p>Usually one of <c>"System"</c>, <c>"Application"</c> or
          <c>"Security"</c>. Note that the NT eventlog viewer has
          another notion of category, which in most cases is totally
          meaningless and therefore not imported into Erlang. What is
          called a category here is one of the main three types of
          events occurring in a normal NT system.</p>
      </item>
      <tag><c>Facility = string()</c></tag>
      <item>
        <p>The source of the message, usually the name of
          the application that generated it. This could be almost any
          string. When matching messages from certain applications,
          the version number of the application may have to be
          accounted for. This is what the NT event viewer calls
          "source".</p>
      </item>
      <tag><c>Severity = string()</c></tag>
      <item>
        <p>One of <c>"Error"</c>, <c>"Warning"</c>,
          <c>"Informational"</c>, <c>"Audit_Success"</c>,
          <c>"Audit_Faulure"</c> or, in case of a currently unknown
          Windows NT version <c>"Severity_Unknown"</c>.</p>
      </item>
      <tag><c>Message = string()</c></tag>
      <item>
        <p>Formatted exactly as it would be in the NT eventlog viewer.
          Binary data is not imported into Erlang.</p>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="config"></marker>
    <title>Configuration</title>
    <taglist>
      <tag><c>os_sup_mfa = {Module, Function, Args}</c></tag>
      <item>
        <p>The callback function to use. <c>Module</c> and
          <c>Function</c> are atoms and <c>Args</c> is a list of terms.
          When an OS message <c>Msg</c> is received, this function is
          called as <c>apply(Module, Function, [Msg | Args])</c>.</p>
        <p>Default is <c>{os_sup, error_report, [Tag]}</c> which will
          send the event to the error logger using
          <seemfa marker="kernel:error_logger#error_report/2">error_logger:error_report(Tag, Msg)</seemfa>. <c>Tag</c> is the value of
          <c>os_sup_errortag</c>, see below.</p>
      </item>
      <tag><c>os_sup_errortag = atom()</c></tag>
      <item>
        <p>This parameter defines the error report type used when
          messages are sent to error logger using the default callback
          function. Default is <c>std_error</c>, which means the events
          are handled by the standard event handler.</p>
      </item>
      <tag><c>os_sup_enable = bool()</c></tag>
      <item>
        <p>Solaris only. Defines if the service should be enabled (and
          disabled) inside (<c>true</c>) or outside (<c>false</c>)
          <c>os_sup</c>. For backwards compatibility reasons,
          the default is <c>true</c>. The recommended value is
          <c>false</c>, as the Erlang emulator should normally not be
          run with <c>root</c> privileges, as is required for enabling
          the service.</p>
      </item>
      <tag><c>os_sup_own = string()</c></tag>
      <item>
        <p>Solaris only. Defines the directory which contains
          the backup copy and the Erlang specific configuration files
          for <c>syslogd</c>, and a named pipe to receive the messages
          from <c>syslogd</c>. Default is <c>"/etc"</c>.</p>
      </item>
      <tag><c>os_sup_syslogconf = string()</c></tag>
      <item>
        <p>Solaris only. Defines the full name of the configuration file
          for <c>syslogd</c>. Default is <c>"/etc/syslog.conf"</c>.</p>
      </item>
    </taglist>
  </section>
  <funcs>
    <func>
      <name since="">enable() -> ok | {error, Res}</name>
      <name since="">enable(Dir, Conf) -> ok | {error, Error}</name>
      <fsummary>Enable the service (Solaris only)</fsummary>
      <type>
        <v>Dir = Conf = Res = string()</v>
      </type>
      <desc>
        <p>Enables the <c>os_sup</c> service. Needed on Solaris only.</p>
        <p>If the configuration parameter <c>os_sup_enable</c> is
          <c>false</c>, this function is called automatically by
          <c>os_sup</c>, using the values of <c>os_sup_own</c> and
          <c>os_sup_syslogconf</c> as arguments.</p>
        <p>If <c>os_sup_enable</c> is <c>true</c>, this function must
          be called <em>before</em> OS_Mon/<c>os_sup</c> is started.
          <c>Dir</c> defines the directory which contains the backup
          copy and the Erlang specific configuration files for
          <c>syslogd</c>, and a named pipe to receive the messages
          from <c>syslogd</c>. Defaults to <c>"/etc"</c>. <c>Conf</c>
          defines the full name of the configuration file for
          <c>syslogd</c>. Default is <c>"/etc/syslog.conf"</c>.</p>
        <p>Results in a OS call to:</p>
        <code type="none"><![CDATA[
<PRIVDIR>/bin/mod_syslog otp Dir Conf
        ]]></code>
        <p>where <c><![CDATA[<PRIVDIR>]]></c> is the <c>priv</c> directory of
          OS_Mon, <c>code:priv_dir(os_mon)</c>.</p>
        <p>Returns <c>ok</c> if this yields the expected result
          <c>"0"</c>, and <c>{error, Res}</c> if it yields anything
          else.</p>
        <note>
          <p>This function requires root privileges to succeed.</p>
        </note>
      </desc>
    </func>
    <func>
      <name since="">disable() -> ok | {error, Res}</name>
      <name since="">disable(Dir, Conf) -> ok | {error, Error}</name>
      <fsummary>Disable the service (Solaris only)</fsummary>
      <type>
        <v>Dir = Conf = Res = string()</v>
      </type>
      <desc>
        <p>Disables the <c>os_sup</c> service. Needed on Solaris only.</p>
        <p>If the configuration parameter <c>os_sup_enable</c> is
          <c>false</c>, this function is called automatically by
          <c>os_sup</c>, using the same arguments as when
          <c>enable/2</c> was called.</p>
        <p>If <c>os_sup_enable</c> is <c>true</c>, this function must
          be called <em>after</em> OS_Mon/<c>os_sup</c> is stopped.
          <c>Dir</c> defines the directory which contains the backup
          copy and the Erlang specific configuration files for
          <c>syslogd</c>, and a named pipe to receive the messages
          from <c>syslogd</c>. Defaults to <c>"/etc"</c>. <c>Conf</c>
          defines the full name of the configuration file for
          <c>syslogd</c>. Default is <c>"/etc/syslog.conf"</c>.</p>
        <p>Results in a OS call to:</p>
        <code type="none"><![CDATA[
<PRIVDIR>/bin/mod_syslog nootp Dir Conf
        ]]></code>
        <p>where <c><![CDATA[<PRIVDIR>]]></c> is the <c>priv</c> directory of
          OS_Mon, <c>code:priv_dir(os_mon)</c>.</p>
        <p>Returns <c>ok</c> if this yields the expected result
          <c>"0"</c>, and <c>{error, Res}</c> if it yields anything
          else.</p>
        <note>
          <p>This function requires root privileges to succeed.</p>
        </note>
      </desc>
    </func>
  </funcs>

  <section>
    <title>See also</title>
    <p><seeerl marker="kernel:error_logger">error_logger(3)</seeerl>,
      <seeapp marker="os_mon_app">os_mon(3)</seeapp></p>
    <p><c>syslogd(1M)</c>, <c>syslog.conf(4)</c> in the Solaris
      documentation.</p>
    <p></p>
  </section>
</erlref>

