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<!DOCTYPE comref SYSTEM "comref.dtd">

<comref>
  <header>
    <copyright>
      <year>1998</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>erlsrv</title>
    <prepared>Patrik Nyblom</prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date>98-04-29</date>
    <rev></rev>
    <file>erlsrv.xml</file>
  </header>
  <com>erlsrv</com>
  <comsummary>Run the Erlang emulator as a service on Windows NT&reg;</comsummary>
  <description>
    <p>This utility is specific to Windows NT/2000/XP&reg; (and subsequent versions of Windows) It allows Erlang
      emulators to run as services on the Windows system, allowing embedded
      systems to start without any user needing to log in. The
      emulator started in this way can be manipulated through the
      Windows&reg; services applet in a manner similar to other
      services.</p>
    <p>Note that erlsrv is not a general service utility for Windows, but designed for embedded Erlang systems.</p> 
    <p>As well as being the actual service, erlsrv also provides a
      command line interface for registering, changing, starting and
      stopping services.</p>
    <p>To manipulate services, the logged in user should have
      Administrator privileges on the machine. The Erlang machine
      itself is (default) run as the local administrator. This can be
      changed with the Services applet in Windows &reg;.</p>
    <p>The processes created by the service can, as opposed to normal
      services, be "killed" with the task manager. Killing a emulator
      that is started by a service will trigger the "OnFail" action
      specified for that service, which may be a reboot.</p>
    <p>The following parameters may be specified for each Erlang
      service:</p>
    <list type="bulleted">
      <item>
        <p><c><![CDATA[StopAction]]></c>: This tells <c><![CDATA[erlsrv]]></c> how to stop
          the Erlang emulator. Default is to kill it (Win32
          TerminateProcess), but this action can specify any Erlang
          shell command that will be executed in the emulator to make
          it stop. The emulator is expected to stop within 30 seconds
          after the command is issued in the shell. If the emulator is
          not stopped, it will report a running state to the service
          manager.</p>
      </item>
      <item>
        <p><c><![CDATA[OnFail]]></c>: This can be either of <c><![CDATA[reboot]]></c>,
          <c><![CDATA[restart]]></c>, <c><![CDATA[restart_always]]></c> or <c><![CDATA[ignore]]></c> (the
          default). In case of <c><![CDATA[reboot]]></c>, the NT system is
          rebooted whenever the emulator stops (a more simple form of
          watchdog), this could be useful for less critical systems,
          otherwise use the heart functionality to accomplish
          this. The restart value makes the Erlang emulator be
          restarted (with whatever parameters are registered for the
          service at the occasion) when it stops. If the emulator
          stops again within 10 seconds, it is not restarted to avoid
          an infinite loop which could completely hang the NT
          system. <c><![CDATA[restart_always]]></c> is similar to restart, but
          does not try to detect cyclic restarts, it is expected that
          some other mechanism is present to avoid the problem.  The
          default (ignore) just reports the service as stopped to the
          service manager whenever it fails, it has to be manually
          restarted.</p>
        <p>On a system where release handling is
          used, this should always be set to <c><![CDATA[ignore]]></c>. Use
          <c><![CDATA[heart]]></c> to restart the service on failure instead.</p>
      </item>
      <item>
        <p><c><![CDATA[Machine]]></c>: The location of the Erlang
          emulator. The default is the <c><![CDATA[erl.exe]]></c> located in the
          same directory as erlsrv.exe. Do not specify <c><![CDATA[werl.exe]]></c>
          as this emulator, it will not work.</p>
        <p>If the system
          uses release handling, this should be set to a program
          similar to <c><![CDATA[start_erl.exe]]></c>.</p>
      </item>
      <item>
        <p><c><![CDATA[Env]]></c>: Specifies an <em>additional</em> environment
          for the emulator. The environment variables specified
          here are added to the system wide environment block that is
          normally present when a service starts up. Variables present
          in both the system wide environment and in the service
          environment specification will be set to the value specified
          in the service.</p>
      </item>
      <item>
        <p><c><![CDATA[WorkDir]]></c>: The working directory for the Erlang
          emulator, has to be on a local drive (there are no network
          drives mounted when a service starts). Default working
          directory for services is <c><![CDATA[%SystemDrive%%SystemPath%]]></c>.
          Debug log files will be placed in this directory.</p>
      </item>
      <item>
        <p><c><![CDATA[Priority]]></c>: The process priority of the emulator,
          this can be one of <c><![CDATA[realtime]]></c>, <c><![CDATA[high]]></c>, <c><![CDATA[low]]></c>
          or <c><![CDATA[default]]></c> (the default). Real-time priority is not
          recommended, the machine will possibly be inaccessible to
          interactive users. High priority could be used if two Erlang
          nodes should reside on one dedicated system and one should
          have precedence over the other. Low process priority may be
          used if interactive performance should not be affected by
          the emulator process.</p>
      </item>
      <item>
        <p><c><![CDATA[SName or Name]]></c>: Specifies the short or long
          node-name of the Erlang emulator. The Erlang services are
          always distributed, default is to use the service name as
          (short) node-name.</p>
      </item>
      <item>
        <p><c><![CDATA[DebugType]]></c>: Can be one of <c><![CDATA[none]]></c> (default),
          <c><![CDATA[new]]></c>, <c><![CDATA[reuse]]></c> or <c><![CDATA[console]]></c>.
          Specifies that output from the Erlang shell should be
          sent to a "debug log". The log file is named
          &lt;servicename&gt;<c><![CDATA[.debug]]></c> or
          &lt;servicename&gt;<c><![CDATA[.debug.]]></c>&lt;N&gt;, where &lt;N&gt; is
          an integer between 1 and 99. The log-file is placed in the
          working directory of the service (as specified in WorkDir). The
          <c><![CDATA[reuse]]></c> option always reuses the same log file
          (&lt;servicename&gt;<c><![CDATA[.debug]]></c>) and the <c><![CDATA[new]]></c> option
          uses a separate log file for every invocation of the service
          (&lt;servicename&gt;<c><![CDATA[.debug.]]></c>&lt;N&gt;). The <c><![CDATA[console]]></c>
          option opens an interactive Windows&reg; console window for
          the Erlang shell of the service. The <c><![CDATA[console]]></c> option 
          automatically
          disables the <c><![CDATA[StopAction]]></c> and a service started with an
          interactive console window will not survive logouts, 
          <c><![CDATA[OnFail]]></c> actions do not work with debug-consoles either.
          If no <c><![CDATA[DebugType]]></c> is specified (<c><![CDATA[none]]></c>), the
          output of the Erlang shell is discarded.</p>
        <p>The <c><![CDATA[console]]></c><c><![CDATA[DebugType]]></c> is <em>not in any way</em>
          intended for production. It is <em>only</em> a convenient way to
          debug Erlang services during development. The <c><![CDATA[new]]></c> and
          <c><![CDATA[reuse]]></c> options might seem convenient to have in a
          production system, but one has to take into account that the
          logs will grow indefinitely during the systems lifetime and
          there is no way, short of restarting the service, to
          truncate those logs. In short, the <c><![CDATA[DebugType]]></c> is
          intended for debugging only. Logs during production are
          better produced with the standard Erlang logging
          facilities.</p>
      </item>
      <item>
        <p><c><![CDATA[Args]]></c>: Additional arguments passed to the
          emulator startup program <c><![CDATA[erl.exe]]></c> (or
          <c><![CDATA[start_erl.exe]]></c>).  Arguments that cannot be specified
          here are <c><![CDATA[-noinput]]></c> (StopActions would not work),
          <c><![CDATA[-name]]></c> and <c><![CDATA[-sname]]></c> (they are specified in any
          way. The most common use is for specifying cookies and flags
          to be passed to init:boot() (<c><![CDATA[-s]]></c>).</p>
      </item>
      <item>
        <p><c><![CDATA[InternalServiceName]]></c>: Specifies the Windows&reg; internal service name (not the display name, which is the one <c>erlsrv</c> uses to identify the service).</p>
	<p>This internal name can not be changed, it is fixed even if the service is renamed. <c>Erlsrv</c> generates a unique internal name when a service is created, it is recommended to keep to the defaut if release-handling is to be used for the application.</p>
	<p>The internal service name can be seen in the Windows&reg; service manager if viewing <c>Properties</c> for an erlang service.</p>
      </item>
      <item>
        <p><c><![CDATA[Comment]]></c>: A textual comment describing the service. Not mandatory, but shows up as the service description in the Windows&reg; service manager.</p>
      </item>
    </list>
    <p>      <marker id="001"></marker>
 The naming of the service in a system that
      uses release handling has to follow the convention
      <em>NodeName</em>_<em>Release</em>, where <em>NodeName</em> is
      the first part of the Erlang nodename (up to, but not including
      the "@") and <em>Release</em> is the current release of the
      application.</p>
  </description>
  <funcs>
    <func>
      <name>erlsrv {set | add} &lt;service-name> [&lt;service options>]</name>
      <fsummary>Add or modify an Erlang service</fsummary>
      <desc>
        <p>The set and add commands adds or modifies a Erlang service
          respectively.  The simplest form of an add command would be
          completely without options in which case all default values
          (described above) apply. The service name is mandatory.</p>
        <p>Every option can be given without parameters, in which case
          the default value is applied. Values to the options are
          supplied <em>only</em> when the default should not be used
          (i.e. <c><![CDATA[erlsrv set myservice -prio -arg]]></c> sets the
          default priority and removes all arguments).</p>
        <p>The following service options are currently available:</p>
        <taglist>
          <tag>-st[opaction] [&lt;erlang shell command&gt;]</tag>
          <item>Defines the StopAction, the command given to the Erlang
           shell when the service is stopped. Default is none.</item>
          <tag>-on[fail] [{reboot | restart | restart_always}]</tag>
          <item>Specifies the action to take when the Erlang emulator
           stops unexpectedly. Default is to ignore.</item>
          <tag>-m[achine] [&lt;erl-command&gt;]</tag>
          <item>The complete path to the Erlang emulator, never use the
           werl program for this. Default is the <c><![CDATA[erl.exe]]></c> in the
           same directory as <c><![CDATA[erlsrv.exe]]></c>. When release handling
           is used, this should be set to a program similar to
          <c><![CDATA[start_erl.exe]]></c>.</item>
          <tag>-e[nv] [&lt;variable&gt;[=&lt;value&gt;]] ...</tag>
          <item>Edits the environment block for the service. Every
           environment variable specified will add to the system
           environment block. If a variable specified here has the same
           name as a system wide environment variable, the specified
           value overrides the system wide.  Environment variables are
           added to this list by specifying
           &lt;variable&gt;=&lt;value&gt; and deleted from the list by
           specifying &lt;variable&gt; alone. The environment block is
           automatically sorted. Any number of <c><![CDATA[-env]]></c> options can
           be specified in one command. Default is to use the system
           environment block unmodified (except for two additions, see
          <seealso marker="#002">below</seealso>).</item>
          <tag>-w[orkdir] [&lt;directory&gt;]</tag>
          <item>The initial working directory of the Erlang
           emulator. Default is the system directory.</item>
          <tag>-p[riority] [{low|high|realtime}]</tag>
          <item>The priority of the Erlang emulator. The default is the
           Windows&reg; default priority.</item>
          <tag>{-sn[ame] | -n[ame]} [&lt;node-name&gt;]</tag>
          <item>The node-name of the Erlang machine, distribution is
           mandatory. Default is <c><![CDATA[-sname <service name>]]></c>.
          </item>
          <tag>-d[ebugtype] [{new|reuse|console}]</tag>
          <item>Specifies where shell output should be sent,
           default is that shell output is discarded. 
           To be used only for debugging.</item>
          <tag>-ar[gs] [&lt;limited erl arguments&gt;]</tag>
          <item>Additional arguments to the Erlang emulator, avoid
          <c><![CDATA[-noinput]]></c>, <c><![CDATA[-noshell]]></c> and
          <c><![CDATA[-sname]]></c>/<c><![CDATA[-name]]></c>. Default is no additional
           arguments. Remember that the services cookie file is not
           necessarily the same as the interactive users. The service
           runs as the local administrator. All arguments should be given
           together in one string, use double quotes (") to give an
           argument string containing spaces and use quoted quotes (\")
           to give an quote within the argument string if
           necessary.</item>
	   <tag>-i[nternalservicename] [&lt;internal name&gt;]</tag>
           <item><em>Only</em> allowed for <c>add</c>. Specifies a
           Windows&reg; internal service name for the service, which by
           default is set to something unique (prefixed with the
           original service name) by erlsrv when adding a new
           service. Specifying this is a purely cosmethic action and is
           <em>not</em> recommended if release handling is to be
           performed. The internal service name cannot be changed once
           the service is created. The internal name is <em>not</em> to 
	   be confused with the ordinary service name, which is the name 
	   used to identify a service to erlsrv.</item>
	   <tag>-c[omment] [&lt;short description&gt;]</tag>
           <item>Specifies a textual comment describing the
           service. This comment will show upp as the service description
           in the Windows&reg; service manager.</item>
        </taglist>
      </desc>
    </func>
    <func>
      <name>erlsrv {start | start_disabled | stop | disable | enable} &lt;service-name></name>
      <fsummary>Manipulate the current service status.</fsummary>
      <desc>
        <p>These commands are only added for convenience, the normal
          way to manipulate the state of a service is through the
          control panels services applet. The <c><![CDATA[start]]></c> and
          <c><![CDATA[stop]]></c> commands communicates
          with the service manager for stopping and starting a
          service. The commands wait until the service is actually
          stopped or started. When disabling a service, it is not
          stopped, the disabled state will not take effect until the
          service actually is stopped. Enabling a service sets it in
          automatic mode, that is started at boot. This command cannot
          set the service to manual.  </p>

	<p>The <c>start_disabled</c> command operates on a service
	regardless of if it's enabled/disabled or started/stopped.  It
	does this by first enabling it (regardless of if it's enabled
	or not), then starting it (if it's not already started) and
	then disabling it. The result will be a disabled but started
	service, regardless of its earlier state. This is useful for
	starting services temporarily during a release upgrade. The
	difference between using <c>start_disabled</c> and the
	sequence <c>enable</c>, <c>start</c> and <c>disable</c> is
	that all other <c>erlsrv</c> commands are locked out during
	the sequence of operations in <c>start_disable</c>, making the
	operation atomic from an <c>erlsrv</c> user's point of
	view.</p>

      </desc>
    </func>
    <func>
      <name>erlsrv remove &lt;service-name&gt;</name>
      <fsummary>Remove the service.</fsummary>
      <desc>
        <p>This command removes the service completely with all its registered
          options. It will be stopped before it is removed.</p>
      </desc>
    </func>
    <func>
      <name>erlsrv list [&lt;service-name&gt;]</name>
      <fsummary>List all Erlang services or all options for one service.</fsummary>
      <desc>
        <p>If no service name is supplied, a brief listing of all Erlang services
          is presented. If a service-name is supplied, all options for that
          service are presented.</p>
      </desc>
    </func>
    <func>
      <name>erlsrv help</name>
      <fsummary>Display a brief help text</fsummary>
    </func>
  </funcs>

  <section>
    <title>ENVIRONMENT</title>
    <p>      <marker id="002"></marker>
The environment of an Erlang machine started
      as a service will contain two special variables,
      <c><![CDATA[ERLSRV_SERVICE_NAME]]></c>, which is the name of the service that
      started the machine and <c><![CDATA[ERLSRV_EXECUTABLE]]></c> which is the
      full path to the <c><![CDATA[erlsrv.exe]]></c> that can be used to manipulate
      the service. This will come in handy when defining a heart command for
      your service. A command file for restarting a service will
      simply look like this:</p>
    <code type="none"><![CDATA[
@echo off
%ERLSRV_EXECUTABLE% stop %ERLSRV_SERVICE_NAME%
%ERLSRV_EXECUTABLE% start %ERLSRV_SERVICE_NAME%    ]]></code>
    <p>This command file is then set as heart command.</p>
    <p>The environment variables can also be used to detect that we
      are running as a service and make port programs react correctly
      to the control events generated on logout (see below).</p>
  </section>

  <section>
    <title>PORT PROGRAMS</title>
    <p>When a program runs in
      the service context, it has to handle the control events that is
      sent to every program in the system when the interactive user
      logs off. This is done in different ways for programs running in
      the console subsystem and programs running as window
      applications. An application which runs in the console subsystem
      (normal for port programs) uses the win32 function
      <c><![CDATA[SetConsoleCtrlHandler]]></c> to register a control handler
      that returns TRUE in answer to the <c><![CDATA[CTRL_LOGOFF_EVENT]]></c>
      and <c><![CDATA[CTRL_SHUTDOWN_EVENT]]></c> events. Other applications
      just forward <c><![CDATA[WM_ENDSESSION]]></c> and
      <c><![CDATA[WM_QUERYENDSESSION]]></c> to the default window procedure.
      Here is a brief example in C of how to set the console control
      handler:</p>
    <code type="none"><![CDATA[
#include <windows.h>
/* 
** A Console control handler that ignores the log off events,
** and lets the default handler take care of other events.
*/   
BOOL WINAPI service_aware_handler(DWORD ctrl){
    if(ctrl == CTRL_LOGOFF_EVENT)
        return TRUE;
    if(ctrl == CTRL_SHUTDOWN_EVENT)
        return TRUE;
    return FALSE;
}

void initialize_handler(void){
    char buffer[2];
    /* 
     * We assume we are running as a service if this  
     * environment variable is defined
     */
    if(GetEnvironmentVariable("ERLSRV_SERVICE_NAME",buffer,
                              (DWORD) 2)){
        /*
        ** Actually set the control handler
        */
        SetConsoleCtrlHandler(&service_aware_handler, TRUE);
    }
}    ]]></code>
  </section>

  <section>
    <title>NOTES</title>
    <p>Even though the options are described in a Unix-like format, the case of
      the options or commands is not relevant, and the "/" character for options
      can be used as well as the "-" character. </p>
    <p>Note that the program resides in the emulators
      <c><![CDATA[bin]]></c>-directory, not in the <c><![CDATA[bin]]></c>-directory directly under
      the Erlang root. The reasons for this are the subtle problem of
      upgrading the emulator on a running system, where a new version of
      the runtime system should not need to overwrite existing (and probably
      used) executables.</p>
    <p>To easily manipulate the Erlang services, put
      the <c><![CDATA[<erlang_root>\erts-<version>\bin]]></c> directory in
      the path instead of <c><![CDATA[<erlang_root>\bin]]></c>. The erlsrv program
      can be found from inside Erlang by using the
      <c><![CDATA[os:find_executable/1]]></c> Erlang function.</p>
    <p>For release handling to work, use <c><![CDATA[start_erl]]></c> as the Erlang
      machine. It is also worth mentioning again that the name of the 
      service is significant (see <seealso marker="#001">above</seealso>).</p>
  </section>

  <section>
    <title>SEE ALSO</title>
    <p>start_erl(1), release_handler(3)</p>
  </section>
</comref>

