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man pages section 1: User Commands

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Updated: Wednesday, February 9, 2022

erlsrv (1)


erlsrv - Run the Erlang emulator as a service on Windows


Please see following description for synopsis


erlsrv(1)                        User Commands                       erlsrv(1)

       erlsrv - Run the Erlang emulator as a service on Windows

       This  utility  is specific to Windows NT/2000/XP (and later 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 on. The emulator started in this way can be manipulated through the
       Windows services applet in a manner similar to other services.

       Notice  that  erlsrv  is not a general service utility for Windows, but
       designed for embedded Erlang systems.

       erlsrv also provides a command-line interface for  registering,  chang-
       ing, starting, and stopping services.

       To  manipulate  services,  the  logged on user is to 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.

       The processes created by the service can, as  opposed  to  normal  ser-
       vices,  be  "killed" with the task manager. Killing an emulator that is
       started by a service triggers the "OnFail" action  specified  for  that
       service, which can be a reboot.

       The following parameters can be specified for each Erlang service:

           Tells erlsrv 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
           reports a running state to the service manager.

           Can be one of the following:

             The Windows system is rebooted whenever  the  emulator  stops  (a
             more simple form of watchdog). This can be useful for less criti-
             cal systems, otherwise use the heart functionality to  accomplish

             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 hang the Windows system.

             Similar to restart, but does not try to detect  cyclic  restarts;
             it  is expected that some other mechanism is present to avoid the

           ignore (the default):
             Reports the service as stopped to the service manager whenever it
             fails; it must be manually restarted.

           On  a  system  where release handling is used, this is always to be
           set to ignore. Use heart to restart the service on failure instead.

           The location of the Erlang emulator. The  default  is  the  erl.exe
           located  in  the  same  directory  as  erlsrv.exe.  Do  not specify
           werl.exe as this emulator, it will not work.

           If the system uses release handling, this is to be set to a program
           similar to start_erl.exe.

           Specifies  an  extra  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

           The working directory for the Erlang emulator. Must be on  a  local
           drive  (no  network  drives  are  mounted  when  a service starts).
           Default working directory  for  services  is  %SystemDrive%%System-
           Path%. Debug log files will be placed in this directory.

           The process priority of the emulator. Can be one of the following:

             Not  recommended, as the machine will possibly be inaccessible to
             interactive users.

             Can be used if two Erlang nodes are to reside  on  one  dedicated
             system and one is to have precedence over the other.

             Can  be  used if interactive performance is not to be affected by
             the emulator process.

           default (the default>:

         SName or Name:
           Specifies the short or long node name of the Erlang  emulator.  The
           Erlang  services are always distributed. Default is to use the ser-
           vice name as (short) nodename.

           Specifies that output from the Erlang shell is  to  be  sent  to  a
           "debug log". The log file is named <servicename>.debug or <service-
           name>.debug.<N>, where <N> is an integer from 1 through 99. The log
           file  is  placed in the working directory of the service (as speci-
           fied in WorkDir).

           Can be one of the following:

             Uses a separate log file for  every  invocation  of  the  service

             Reuses the same log file (<servicename>.debug).

             Opens  an interactive Windows console window for the Erlang shell
             of the service. Automatically disables the StopAction. A  service
             started  with  an  interactive  console  window  does not survive
             logouts. OnFail actions do not work with debug consoles either.

           none (the default):
             The output of the Erlang shell is discarded.

         The console option is not intended for production. It is only a  con-
         venient way to debug Erlang services during development.

         The  new and reuse options might seem convenient in a production sys-
         tem, but consider that the logs grow indefinitely during  the  system
         lifetime and cannot be truncated, except if the service is restarted.

         In  short,  the DebugType is intended for debugging only. Logs during
         production are better  produced  with  the  standard  Erlang  logging

           Passes  extra arguments to the emulator startup program erl.exe (or
           start_erl.exe). Arguments that cannot be specified here are  -noin-
           put (StopActions would not work), -name, and -sname (they are spec-
           ified in any way). The most common use is  for  specifying  cookies
           and flags to be passed to init:boot() (-s).

           Specifies  the Windows-internal service name (not the display name,
           which is the one erlsrv uses to identify the service).

           This internal name cannot be changed, it is fixed even if the  ser-
           vice  is  renamed.  erlsrv  generates a unique internal name when a
           service is created. It is recommended to keep  to  the  default  if
           release handling is to be used for the application.

           The  internal  service name can be seen in the Windows service man-
           ager if viewing Properties for an Erlang service.

           A textual comment describing the service. Not mandatory, but  shows
           up as the service description in the Windows service manager.

       The  naming  of the service in a system that uses release handling must
       follow the convention NodeName_Release, where  NodeName  is  the  first
       part  of  the  Erlang  node name (up to, but not including the "@") and
       Release is the current release of the application.

       erlsrv {set | add} <service-name> [<service options>]

              The set and add commands modifies or  adds  an  Erlang  service,
              respectively. The simplest form of an add command is without any
              options in which  case  all  default  values  (described  above)
              apply. The service name is mandatory.

              Every  option  can  be specified without parameters, the default
              value is then applied. Values to the options are  supplied  only
              when  the  default  is  not  to be used. For example, erlsrv set
              myservice -prio -arg sets the default priority and  removes  all

              Service options:

                -st[opaction] [<erlang shell command>]:
                  Defines  the  StopAction,  the  command  given to the Erlang
                  shell when the service is stopped. Default is none.

                -on[fail] [{reboot | restart | restart_always}]:
                  The action to take when the Erlang emulator stops  unexpect-
                  edly. Default is to ignore.

                -m[achine] [<erl-command>]:
                  The complete path to the Erlang emulator. Never use the werl
                  program for this. Defaults to the erl.exe in the same direc-
                  tory  as  erlsrv.exe. When release handling is used, this is
                  to be set to a program similar to start_erl.exe.

                -e[nv] [<variable>[=<value>]] ...:
                  Edits the environment block for the service. Every  environ-
                  ment  variable  specified is added to the system environment
                  block. If a variable specified here has the same name  as  a
                  system-wide  environment variable, the specified value over-
                  rides the system-wide. Environment variables  are  added  to
                  this  list by specifying <variable>=<value> and deleted from
                  the list by specifying  <variable>  alone.  The  environment
                  block  is  automatically  sorted. Any number of -env options
                  can be specified in one command. Default is to use the  sys-
                  tem  environment block unmodified (except for two additions,
                  see section Environment below).

                -w[orkdir] [<directory>]:
                  The  initial  working  directory  of  the  Erlang  emulator.
                  Defaults to the system directory.

                -p[riority] [{low|high|realtime}]:
                  The  priority of the Erlang emulator. Default to the Windows
                  default priority.

                {-sn[ame] | -n[ame]} [<node-name>]:
                  The node name of the Erlang machine. Distribution is  manda-
                  tory. Defaults to -sname <service name>.

                -d[ebugtype] [{new|reuse|console}]:
                  Specifies  where shell output is to be sent. Default is that
                  shell output is discarded. To be used only for debugging.

                -ar[gs] [<limited erl arguments>]:
                  Extra arguments to  the  Erlang  emulator.  Avoid  -noinput,
                  -noshell,  and  -sname/-name. Default is no extra arguments.
                  Remember that the services cookie file  is  not  necessarily
                  the  same  as the interactive users. The service runs as the
                  local administrator. Specify all arguments together  in  one
                  string,  use double quotes (") to specify an argument string
                  containing spaces, and use quoted quotes (\") to  specify  a
                  quote within the argument string if necessary.

                -i[nternalservicename] [<internal name>]:
                  Only  allowed  for add. Specifies a Windows-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  cos-
                  methic  action and is not recommended if release handling is
                  to be performed. The internal service name cannot be changed
                  once  the service is created. The internal name is not to be
                  confused with the ordinary service name, which is  the  name
                  used to identify a service to erlsrv.

                -c[omment] [<short description>]:
                  Specifies  a  textual  comment  describing the service. This
                  comment shows up as the service description in  the  Windows
                  service manager.

       erlsrv  {start  |  start_disabled  | stop | disable | enable} <service-

              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 start and stop commands communicates with the  service  man-
              ager  for  starting  and  stopping  a service. The commands wait
              until the service is started or stopped. When disabling  a  ser-
              vice, it is not stopped, the disabled state does not take effect
              until the service is stopped. Enabling  a  service  sets  it  in
              automatic  mode,  which  is started at boot. This command cannot
              set the service to manual.

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

       erlsrv remove <service-name>

              Removes the service completely with all its registered  options.
              It is stopped before it is removed.

       erlsrv list [<service-name>]

              If  no  service name is specified, a brief listing of all Erlang
              services is presented.  If  a  service  name  is  supplied,  all
              options for that service are presented.

       erlsrv help

              Displays a brief help text.

       The  environment of an Erlang machine started as a service contains two
       special variables:

           The name of the service that started the machine.

           The full path to the erlsrv.exe, which can be  used  to  manipulate
           the  service. This comes in handy when defining a heart command for
           your service.

       A command file for restarting a service looks as follows:

       @echo off

       This command file is then set as heart command.

       The environment variables can also be used to detect that we  are  run-
       ning as a service and make port programs react correctly to the control
       events generated on logout (see the next section).

       When a program runs in the service context, it must handle the  control
       events  that  are sent to every program in the system when the interac-
       tive user logs off. This is done in different ways for programs running
       in  the  console subsystem and programs running as window applications.
       An application running in the console subsystem (normal for  port  pro-
       grams) uses the win32 function SetConsoleCtrlHandler to register a con-
       trol handler that returns true in answer to the  CTRL_LOGOFF_EVENT  and
       CTRL_SHUTDOWN_EVENT  events. Other applications only forward WM_ENDSES-
       SION and WM_QUERYENDSESSION to the default window procedure.

       A brief example in C of how to set the console control handler:

       #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.
                                     (DWORD) 2)){
               ** Actually set the control handler
               SetConsoleCtrlHandler(&service_aware_handler, TRUE);

       Although the options are described in a Unix-like format, the  case  of
       the options or commands is not relevant, and both character "/" and "-"
       can be used for options.

       Notice that the program resides in the emulator's bin directory, not in
       the  bin 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.

       To    manipulate    the    Erlang    services    easily,    put     the
       <erlang_root>\erts-<version>\bin  directory  in  the  path  instead  of
       <erlang_root>\bin. The erlsrv program can be found from  inside  Erlang
       by using the os:find_executable/1 Erlang function.

       For  release  handling to work, use start_erl as the Erlang machine. As
       stated above, the service name is significant.

       start_erl(1), release_handler(3)

Ericsson AB                        erts 12.0                         erlsrv(1)