NAME

       heart - Heartbeat Monitoring of an Erlang Runtime System

DESCRIPTION

       This  modules contains the interface to the heart process. heart sends periodic heartbeats to an external
       port program, which is also named heart. The purpose of the heart port  program  is  to  check  that  the
       Erlang  runtime  system  it  is  supervising  is  still running. If the port program has not received any
       heartbeats within HEART_BEAT_TIMEOUT seconds (default is 60 seconds), the system can be  rebooted.  Also,
       if the system is equipped with a hardware watchdog timer and is running Solaris, the watchdog can be used
       to supervise the entire system.

       An Erlang runtime system to be monitored by a heart program, should be started with the command line flag
       -heart (see also erl(1)). The heart process is then started automatically:

       % erl -heart ...

       If  the  system should be rebooted because of missing heart-beats, or a terminated Erlang runtime system,
       the environment variable HEART_COMMAND has to be set before the system is started. If  this  variable  is
       not set, a warning text will be printed but the system will not reboot. However, if the hardware watchdog
       is used, it will trigger a reboot HEART_BEAT_BOOT_DELAY seconds later nevertheless (default is 60).

       To  reboot  on  the  WINDOWS platform HEART_COMMAND can be set to heart -shutdown (included in the Erlang
       delivery) or of course to any other suitable program which can activate a reboot.

       The hardware watchdog will not be started under Solaris if the environment variable HW_WD_DISABLE is set.

       The HEART_BEAT_TIMEOUT and HEART_BEAT_BOOT_DELAY environment variables can be used to configure the heart
       timeouts, they can be set in the operating system shell before Erlang is started or be specified  at  the
       command line:

       % erl -heart -env HEART_BEAT_TIMEOUT 30 ...

       The value (in seconds) must be in the range 10 < X <= 65535.

       It  should be noted that if the system clock is adjusted with more than HEART_BEAT_TIMEOUT seconds, heart
       will timeout and try to reboot the system. This can happen, for example, if the system clock is  adjusted
       automatically by use of NTP (Network Time Protocol).

       If   a   crash   occurs,   an  erl_crash.dump  will  not  be  written  unless  the  environment  variable
       ERL_CRASH_DUMP_SECONDS is set.

       % erl -heart -env ERL_CRASH_DUMP_SECONDS 10 ...

       Furthermore, ERL_CRASH_DUMP_SECONDS has the following behaviour on heart:

         ERL_CRASH_DUMP_SECONDS=0:
           Suppresses the writing a crash dump file entirely, thus rebooting  the  runtime  system  immediately.
           This is the same as not setting the environment variable.

         ERL_CRASH_DUMP_SECONDS=-1:
           Setting  the  environment  variable  to a negative value will not reboot the runtime system until the
           crash dump file has been completly written.

         ERL_CRASH_DUMP_SECONDS=S:
           Heart will wait for S seconds to let the crash dump file be  written.  After  S  seconds  heart  will
           reboot the runtime system regardless of the crash dump file has been written or not.

       In the following descriptions, all function fails with reason badarg if heart is not started.

EXPORTS

       set_cmd(Cmd) -> ok | {error, {bad_cmd, Cmd}}

              Types:

                 Cmd = string()

              Sets  a  temporary  reboot  command.  This  command  is used if a HEART_COMMAND other than the one
              specified with the environment variable should be used in order to  reboot  the  system.  The  new
              Erlang  runtime  system  will  (if  it  misbehaves)  use the environment variable HEART_COMMAND to
              reboot.

              Limitations: The length of the Cmd command string must be less than 2047 characters.

       clear_cmd() -> ok

              Clears the temporary boot command. If the system terminates, the normal HEART_COMMAND is  used  to
              reboot.

       get_cmd() -> {ok, Cmd}

              Types:

                 Cmd = string()

              Get the temporary reboot command. If the command is cleared, the empty string will be returned.

Ericsson AB                                       kernel 2.16.4                                      heart(3erl)