heart

heart(3)                   ERLANG MODULE DEFINITION                   heart(3)



MODULE
       heart - Heartbeat Monitoring of an Erlang Runtime System.

DESCRIPTION
       The heart module 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 (default is 60 seconds) from the last one, 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.

       This module is started by the init module during system start-up. The
       -heart command line flag determines if the heart module should start .

       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 erl -heart is started or can be passed on
       the command line like this: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).


EXPORTS
       start() -> {ok, Pid} | ignore | {error, What}

              Types  Pid = pid()
                     What = void()

              Starts the heart program. This function returns ignore if the
              -heart command line flag is not supplied.

       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.

              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.

AUTHORS
       Magnus Fröberg - support@erlang.ericsson.se
       Kenneth Lundin - support@erlang.ericsson.se



Ericsson Utvecklings AB          kernel  2.7.2                        heart(3)