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Linux 2.6 - man page for heart (linux section 3erl)

heart(3erl)			     Erlang Module Definition			      heart(3erl)

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	automati-
       cally:

       % 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 con-
       figure  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).

       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 environ-
	      ment variable HEART_COMMAND to reboot.

	      Limitations: The length of the Cmd command string must be less  than  2047  charac-
	      ters.

       clear_cmd() -> ok

	      Clears  the temporary boot command. If the system terminates, the normal HEART_COM-
	      MAND 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 2.14.3 			      heart(3erl)


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