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erldaemon

erldaemon is a small helper program to create well-behaved UNIX daemons with the Erlang emulator. In particular erldaemon provides the following capabilities which are hard to achieve with plain Erlang:

  • Detach from console only after the daemon was initialized successfully
  • Return proper exit code if initialization fails
  • Maintain a PID-file
  • Orderly shutdown when receiving SIGTERM
  • Log rotation upon receiving SIGHUP

Building

To build erldaemon you will need rebar and obviously Erlang.

$ rebar compile

As erldaemon is an OTP application you have to put it in the Erlang code path. The erldaemon executable can be found in the priv directory after compilation.

Usage

erldaemon is pretty much self contained and doesn't need any specific changes to your Erlang application(s). Typically you will just start Erlang through erldaemon which redirects stdout to some log file and creates the PID file:

$ cd erldaemon
$ ./priv/erldaemon -l /var/log/myapp.log -p /var/run/myapp.pid -- erl +Bd -noinput \
  -pa "$PWD/ebin" -s myapp -s erldaemon
  • Erlang must be started with +Bd -noinput flags. This disables the break handler (erldaemon takes care of this) and disables the shell because Erlang will have no stdin when run through erldaemon.
  • Your application(s) should be started as permanent application, that is with application:start(myapp, permanent). This makes sure that the Erlang emulator dies if the application cannot be started successfully.
  • erldaemon must be started as the last application. The erldaemon application makes the detach from the console and listens to SIGTERM shutdown requests.

Use erldaemon -h to get an overview about the available command line options.