Add support for new relx directive that provides start/stop shell script hooks

New 'extended_start_script_hooks' directive that allows the
developer to define six different hook shell scripts to be invoked
at pre/post start/stop/install upgrade phases.
Besides these custom defined scripts, other types of builtin
scripts are also available, these offer pre-packaged functionality
that can be used directly, they are:
  pid - writes the beam pid to a configurable file location
          (/var/run/<rel_name>.pid by default).
  wait_for_vm_start - waits for the vm to start (ie. when it responds to pings)
  wait_for_process - waits for a configurable name
                                to appear in the erlang process registry
The hook scripts are invoked with the 'source' command, therefore
they have access to all the variables in the start script.

1 files changed, 12 insertions, 0 deletions

diff --git a/priv/templates/builtin_hook_pid b/priv/templates/builtin_hook_pid
new file mode 100644
index 0000000..0151631
--- /dev/null
+++ b/priv/templates/builtin_hook_pid
@@ -0,0 +1,12 @@
+#!/bin/bash
+
+# loop until the VM starts responding to pings
+while ! $(relx_nodetool "ping">/dev/null)
+do
+    sleep 1
+done
+
+# get the beam pid and write it to the file passed as
+# argument
+PID="$(relx_get_pid)"
+echo $PID > $1