Don't send unasked for systemd notifications

Suppose we have some erlang system that uses systemd unit with
Type=notify - so this should send startup confirmation itself. But if
systemd-enabled epmd will be started as a first step of that system
startup, empd startup confirmation will be misinterpeted by systemd. And
our erlang service will be considered 'ready' to early. Also this will
interefere with systemd MAINPID detection: systemd will be monitoring
`epmd` process instead of `beam` one.

For example, rabbitmq works around this issue by starting epmd using
separate short-lived beam process, with NOTIFY_SOCKET environment
variable reset - only in this way we could be sure that epmd will not
interfere with rabbit startup sequence.

This patch disables indiscriminate confirmation sending, and does it
only when it was explicitly asked to do so.

1 files changed, 5 insertions, 3 deletions

diff --git a/erts/epmd/src/epmd_srv.c b/erts/epmd/src/epmd_srv.c
index e1bac99ef9..59d59ad0f7 100644
--- a/erts/epmd/src/epmd_srv.c
+++ b/erts/epmd/src/epmd_srv.c
@@ -452,9 +452,11 @@ void run(EpmdVars *g)
   num_sockets = bound;
 #ifdef HAVE_SYSTEMD_DAEMON
     }
-    sd_notifyf(0, "READY=1\n"
-                  "STATUS=Processing port mapping requests...\n"
-                  "MAINPID=%lu", (unsigned long) getpid());
+    if (g->is_systemd) {
+      sd_notifyf(0, "READY=1\n"
+                    "STATUS=Processing port mapping requests...\n"
+                    "MAINPID=%lu", (unsigned long) getpid());
+    }
 #endif /* HAVE_SYSTEMD_DAEMON */
 
   dbg_tty_printf(g,2,"entering the main select() loop");