Fails to start with ERL_EPMD_ADDRESS=127.0.0.1

[paulmenzel]

Setting the environment variable for the epmd address to localhost ERL_EPMD_ADDRESS=127.0.0.1 in the systemd service unit

Environment=ETURNAL_ETC_PREFIX=/project/eturnal ERL_EPMD_ADDRESS=127.0.0.1

eturnal fails to start with the error below.

eturnalctl[91982]: Protocol 'inet_tcp': register/listen error: econnrefused

[paulmenzel]

epmd is not a separate service and should be started by eturnal.

[weiss]

Sounds like epmd fails to start with an ERL_EPMD_ADDRESS on your system. One possible reason would be that IPv6 is disabled in a way that doesn't allow binding to ::1 (which epmd tries to do if you specify an IPv4 listen address, which is the reason we no longer do that by default).

If this is not the issue: Does journalctl -u eturnal show additional output? Do you get any output when stopping eturnal and then calling ERL_EPMD_ADDRESS=127.0.0.1 epmd -d manually?

[paulmenzel]

Sounds like epmd fails to start with an ERL_EPMD_ADDRESS on your system. One possible reason would be that IPv6 is disabled in a way that doesn't allow binding to ::1 (which epmd tries to do if you specify an IPv4 listen address, which is the reason we no longer do that by default).

Indeed, IPv6 is disabled in our environment.

$ sysctl net.ipv6.conf.all.disable_ipv6
net.ipv6.conf.all.disable_ipv6 = 1

[weiss]

net.ipv6.conf.all.disable_ipv6 = 1

Yes, this is the setup that lets epmd fail: Binding to INADDR6_ANY works, binding to INADDR6_LOOPBACK doesn't. On our IPv4-only servers, we disable the IPv6 stack altogether by adding ipv6.disable_ipv6=1 to the kernel command line. That way, epmd won't attempt to bind to ::1. (See also this posting, for example.)

So there's nothing we can do about this; if anything, the problem could be reported against Erlang/OTP.

[paulmenzel]

So there's nothing we can do about this; if anything, the problem could be reported against Erlang/OTP.

erlang/otp#4820

[weiss]

Seems this will be fixed in future Erlang/OTP releases.