Your message dated Thu, 7 May 2026 13:58:54 +0300 with message-id <caoq2pxen89pkjnrxc7wm1-i9z6+z-sxd_hudzc2b1bsgvjz...@mail.gmail.com> and subject line Re: Bug#1135795: [Pkg-erlang-devel] Bug#1135795: epmd.socket fails to bind to 127.0.0.1:4369 with “Address already in use” even when nothing is listening has caused the Debian Bug report #1135795, regarding epmd.socket fails to bind to 127.0.0.1:4369 with “Address already in use” even when nothing is listening to be marked as done.
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--- Begin Message ---Package: erlang-base Version: 1:27.3.4.1+dfsg-1+deb13u1 Sure — here’s a concise bug report draft you can send to the Debian maintainer. I'm reporting an issue with the Debian epmd systemd socket/service setup. On my system, epmd initially appears to be listening on all interfaces: ss -tulpn | grep epmd tcp LISTEN 0 4096 *:4369 *:* users:(("epmd",pid=2368130,fd=3),("systemd",pid=1,fd=199)) I tried to restrict epmd to localhost by creating a systemd socket override: [Socket] ListenStream=127.0.0.1:4369 After that, I ran: systemctl daemon-reload systemctl restart epmd.socket epmd.service At that point, `pmd.socket failed to start with: epmd.socket: Failed to create listening socket (127.0.0.1:4369): Address already in use This was surprising because no process appeared to be holding port 4369 at that point. I checked with `ss`, and nothing was listening on 4369. However, after removing the socket override entirely, running: systemctl daemon-reload systemctl restart epmd.socket epmd.service epmd started successfully again. So the problem seems to be that overriding epmd.socket with "ListenStream=127.0.0.1:4369" causes a bind failure even when the port is not in use. It looks like either: - the packaged systemd socket setup does not support this override cleanly, - the socket unit and service interaction is not behaving as expected, - or there is some hidden conflict/state left behind by the existing epmd setup. System details: - Debian 13 - epmd auto-installed by ejabberd (apt install ejabberd) Expected behavior: - epmd.socket should bind to 127.0.0.1:4369 successfully when the port is free. Actual behavior: - epmd.socket fails with "Address already in use"
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--- Begin Message ---Hi! On Thu, May 7, 2026 at 1:15 AM <[email protected]> wrote: > > > It's reasonable if you don't use distributed Erlang. > > Not sure I understand. When I ran "apt install ejabberd", it > auto-installed Erlang via apt. > As far as I know, ejabberd is a distributed XPP server, even if there is a single node, ejabberd uses distributed Erlang. > > > I can reproduce this, as far as I investigated, it is caused by the option > > BindIPv6Only=both > > in the socket file. When systemd binds to IPv6 address, it also listens to > > IPv4 > > packets, which makes address already in use. > > I was finally able to listen on "127.0.0.1" only, because opening 4369 > publicly is asking for trouble[1]. I guess you should file a bugreport for Erlang developers for that. As for now I don't know about any exploitable vulnerability in epmd. > > # ss -tulpn|grep epmd > tcp LISTEN 0 4096 127.0.0.1:4369 0.0.0.0:* > users:(("epmd",pid=2370007,fd=3),("systemd",pid=1,fd=199)) > > To do this, I had to: > > 1. Run: systemctl edit epmd.socket > 2. Add 2 lines line this: > > ### Editing /etc/systemd/system/epmd.socket.d/override.conf > ### Anything between here and the comment below will become the contents > of the drop-in file > > [Socket] > ListenStream= > ListenStream=127.0.0.1:4369 You've found another way of teaching epmd.socket to listen only on 12.7.0.0.1, good. > > Anyway, I don't think that's a bug in epmd.socket. It works as intended. > > I think there is a bug because when I edit like below, epmd failed to > restart. > > [Socket] > ListenStream=127.0.0.1:4369 I don't think that I can account for all possible ways the users chose to override the default socket settings. This particular way fails, but there are others, they are documented in /usr/share/doc/erlang-base/README.Debian. > > I need to add "ListenStream=" - unsure if this is a correct fix but some > people mentioned this on other forums. No, you don't. Please, read the readme in /usr/share/doc/erlang-base/README.Debian, it explains how to make the epmd socket listen only on the lo interface (localhost). As for now, I'm closing this bugreport. Cheers! -- Sergei Golovan
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