Why does my Mosquitto broker fail to start on boot, but works when started manually?

Question

I have a UDOO x86 running Ubuntu 18.04.5 LTS, with Mosquitto v2. This setup has worked as expected until a recent Ubuntu update.

Now, Mosquitto fails to start on boot. In the Mosquitto log file I see that it correctly finds my config file, but then fails with:

Opening ipv4 listen socket on port 1883.
Error: Cannot assign requested address

It then immediately attempts to restart four more times in rapid succession before (apparently) giving up.

Strangely, if I start Mosquitto manually (using sudo systemctl start mosquitto) immediately after boot, the broker starts without error and works properly (both listeners, see below).

My mosquitto.conf:

log_type all
allow_anonymous true
listener 1883 10.11.12.222  # <-- local IP address of my machine
listener 1883 localhost

I've determined that the error is caused by the line with the IP address. If I use only localhost, or if I just use listener 1883 (which I think binds to all adapters?), mosquitto starts and works correctly.

The computer has two network adapters -- an Ethernet adapter statically assigned to 10.11.12.222, and a wireless adapter on a different subnet (using DHCP) connected to the interwebs. I'd like limit my listener to the Ethernet adapter only (and localhost), hence the desire to specify the IP address.

I've tried turning off allow_anonymous and adding a password file -- this doesn't change the behavior.

Answer 1

I had same problem on aarch64. Based on Mark G comment I changed service configuration to

[Unit]
After=network-online.target
Wants=network-online.target