Systemd Unit Fails at Boot, but Succeeds when Started from the Console

Sunday, 30 April 2023

This unit 
   $ cat /etc/systemd/system/noip-duc.service  
   [Unit]
   Description=No-IP Dynamic Update Client
   After=network.target auditd.service

   [Service]
   EnvironmentFile=/etc/sysconfig/noip-duc
   ExecStart=/usr/local/bin/noip-duc
   Restart=on-failure
   Type=simple

   [Install]
   WantedBy=multi-user.target
always fails at boot time with the message status=2/INVALIDARGUMENT

Here is an extract from the system log (a fuller extract is attached):
   Mar 18 07:57:56 OaklandWeather.localdomain systemd[1]: Started noip-
   duc.service - No-IP Dynamic Update Client.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Main process exited, code=exited, status=2/INVALIDARGUMENT
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Failed with result 'exit-code'.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Scheduled restart job, restart counter is at 1.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: Stopped noip-
   duc.service - No-IP Dynamic Update Client.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: Started noip-
   duc.service - No-IP Dynamic Update Client.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Main process exited, code=exited, status=2/INVALIDARGUMENT
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Failed with result 'exit-code'.
   Mar 18 07:57:58 OaklandWeather.localdomain systemd[1]: noip-duc.service:
   Scheduled restart job, restart counter is at 2.

However if the unit is started from the console after the boot process
is complete:
   $ systemctrl start noip-duc.service
it succeeds.
How can I find out what the argument is with which systemd is invoking
noip-duc, so I can understand why it is invalid at boot time but valid
when the unit is started afterwards from the console? I would simply
recompile it to output this, but noip-duc is written in the rust
programming language, which I to lazy to learn for this one application.

-- 
Sincerely Jonathan Ryshpan <jonrysh(a)pacbell.net&gt;

 We dance around in a ring and suppose
 But the secret sits in the center and knows.
 - Robert Frost