How to fix "Could not find or load main class com.install4j.runtime.launcher.UnixLauncher" error when starting the nexus service - redhat

Question

Operating system: Red Hat Entreprise Linux server release 7.7
nexus version: 3.18.1-01
When renewing the SSL certificate of Nexus on the server, I first replaced the old certificate under /opt/nexus/etc/ssl with the new one.
I put a new keystore with the new certificate and the same password as before with the same name in the same place and then ran /opt/nexus/bin/nexus restart.
Before the service was running and the URL was reachable, but since then I get the following error:
Could not find or load main class
com.install4j.runtime.launcher.UnixLauncher.
And the command journalctl -u nexus gives the following error:
Failed to start nexus service.
Failed at step EXEC spawning /var/nexus/bin/nexus: Permission denied.
i tried a lot of things i found on the internet to fix this but unfortunately without success.
put the nexus user in the nexus.rc file
run_as_user="nexus"
In the beginning it was like this:
#run_as_user=""
That means, the nexus server is run with root and I tried to run it with the user nexus. Unfortunately this did not work.
I also tried the following:
changed the permission and owner for the "/opt/nexus" and "/var/nexus" folders (tested with root and nexus too).
moved the file .install4j to /opt/nexus/
at the end I wanted to test again with the old certificate and renamed the new one und the new key. I thought it was because of the new certificate.... But I still get the same error:
Could not find or load main class
com.install4j.runtime.launcher.UnixLauncher
Something is wrong since I stopped and restarted the nexus service but i don't know what exactly.
Can you help me please? I would be very grateful.

Answer 1

Check the ownership of the PID file:
https://help.sonatype.com/display/NXRM3/Run+as+a+Service#RunasaService-PIDFile