When trying to patch OMS 12.1.0.5 in a VirtualBox environment with latest OMS PSU, I came across a strange problem which took quite a while to solve. The opatchauto apply and also -analyze commands failed every time with this error after several minutes of hanging:

opatchauto failed with error code 231

Manual connect to WLS console with relevant protocol/host/port/username/password was working fine. Then I realized that there was an issue with the entropy pool on the VirtualBox VM.

I followed this Note to resolve the isse:

E1: OS: Linux Servers Hang or Have Delays on Any JAVA Process Affecting Performance (Doc ID 1525645.1)

After implementing rngd, the patching worked successfully without any hangs.