ORA-27154: post/wait create failed
This error is due to the failure of obtaining the OS semaphore (semaphore can be understood as memory lock) during the startup process, and the process needs to obtain the semaphore before requesting memory for use.
Generally, the processes parameter in oracle is set to processes*2+15 during installation is safer.

Usually the error ORA-27154: post/wait create failed is accompanied by the following errors.
ORA-27300: OS system dependent operation:semget failed with status: 28
ORA-27301: OS failure message: No space left on device
ORA-27302: failure occurred at: sskgpcreates
These errors are caused by the fact that the processed is too large and the amount of signals to be acquired is not enough.

Check the current settings
[oracle@ebsse oracle]$ cat /proc/sys/kernel/sem
250 32000 100 128

The 4 data items correspond to SEMMSL SEMMNS SEMOPM SEMMNI
Instead of explaining the meaning of the data, let's just talk about the modification.

Change the value of sem to: 5010 641280 5010 128

For automatic application at boot time, add to /etc/sysctl.conf:
kernel.sem =5010 641280 5010 128

sysctl -p