Oracle wont start: ORA-27300, ORA-27301, ORA-27302 (No space left on device)

Ever encountered this error while starting up your Oracle database? At first glance, as the error informs with the line familiar to most administrators "No space left on device", its not actually what you think it is!

Even if you have loads of HDD space and free memory left, this error can happen. Its because you don't have enough semaphores left. A semaphore is a value in a designated place in operating system (or kernel) storage that each process can check and then change (ref).

ORA-27154: post/wait create failed
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: sskgpsemsper

To fix this error, edit your /etc/sysctl.conf file and add/modify the below parameter to the values mentioned below:

kernel.sem = 250 32000 100 128

Now to apply these changes, run the below command:

sysctl -p

Once its done, try starting your database. It should start without the previous error.