ORA-27125: unable to create shared memory segment during startup

Problem

After reboot, unable to startup Oracle 12c database instance (Red Hat Enterprise Server 7.6)

ORA-27125: unable to create shared memory segment
Linux-x86_64 Error: 28: No space left on device
Additional information: 3822
Additional information: 6157238272

Solution

Verify OS kernel.shmall memory setting.

1. Get current value 

cat /proc/sys/kernel/shmall

1677722

This seems to be too high..

2. Determine page size

getconf PAGE_SIZE

4096

3. Calculate recommended value for shmall

shmall = <total size of SGA>/<page size>

In our case, we have 16GB RAM, so, shmall = 16 * 1024 * 1024 * 1024 / 4096 = 4194304

4. Update /etc/sysctl.conf

vi /etc/sysctl.conf

kernel.shmall=4194304

sudo sysctl -p

5. Verify  kernel.shmall again

cat /proc/sys/kernel/shmall

4194304

6. Start Oracle instance

sudo su - oracle

sqlplus / as sysdba

startup;

This of course leads to another error..

References

https://support.oracle.com/knowledge/Oracle%20Database%20Products/301830_1.html

http://www.nazmulhuda.info/ora-27102-out-of-memory-linux-x86_64-error-28-no-space-left-on-device

https://it.toolbox.com/blogs/surachartopun/shared-memory-startup-database-ora-27102-out-of-memory-linux-x86-64-error-28-no-space-left-on-device-102409

https://jameshuangsj.wordpress.com/2018/06/07/ora-27125-unable-to-create-shared-memory-segment-linux-x86_64-error-28-no-space-left-on-device/