Assalamu’alaikum Wr. Wb.
Oracle database uses /dev/shm for its memory target allocation. So, if space of /dev/shm is running out to allocate memory_target, Oracle will failed to startup and shown ORA-00845: MEMORY_TARGET not supported on this system. By default, CentOS 7.4.1708 as my Oracle DB platform allocate only 1.4GB /dev/shm. So I have to increase /dev/shm permanently for bigger memory_target. Sure, it is different way from RHEL/CentOS/OEL 6.
It is easy, I create shell script to remount the /dev/shm, give it executable permission, and put it into crontab so that remount for everystartup. You can also run mount -o remount,size=2g /dev/shm on the fly. But I didn’t it, after all done I reboot the OS to make sure my shell script and crontab running well 🙂
Now check the /dev/shm and … my /dev/shm is 2GB.
Good luck 🙂