ORA-00845: MEMORY_TARGET not supported on this system



Login as root, umount /dev/shm and mount it using -o size=4096m.

$ umount /dev/shm
$ mount -o size=4096m /dev/shm

And can make it persistent by modifying /etc/fstab

tmpfs   /dev/shm        tempfs  defaults        0 0
to
tmpfs   /dev/shm        tempfs  size=4096m      0 0