SQL> startup nomount;
ORA-00845: MEMORY_TARGET not supported on this system
This error comes up because you tried to use the Automatic Memory Management (AMM) feature of Oracle 11g R2. Well done, but it seems that your shared memory filesystem (shmfs) is not big enough. So let’s look at the steps necessary to enlarge your shared memory filesystem to avoid the error above.
mount -t tmpfs shmfs -o size= /dev/shm