ORA-00845: MEMORY_TARGET not supported on this system in Redhat Linux 6 in oracle database 11g/12c

Easy solution for this error is below....

When creating a database with DBCA, you are not able to give more memory to database.

Because of ORA-00845: MEMORY_TARGET not supported on this system

Or

SQL> STARTUP
ORA-00845: MEMORY_TARGET not supported on this system

Cause: 

 Your shared memory which is mapped to /dev/shm directory is less than the size of MEMORY_TARGET or MEMORY_MAX_TARGET. So Oracle can’t able to setup MEMORY_TARGET (AMM- automatic memory management) parameter. Though your shmmax (\etc\sysctl.conf) have enough value.

You can see it with below commands

Root# df –h

Solution:

So we need to change the value of below parameter in /etc/fstab with root user then reboot the server.

tmpfs /dev/shm tmpfs size=7G 0 0

After changing the size=7g (with root user) in /etc/fstab  (was defaults) Automatically memory_target parameters value changed from 0 (zero) to (sga_target + pga_aggregate_target) .

And I am also able to set up memory_target (AMM- automatic memory management)

Cheers.... thanks Halim.