ORA-00845: MEMORY_TARGET not supported on this system

Issue:

While creating a database 12c using dbca the database creation GUI gives error message in a pop up window,
ORA-00845: MEMORY_TARGET not supported on this system from where you can ignore the error message and perform the solution mentioned below and retry the failed steps during installation.

The similar scenario also occur whenever you try to start your database then startup shows error message like below.

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


Cause:

1)If the shared memory which is mapped to /dev/shm directory is less than the size of MEMORY_TARGET or MEMORY_MAX_TARGET.

2)If the shared memory is not mapped to /dev/shm directory.

Solution:

Make sure /dev/shm is properly mounted. You can see it by,
#df -h or #df -k command.

[root@testing shm]# df -kh
Filesystem            Size  Used Avail Use% Mounted on
shmfs                 5.0G  815M  4.3G  16% /dev/shm

We see here for /dev/shm we have assigned 5G memory. Now if you set MEMORY_TARGET more than 5G then above ORA-845 will arise. For example if you have MEMORY_TARGET or MEMORY_MAX_TARGET set to 10G then you can mount shared memory to 11g like below.

From root user, fire the following command:

mount -t tmpfs shmfs -o size=11g /dev/shm

In order to make the settings persistence so that it will affect after restarting machine add an entry in /etc/fstab similar to the following:

shmfs /dev/shm tmpfs size=11g 0