FIX- ORA-00845: MEMORY_TARGET not supported on this system:

 FIX- ORA-00845: MEMORY_TARGET not supported on this system:
 
$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
                       50G  506M   47G   2% /
tmpfs                 7.8G  3.8G  4.1G  49% /dev/shm
/dev/sda1             485M   58M  402M  13% /boot

 [oracle@exilant ~]$ su root
Password:
[root@exilant oracle]# mount -t tmpfs shmfs -o size=12g /dev/shm
[root@exilant oracle]# vi /etc/fstab add this line

shmfs                   /dev/shm                tmpfs   size=12g      0 0

root@exilant oracle]# su oracle
[oracle@exilant ~]$ sqlplus / as sysdba

SQL> startup;
ORACLE instance started.

Follow this link for the refrence:
 http://www.krenger.ch/blog/ora-00845-memory_target-not-supported-on-this-system/

http://www.oracle-base.com/articles/11g/automatic-memory-management-11gr1.php