When you start up your database oracle 11g R2 shows the error MEMORY_TARGET not supported on this system" because of tried to use Automatic Memory Management.



SQL> STARTUP MOUNT



ORA-00845: MEMORY_TARGET not supported on this system

Solution:

The memory space not enough for start oracle, We need to increase tmpfs space,

The commands to check file system space


SQL>!df -h



SQL> exit
# df -h


Filesystem      Size  Used Avail Use% Mounted on

/dev/xvda1       99G  4.1G   90G   5% /

tmpfs           976M     0  976M   0% /dev/shm

The below command to help enlarge the tmpfs space  upto 5GB, your shared memory filesystem to avoid the error above.
 
# mount -o remount,size=5G /dev/shm

This file system to be set parmanently update in fstab,
 
# vim /etc/fstab
tmpfs   /dev/shm        tmpfs   defaults,size=5G        0       0
# mount -a

# df -h


Filesystem      Size  Used Avail Use% Mounted on

/dev/xvda1       99G  4.1G   90G   5% /

tmpfs           5.0G  466M  4.6G  10% /dev/shm
# sqlplus sys/password  as sysdba


SQL> STARTUP MOUNT



ORACLE instance started.



Total System Global Area  814227456 bytes

Fixed Size            2230896 bytes

Variable Size          541066640 bytes

Database Buffers      268435456 bytes

Redo Buffers            2494464 bytes

Database mounted.

or

Another option is unmount and mount with 5000M space,
 
# umount tmpfs

# mount -t tmpfs shmfs -o size=5000m /dev/shm