ORA-00845: MEMORY_TARGET not supported on this system

Cause : This error comes up because of  Automatic Memory Management (AMM) feature of Oracle 11g R2 seems that shared memory file system (shmfs) is not big enough.

Solution : Increase the size of that file system by issuing the following command.

mount -t tmpfs shmfs -o size=12g /dev/shm

[oracle@OEL64N2 workshops]$ sqlplus /nolog
SQL*Plus: Release 11.2.0.3.0 Production on Sat Aug 15 01:04:51 2015
Copyright (c) 1982, 2011, Oracle.  All rights reserved.
SQL> conn /as sysdba
Connected to an idle instance.
SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system
SQL> exit
Disconnected
[oracle@OEL64N2 workshops]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5             9.9G  3.1G  6.4G  33% /
tmpfs                 1.2G  695M  434M  62% /dev/shm
/dev/sda2             4.0G  139M  3.7G   4% /tmp
/dev/sda1              12G  6.4G  4.9G  57% /u01
[oracle@OEL64N2 workshops]$ mount -t tmpfs shmfs -o size=12g /dev/shm
mount: only root can do that
[oracle@OEL64N2 workshops]$ su root
Password:
[root@OEL64N2 workshops]#
[root@OEL64N2 workshops]#
[root@OEL64N2 workshops]# mount -t tmpfs shmfs -o size=12g /dev/shm
[root@OEL64N2 workshops]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5             9.9G  3.1G  6.4G  33% /
tmpfs                  12G     0   12G   0% /dev/shm
/dev/sda2             4.0G  139M  3.7G   4% /tmp
/dev/sda1              12G  6.4G  4.9G  57% /u01
shmfs                  12G     0   12G   0% /dev/shm
[root@OEL64N2 workshops]# su oracle
[oracle@OEL64N2 workshops]$ sqlplus /nolog
SQL*Plus: Release 11.2.0.3.0 Production on Sat Aug 15 01:08:30 2015
Copyright (c) 1982, 2011, Oracle.  All rights reserved.
SQL> conn /as sysdba
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area  835104768 bytes
Fixed Size                  2232960 bytes
Variable Size             805309824 bytes
Database Buffers           25165824 bytes
Redo Buffers                2396160 bytes
Database mounted.
Database opened.
SQL>