WARNING: You are trying to use the MEMORY_TARGET feature.

WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least 6442450944 bytes. /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that MEMORY_TARGET can work as expected. Current available is 4067700736 and used is 127700992 bytes. Ensure that the mount point is /dev/shm for this directory.
memory_target needs larger /dev/shm.

You can also face the following error.

ORA-00845: MEMORY_TARGET not supported on this system

Cause: This warning show cause of when we are trying to use Automatic Memory Management feature in Unix/Linux system the tmpfs should be big enough to accommodate the MEMORY_TARGET and MEMORY_MAX_TARGET values.

Solution : Increase the tmpfs size.

1.
cp /etc/rc.d/rc.sysinit /etc/rc.d/rc.sysinit.orig

vi /etc/rc.d/rc.sysinit

edite this existing line and add new one from the file of /etc/rc.d/rc.sysinit

        #mount -f /dev/shm >/dev/null 2>&1
        mount /dev/shm >/dev/null 2>&1

2.
cp /etc/rc.local /etc/rc.local.orig
vi /etc/rc.local

Add the following line in the end of /etc/rc.local file.

mount -o remount tmpfs

3.
cp /etc/fstab /etc/fstab.orig

vi /etc/fstab

edite this existing line and add new one from the file of /etc/fstab

#tmpfs                   /dev/shm                tmpfs   defaults        0 0
tmpfs   /dev/shm        tmpfs   size=8g 0 0

4. Now check your system.

[root@sbdbdr01 ~]# df -k /dev/shm
Filesystem           1K-blocks      Used Available Use% Mounted on
tmpfs                  8388608    381216   8007392   5% /dev/shm

Log
-------------


[root@sbdbdr01 ~]# cp /etc/rc.d/rc.sysinit /etc/rc.d/rc.sysinit.orig
[root@sbdbdr01 ~]# vi /etc/rc.d/rc.sysinit
[root@sbdbdr01 ~]# cat /etc/rc.d/rc.sysinit
        mount -f /
        mount -f /proc >/dev/null 2>&1
        mount -f /sys >/dev/null 2>&1
        mount -f /dev/pts >/dev/null 2>&1
        #mount -f /dev/shm >/dev/null 2>&1
mount /dev/shm >/dev/null 2>&1
        mount -f /proc/bus/usb >/dev/null 2>&1
[root@sbdbdr01 ~]# cp /etc/rc.local /etc/rc.local.orig
[root@sbdbdr01 ~]# cat /etc/rc.local
#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local
[root@sbdbdr01 ~]# vi /etc/rc.local
[root@sbdbdr01 ~]# cat /etc/rc.local
#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local
mount -o remount tmpfs
[root@sbdbdr01 ~]# cp /etc/fstab /etc/fstab.orig
[root@sbdbdr01 ~]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Mon May  9 16:34:50 2016
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=3f2c16d3-6add-4a4d-89a2-824bd6090239 /                       ext4    defaults        1 1
UUID=4af12c05-0f8a-4082-bbeb-55d9e77931c3 /tmp                    ext4    defaults        1 2
UUID=2469b10b-3673-4b9b-8fcb-7d1465db42e9 swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/sdb1 /u01                   ext4    defaults        1 2
[root@sbdbdr01 ~]#
[root@sbdbdr01 ~]# vi /etc/fstab
[root@sbdbdr01 ~]# cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Mon May  9 16:34:50 2016
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=3f2c16d3-6add-4a4d-89a2-824bd6090239 /                       ext4    defaults        1 1
UUID=4af12c05-0f8a-4082-bbeb-55d9e77931c3 /tmp                    ext4    defaults        1 2
UUID=2469b10b-3673-4b9b-8fcb-7d1465db42e9 swap                    swap    defaults        0 0
#tmpfs                   /dev/shm                tmpfs   defaults        0 0
tmpfs   /dev/shm        tmpfs   size=8g 0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/sdb1 /u01                   ext4    defaults        1 2
[root@sbdbdr01 ~]# mount -o remount tmpfs
[root@sbdbdr01 ~]#
[root@sbdbdr01 ~]# df -k /dev/shm
Filesystem           1K-blocks      Used Available Use% Mounted on
tmpfs                  8388608    381216   8007392   5% /dev/shm
[root@sbdbdr01 ~]#
[root@sbdbdr01 ~]# reboot

Broadcast message from root@sbdbdr01
        (/dev/pts/0) at 12:33 ...

The system is going down for reboot NOW!
[root@sbdbdr01 ~]#