Increase temporary space in /dev/shm on OEL 6.x for Oracle SGA mapping

How to  Increase size of tmpfs file system ( OEL 6.3)  for Oracle SGA mapping ?

tmpfs filesystem keeps the entire filesystem (with all it’s files) in virtual memory. All data is stored in memory,  which means the data is temporary and will be lost after a reboot. If you unmount the filesystem, all data in there is gone. Typically it is mounted to /dev/shm .

  • The default size of the filesystem is half of the installed memory in the system.

Temporary increase tmpfs filesystem

To increase the size, do the following: 
Modify /etc/fstab line to look something like this:
 tmpfs      /dev/shm        tmpfs   defaults,size=16g        0 0 

Remount tmpfs and verify :
# mount -o remount tmpfs 
Verify :
# df -h
 Filesystem            Size  Used Avail Use% Mounted on
    tmpfs                  16G  232M   16G   2% /dev/shm


Make  temporay changes permanent even after a reboot

  • After a  reboot the tmpfs filesystem is back to half of the system’s memory !

Strange, isn’t it ?
According to the following WA can be used to get this changed permanently.

Change  /etc/rc.d/rc.sysinit from
   mount -f /dev/shm >/dev/null 2>&1
   mount /dev/shm >/dev/null 2>&1

or add to /etc/rc.local  
# remount tmpfs to read the size parameter
mount -o remount tmpfs


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