Resize / remount /dev/shm not working

Question

I've got a linux box dedicated to playing host to an Oracle server installation. It's got 4Gb RAM and by default, 50% (2Gb) has been allocated to /dev/shm. I want to change this to 3Gb, but I am unable to do so.

I've tried:

• Changing the relevant line of /etc/fstab to:

  tmpfs     /dev/shm     tmpfs     size=3g     0 0
  

• Trying to temporarily resize using mount

For whatever reason, it does not appear to resize. Even after a restart (to effect the /etc/fstab change) df -h shows /dev/shm as 2Gb still.

Am I doing something wrong?

Solution

Although I don't think it's causing the problem here, your fstab entry is not 100% complete - you're missing the defaults in the mount options field.

It should read:

tmpfs     /dev/shm     tmpfs     defaults,size=3g     0 0 

That said, you will also need to change an init script for the fstab entry to take effect. See this bug report for more information, but basically you need to change /etc/rc.d/rc.sysinit

from

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

to

mount /dev/shm >/dev/null 2>&1

or add mount -o remount tmpfs to /etc/rc.local.

Note: Based on the age of the question, I'm assuming RHEL 6.x-aged Oracle Linux is the distribution in use.

Comments

[Admin]

Is the OS 32bit?

[Admin]

getconf LONG_BIT informs me that it's 64.

[Admin]

Some distributions hard-code the size of /dev/shm in their startup scripts. Why do you want to reduce the size? It's not as if it consumed memory. The memory used for tmpfs isn't reserved, it's allocated for the files that are actually stored, and it gets swapped out with the rest.

[Admin]

3Gb > 2Gb - I want to increase it. I was investigating performance issues previously and though now I'm quite sure that this is not the issue, I'd still like to increase it (apparently it's definitely not a bad idea). Perhaps it is hard-coded or something though... Hmm.

[Admin]

From the manpage of mount the size= must be given in bytes and only accepts a % suffix. For me a mount -o remount,size=75% /dev/shm worked to increase the space.