Ramdisk ubuntu 10.04

Question

I'm using Ubuntu 10.04(64bit) for my desktop.
The machine has a 5GB RAM.

I want to use RAM disk(1G or 2G) but I don't know how can I do this.

Is there any opensource product of RAM disk?

Answer 1

The technology is built into the kernel, you don't need any extra tools. In fact, you already have a few RAM disks (which you shouldn't use, they're reserved for the system), which you can see by doing

grep -w tmpfs /proc/mounts

To set up a 2GB RAM disk mounted on /ramdisk, add the following line to /etc/fstab:

ramdisk  /ramdisk  tmpfs  mode=1777,size=2g

Then mount the disk with the command mount /ramdisk (this will be done automatically when you reboot).

The indicated size is a maximum, the disk only uses as much memory as the files that are on it.

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You can change /tmp to be a RAM disk. In the /etc/fstab line above, put /tmp rather than /ramdisk, then reboot.

The first time you reboot after changing /tmp to be a RAM disk, the files that were in /tmp will be hidden. That's harmless, except that they're wasting a little disk space. You can clean them up (after you've rebooted with /tmp on the RAM disk) by doing

mount --bind / /mnt
rm -r /mnt/tmp/* /mnt/tmp/.*
umount /mnt

The mount --bind command makes /mnt a duplicate view of your root filesystem; but while the RAM disk now obscures /tmp on the root view, nothing is obscuring /mnt/tmp.

ADDED: You can switch /tmp to a RAM disk without rebooting, it's just a little more complicated. Add the line to /etc/fstab as above, then run the following commands:

mkdir /tmp.old
mount --bind /tmp /tmp.old
mount /tmp
cd /tmp
ln -s /tmp.old/* /tmp/.* .

Then delete /tmp.old after your next reboot.

The reason you can't just move files from /tmp.old to /tmp is that some critical programs have files open in /tmp, for example /tmp/.X11-unix/X0 which the X server listens on and every GUI program opens when it starts. Moving a file to a different filesystem means copying it and deleting the old one, so you would end up with the X server still listening on /tmp.old/.X11-unix/X0 but X clients contacting /tmp/.X11-unix/X0 in vain. On a server, you might get away with a move if you're careful.