Wednesday, November 26, 2008

Clear Swap Space in Linux

There have been times where it has been necessary for me to clear out the swap space on a Linux system. In order to do this, you must first make sure that you have enough free memory to hold what is being used by swap.
I usually do this in a few steps. You do need to be root to do this. First I want to see what is currently being used.
free

Then I run the actual commands that empty the swap:
swapoff -a && swapon -a

Then I check what is being used after doing this.
free

I have these three steps in a script and then I just run the script, but, the commands could easily be run from the command line.

13 comments:

Волошин Руслан said...

Thanx it help for me

Anonymous said...

Thanks. I had puzzling situation with 4G RAM mostly free but a whole G of swap in use.
Your command line cleared swap although I'm still a bit puzzled.
top shows Swap: 2031608k total, 0k used, 2031608k free, 2031472k cached

What is that cached swap?

colymoore@gmail.com

Anonymous said...

Yes! Did exactly what I was wanting to do.

Anonymous said...

yup...really good advice...only that I don't think you really need the exact amount of free RAM as the amount of occupied swap...

I had 700 MB of used RAM out of 2 GB and 1.3 GB of swap. after using your commands I have 1.3 GB of RAM used and no swap :P

Thank you anyway

Duber said...

Thankkkkkkks, just what I was looking for.

Reshen said...

Thanks Dude. Short and sweet. Did exactly what I needed. Much Appreciated!

Weird World News said...

Rather use:

sync; echo 3 > /proc/sys/vm/drop_caches

It is better to sync before messing with cache

Anonymous said...

Thanks I was exactly looking for this.

Burhan

Nasimuddin Ansari said...

Below will decrease number incached colum and increased number in fee Mem colum. No effect for swap usages.

sync; echo 3 > /proc/sys/vm/drop_caches

[root@uksysops004 ~]# free -to
total used free shared buffers cached
Mem: 4046272 3924208 122064 0 334268 967444
Swap: 8191992 1499496 6692496
Total: 12238264 5423704 6814560
# sync; echo 3 > /proc/sys/vm/drop_caches
# free -to
total used free shared buffers cached
Mem: 4046272 2458000 1588272 0 404 59940
Swap: 8191992 1499496 6692496
Total: 12238264 3957496 8280768
#

Unknown said...
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Unknown said...

The best super all in one clear cache, buffers and swap file in one go:

sync && sudo /sbin/sysctl vm.drop_caches=3 && sudo swapoff -a && sudo swapon -a

You might need to alter the permissions on the sysctl or vm.drop_caches file, or run the following command under su/root:

sync && /sbin/sysctl vm.drop_caches=3 && swapoff -a && swapon -a

Works flawless, every time :)

-Jamie M.

Curt- said...

Also, /proc/sys/vm/swappiness by default is 60, with 100 being aggressive swapping, 0 being "use swap only when actually running out of RAM"

Nice quick article. Agreed about sync first, though. Just in case.