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March 9, 2012

HOW TO : Clear unused swap memory in Linux

Filed under: HOWTO,Linux,Technology — Vinay @ 10:15 am

Inspired by a G+  post by Thomas Weeks .

swap memory is something used by the OS to essentially swap data to and forth if the main memory is not available. It is several times slower than RAM, since it uses hard disk to store the memory. And if you are constantly swapping, your system performance is going to be impacted quite a lot. You should always ensure that¬† your system is not swapping by adding the required RAM and/or stopping your application(s) from using so much memory. At times, because of spike in utilization, the OS might briefly use swap. And when it does, it doesn’t release the memory from swap. So from an analysis prospective, it makes it difficult to check (quickly) if your system is using swap or not. This is similar to errors on an interface in a router. Unless you clear them and monitor, you don’t know when the errors happened.

I was not aware that you could turn off swap devices while the OS is running and then enable them again. So here are the commands to do that in Linux

swapoff -a

This essentially disables swap on all devices configured for swap in /etc/fstab

swapon -a

This does the opposite of the first command. Enabled swap on all devices that have swap configured.

Tom put this into a nice alias by doing the following

alias unswap='sudo swapoff -a && sudo swapon -a'

Thx Tom…

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