Turn off swap

Not every Linux server I maintain needs to have a swap partition and to start swapping. For instance, the MySQL servers all have more than enough RAM on board to do their work. Yet, when a swap partition is enabled Linux starts swapping, which may degrade MySQL database and system performance…

Bash script to turn off Linux swap

An unwanted Linux swap partition can be the result of an automated and unattended Linux installation. Of course you can fiddle with the Linux kernel swapiness settings, located in /proc/sys/vm/swapiness and configurable in /etc/sysctl.conf, but one can turn off the swap completely too.

Here’s a tiny bash script to disable Linux’ swap – for which we use the swapoff command – and to comment out the swap partition in /etc/fstab:

#!/bin/bash
# swapoff -a to disable swapping
swapoff -a

# sed to comment the swap partition in /etc/fstab
sed -i.bak -r 's/(.+ swap .+)/#\1/' /etc/fstab

Save this as turn_swap_off.sh and execute as root:

sh /root/turn_swap_off.sh

A backup of the /etc/fstab file is made just to be sure and to stay on the safe side.

Disable swappiness kernel parameter

Swappiness is a property for the Linux kernel that changes the balance between swapping out runtime memory, as opposed to dropping pages from the system page cache. Swappiness can be set to values between 0 and 100, inclusive. A low value means the kernel will try to avoid swapping as much as possible where a higher value instead will make the kernel aggressively try to use swap space.

You manage swappiness with sysctl, either to get its current value or to set a new swappiness value. You can also use cat to verify the current setting. For example:

# get current swappiness value using cat
$ cat /proc/sys/vm/swappiness60

# get current swappiness value using sysctl
$ sudo sysctl vm.swappiness
[sudo] password for user:
vm.swappiness = 60

# set a new swappiness value to 10
$ sudo sysctl vm.swappiness=10

By default, the vm.swappiness value on most Linux computers is set to 60. The higher the number, the more aggressively the VM swaps data to disk. You can change this level to a different setting either temporarily or indefinitely.

You can also edit the /etc/sysctl.conf configuration file. Open the file /etc/sysctl.conf with your text editor and change the value of the following entry vm.swappiness to your suitable value (add the entry if it does not exist).

$ sudo vi /etc/sysctl.conf
$ grep swappiness /etc/sysctl.confvm.swappiness=10