Before You Begin

check if your CentOS installation already has swap enabled by typing:

swapon –show

Empty output means that your system does not have swap enabled. Otherwise, swap enabled. Note that you may have multiple swap partitions and/or files.

Creating a Swap Partition

Creating a Swap File

 

First, create a file which will be used as swap space 1GB:

fallocate -l 1G /swapfile

If the fallocate utility is not available

sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576

Ensure that only the root user can read and write the swap file

chmod 600 /swapfile

Next, set up a Linux swap area on the file:

mkswap /swapfile

Run the following command to activate the swap:

swapon /swapfile

Make the change permanent by opening the /etc/fstab file:

vi /etc/fstab

and pasting the following line:

/swapfile swap swap defaults 0 0

Verify that the swap is active

swapon –show

or

free -h

Adjusting the Swappiness Value

Swappiness can have a value between 0 and 100. A low value will make the kernel to try to avoid swapping

cat /proc/sys/vm/swappiness

To set the swappiness value to 10

sysctl vm.swappiness=10

To make this parameter persistent across reboots append the following line to the /etc/sysctl.conf file:

vm.swappiness=10

Removing a Swap File #

Start by deactivating the swap space by typing:

sudo swapoff -v /swapfile

Next, remove the swap file entry /swapfile swap swap defaults 0 0 from the /etc/fstab file.

Finally, delete the actual swapfile file with rm :

sudo rm /swapfile