Swap is a space on a that is used when the amount of physical RAM memory is full. When a system runs out of RAM, inactive pages are moved from the RAM to the swap space.

Swap space can take the form of either a dedicated swap partition or a swap . In most cases when running Linux on a a swap partition is not present so our only option is to create a swap file.

Follow these steps to add 1GB of swap to your . If you want to add 2GB instead of 1 GB, replace 1G with 2G.

  1. Create a file which will be used for swap.
    sudo fallocate -l 1G /swapfile

    If faillocate is not installed or if you get an error message saying fallocate failed: Operation not supported then you can use the following to create the swap file:

    sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
  2. Set the correct permissions.

    Only the user should be able to write and read the swap file. To set the right permissions type:

    sudo chmod 600 /swapfile
  3. Set up a Linux swap area.

    Use the mkswap utility to set up the file as Linux swap area:

    sudo mkswap /swapfile
  4. Enable the swap.

    Activate the swap file with the following command:

    sudo swapon /swapfile

    To make the change permanent open the /etc/ file and append the following line:

    /etc/fstab
    /swapfile swap swap defaults 0 0
  5. Verify the swap status.

    To verify that the swap is active we can use either the swapon or the free command as shown below:

    sudo swapon --show
    NAME      TYPE  SIZE   USED PRIO
    /swapfile file 1024M 507.4M   -1
    sudo free -h
                  total        used        free      shared  buff/   available
    Mem:           488M        158M         83M        2.3M        246M        217M
    Swap:          1.0G        506M        517M

Swappiness is a Linux property that defines how often the system will use the swap space. Swappiness can have a value between 0 and 100. A low value will make the to try to avoid swapping whenever possible while a higher value will make the to use the swap space more aggressively.

The default swappiness value is 60. You can check the current swappiness value by typing the following command:

cat /proc/sys//swappiness
60

While the swappiness value of 60 is OK for Desktops, for production servers you may need to set a lower value.

For example, to set the swappiness value to 10, type:

sudo sysctl vm.swappiness=10

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

/etc/sysctl.conf
vm.swappiness=10

The optimal swappiness value depends on your system workload and how the memory is being used. You should adjust this parameter in small increments to find an optimal value.

If for any reason you want to deactivate and remove the swap file, follow these steps:

  1. First, deactivate the swap using the following command:
    sudo swapoff -v /swapfile
  2. Remove the swap file entry /swapfile swap swap defaults 0 0 from the /etc/fstabfile.
  3. Finally delete the actual swapfile file:
    sudo rm /swapfile
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