Linux Swap

Table of Contents

1. General idea
2. Changing swappiness value temporarily
3. Set swappiness value permanently
4. Using swap file (instead of swap partition)

General idea

Swapping is a technique where data in Random Access Memory (RAM) is written to a special location on your hard disk—either a swap partition or a swap file—to free up RAM. Based on Linux documentation:

"This control is used to define how aggressive (sic) the kernel will swap memory pages.
Higher values will increase aggressiveness, lower values decrease the amount of swap.
A value of 0 instructs the kernel not to initiate swap until the amount of free and
file-backed pages is less than the high water mark in a zone.

The default value is 60."

Changing swappiness value temporarily

sudo sysctl vm.swappiness={value}

Set swappiness value permanently

Open /etc/sysctl.conf file and add this line.

vm.swappiness={value}

Using swap file (instead of swap partition)

1. Create a swapfile

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

   /swapfile is the path and name of the swap file. You can change this to something else.
   The number for count=1048576 equals 1GB. To increase size, multiply that number by 4 if 4GB swap is desired.

2. Set the swap file permission to 600

    sudo chmod 600 /swapfile
   

3. Format the newly created file as swap

    sudo mkswap /swapfile
   

4. Enable the newly created swap file

    sudo swapon /swapfile
   

   To verify if the new swap file is in use, run swapon -s

5. Add entry to /etc/fstab

    /swapfile none swap sw 0 0