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swap

Introduction​

This cheat sheet provides a quick reference for common concepts and commands related to swap space management in Linux.

Swap Space Concepts​

What Is Swap Space?​

Swap space, also known as a swap file or swap partition, is a part of the storage that is used as virtual memory when the physical RAM (Random Access Memory) is fully utilized. It allows the system to move inactive data and programs out of RAM to free up space for currently running processes.

Checking Swap Space​

Verify the amount of swap space in use and available.

  • Display swap space information:

    swapon --show

  • Check system-wide swap usage:

    free -h

Creating Swap Space​

You can create a new swap file or a swap partition if needed.

  • Create a swap file (e.g., 2GB):

    sudo fallocate -l 2G /swapfile
    sudo chmod 600 /swapfile
    sudo mkswap /swapfile
    sudo swapon /swapfile

  • Create a swap partition using fdisk or gparted and activate it:

    sudo mkswap /dev/sdXN
    sudo swapon /dev/sdXN

Disabling Swap​

If necessary, you can disable swap space.

  • Disable swap space:
    sudo swapoff -v /swapfile   # For swap file
    sudo swapoff -v /dev/sdXN    # For swap partition

Enabling Swap at Boot​

Ensure that swap space is activated at boot.

  • Add the swap file or partition entry to /etc/fstab:
    /swapfile none swap sw 0 0    # For swap file
    /dev/sdXN none swap sw 0 0    # For swap partition

Swappiness​

Swappiness determines how aggressively the system uses swap space.

  • Check swappiness value:

    cat /proc/sys/vm/swappiness

  • Change swappiness value (e.g., set it to 10):

    sudo sysctl vm.swappiness=10

Swapiness Values​

  • 0: Only use swap space when the RAM is fully utilized.
  • 100: Use swap space as much as possible.

Swap Space Command-Line​

  • Display swap space information:

    swapon --show

  • Check system-wide swap usage:

    free -h

  • Create a swap file (e.g., 2GB):

    sudo fallocate -l 2G /swapfile
    sudo chmod 600 /swapfile
    sudo mkswap /swapfile
    sudo swapon /swapfile

  • Create a swap partition and activate it:

    sudo mkswap /dev/sdXN
    sudo swapon /dev/sdXN

  • Disable swap space:

    sudo swapoff -v /swapfile   # For swap file
    sudo swapoff -v /dev/sdXN    # For swap partition

  • Add swap space to /etc/fstab for boot-time activation.

  • Check swappiness value:

    cat /proc/sys/vm/swappiness

  • Change swappiness value (e.g., set it to 10):

    sudo sysctl vm.swappiness=10

Conclusion​

This cheat sheet covers common concepts and commands for managing swap space in Linux. Swap space is crucial for ensuring system stability and performance when RAM is limited; refer to the Linux documentation or man pages for more in-depth information and advanced usage.