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In this article, we explain how to configure and manage swap space in Linux. Swap space is a dedicated area on your disk that Linux uses to temporarily offload data from RAM when physical memory is low. This guide covers both swap partitions and swap files, providing the necessary commands and practical examples to help you manage them effectively.

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Understanding Swap Space Through a Scenario

Imagine a computer with 4 GB of RAM. You open a video editor that uses 2 GB of RAM and an audio editor that uses the remaining 2 GB. With no free memory left, you may wonder how you can still run additional applications like Chrome. This is where swap space becomes essential:
  • Linux monitors memory usage and identifies inactive applications (e.g., a video editor that hasn’t been used for a while).
  • It moves data from RAM to a designated swap area, for example, a 2 GB swap partition. This process frees up RAM, allowing new applications like Chrome to run.
The image illustrates the concept of managing swap space, showing RAM usage by an audio editor and Chrome, and a swap partition used by a video editor.
The scenario above is a simplified illustration that demonstrates why and how swap space is used in Linux systems.

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Setting Up a Swap Partition

Before using a swap partition, check if your system is already using swap areas: 
$ swapon --show
Since swap is not activated initially, this command may not return any output. Next, review the available partitions. For example, assume that a swap partition on /dev/vdb3 was created earlier. The following command displays your system’s block devices: 
$ lsblk
NAME                  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
vda                   252:0    0   20G  0 disk 
├─vda1                252:1    0    1M  0 part 
├─vda2                252:2    0  1.8G  0 part /boot
├─vda3                252:3    0 18.2G  0 part 
└─ubuntu--vg-ubuntu--lv 253:0    0   10G  0 lvm  /
vdb                   252:16   0   10G  0 disk 
├─vdb1                252:17   0    4G  0 part 
├─vdb2                252:18   0    4G  0 part 
└─vdb3                252:19   0    2G  0 part
This partition is currently empty. Before Linux can utilize it as swap space, you need to initialize it—similar to formatting a USB stick with FAT32 or NTFS, where a small header is written to define the file system type. Initialize the partition as swap with: 
$ sudo mkswap /dev/vdb3
Setting up swapspace version 1, size = 2 GiB (2146410496 bytes)
no label, UUID=a39c80a1-a0c6-4ba2-a4a3-8a2058d8859
Next, enable the swap partition: 
$ sudo swapon --verbose /dev/vdb3
swapon: /dev/vdb3: found signature [pagesize=4096, signature=swap]
swapon: /dev/vdb3: pagesize=4096, swapsize=2146414592, devsize=2146418176
swapon /dev/vdb3
Verify that the swap area is activated: 
$ swapon --show
NAME       TYPE      SIZE USED PRIO
/dev/vdb3 partition  2G   0B   -2
The swap configuration made above is temporary. After a reboot, the swap partition will not activate automatically unless it is added to the system’s fstab file.
To disable the swap partition when needed, use: 
$ sudo swapoff /dev/vdb3

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Creating and Using a Swap File

Linux also supports swap files, which can be an alternative to swap partitions. Many modern Ubuntu systems, for instance, use a swap file by default. Follow these steps to create and use a swap file:
  1. Create a Swap File:
    Use the dd command to create a file filled with binary zeros. The following command creates a 128 MB swap file:     
    $ sudo dd if=/dev/zero of=/swap bs=1M count=128
  2. Increase the Swap File Size:
    To create a larger swap file (e.g., 2 GB), run:     
    $ sudo dd if=/dev/zero of=/swap bs=1M count=2048 status=progress
    Example output: 
    1436549120 bytes (1.4 GB, 1.3 GiB) copied, 2 s, 717 MB/s
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB, 2.0 GiB) copied, 2.71801 s, 790 MB/s
  3. Set Correct Permissions:
    For security, restrict access so that only the root user can read and write to the swap file:     
    $ sudo chmod 600 /swap
  4. Initialize the Swap File:
    Format the file as swap space:     
    $ sudo mkswap /swap
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=cff8e9dc-54fa-4661-a48e-497610b2f07b
  5. Enable the Swap File:
    Activate the swap file with:     
    $ sudo swapon --verbose /swap
swapon: /swap: found signature [pagesize=4096, signature=swap]
swapon: /swap: pagesize=4096, swapsize=2147483648, devsize=2147483648
swapon /swap
  6. Verify Active Swap Areas:
    Check to ensure both the swap partition and swap file are active:     
    $ swapon --show
NAME        TYPE      SIZE USED PRIO
/dev/vdb3   partition  2G   0B   -2
/swap       file       2G   0B   -3

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Conclusion

By following these steps, you can effectively configure and manage both swap partitions and swap files on your Linux system. These methods help ensure that your system can handle low-memory situations efficiently, enhancing overall performance. For additional information, check out these resources:

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