How to Add Swap Memory in Ubuntu 20.04

Swap memory is a portion of storage used as virtual memory when your server's RAM is fully utilized. It helps prevent crashes by moving less-used processes from RAM to swap space, keeping the system stable under heavy load.

This article shows how to add swap memory on Ubuntu 20.04 using a swap file and Vultr Block Storage to expand your server’s available memory.

Prerequisites

Before you begin:

• Have an Ubuntu 20.04 server.

• Have an existing block storage.

• Access the server using SSH as a non-root user with sudo privileges.

View Existing Swap Memory

Follow the steps below to check existing swap usage before adding more.

View the available server memory including RAM and Swap using the free utility.

$ sudo free -h

Verify the Swap memory available on your server similar to the output below.

                  total        used        free      shared  buff/cache   available
    Mem:          955Mi       317Mi       201Mi       1.2Mi       598Mi       638Mi
    Swap:         2.3Gi       268Ki       2.3Gi

Based on the above output, the server includes a 2GB Swap memory volume.

Create Swap Memory

Swap memory is storage space—either on your server's disk or a block storage volume—used as virtual memory. Utilize the section below to create swap space with a swap file or a dedicated block storage volume.

Create Swap Memory using a Swapfile

1. Create a new Swapfile with a specific size such as 2GB using the fallocate utility in your root directory /.

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   $ sudo fallocate -l 2G /swapfile.img
   

2. Modify the Swapfile permissions to allow only the root user to read and write changes on the file.

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   $ sudo chmod 0600 /swapfile.img
   

3. Format the file as swap using mkswap.

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   $ sudo mkswap /swapfile.img
   

4. Verify the new swam memory size, label information and UUID similar to the following output.

   Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
   no label, UUID=2ed3e083-fac2-4571-bbdf-e9967aa1fc03

Create Swap Memory using Vultr Block Storage

1. List the storage devices available on your server using the lsblk utility. The new disk is attached as /dev/vdb and it has no partitions.

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   $ lsblk
   

   Output:

   NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
   sr0     11:0    1 1024M  0 rom
   vda    253:0    0   25G  0 disk
   ├─vda1 253:1    0  512M  0 part /boot/efi
   └─vda2 253:2    0 24.5G  0 part /
   vdb    253:16   0    40G  0 disk

   The Vultr Block Storage device is attached as vdb based on the above output with a 40GB size.

2. Initialize the volume using the GPT partition table.

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   $ sudo parted -s /dev/vdb mklabel gpt
   

3. Create a new partition using the entire block storage volume.

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   $ sudo parted -s /dev/vdb unit mib mkpart primary 0% 100%
   

4. List the server storage devices again and verify that the new block storage partitiion is available.

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   $ lsblk
   

   Output:

   NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
   sr0     11:0    1 1024M  0 rom  
   vda    253:0    0   25G  0 disk 
   ├─vda1 253:1    0  512M  0 part /boot/efi
   └─vda2 253:2    0 24.5G  0 part /
   vdb    253:16   0   40G  0 disk 
   └─vdb1 253:17   0   40G  0 part 

5. Convert the new block storage partition to swap.

   console Copy

   $ sudo mkswap /dev/vdb1
   

   Output:

   Setting up swapspace version 1, size = 40 GiB (42947571712 bytes)
   no label, UUID=7b3b6fa6-b344-41bd-b25b-f8657caa36b4

6. View your block devices information and verify that the new swap partition is available.

   console Copy

   $ sudo blkid
   

   Output:

   /dev/vda2: UUID="95e88749-c308-4c15-aca0-f47049d0c699" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="48874572-7e1f-4766-93e7-431038bd78f3"
   /dev/vda1: UUID="D587-7645" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="96ca28e5-4696-482c-9359-24b87f2ea53e"
   /dev/vdb1: UUID="ca230c16-b5a4-44e6-b5a8-930bb1f33fcf" TYPE="swap" PARTLABEL="primary" PARTUUID="7897c216-dc99-4e91-be17-abc1a0dba849"

   Note the swap partition UUID value to use when mounting the volume automatically at boot time.

Enable Swap Memory

1. Enable the Swapfile as swap memory using the swapon utility.

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   $ sudo swapon /swapfile.img
   

2. View the server swap memory and verify that the new Swapfile is active.

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   $ sudo swapon -s
   

   Output:

   Filename                                Type            Size            Used            Priority
   /swapfile                               file            2457596         268             -2
   /swapfile.img                           file            2097148         0               -3

3. Run the following command to enable the Vultr Block Storage swap partition as swap memory. Replace /dev/vdb1 with your actual partition path.

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   $ sudo swapon /dev/vdb1
   

4. View the server swap memory and verify that the swap partition is active.

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   $ sudo swapon -s
   

   Output:

   Filename                                Type            Size            Used            Priority
   /swapfile                               file            2457596         268             -2
   /swapfile.img                           file            2097148         0               -3
   /dev/vdb1                               partition       41940988        0               -4

Configure the File System Table (fstab) to Enable Automatic Mounting

The fstab file controls how file systems mount at boot. Follow the steps below to configure it for automatically mounting your swap memory at startup.

1. Backup the original fstab configuration on your server.

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   $ sudo cp /etc/fstab /etc/fstab.bak
   

2. Open the fstab configuration file using a text editor such as nano.

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   $ sudo nano /etc/fstab
   

3. Add the following Swapfile configuration at the end of the file.

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   /swapfile.img swap swap defaults 0 0
   

   Save and close the file.

   The above configuration enables automatic mounting using the /swapfile.img file. Within the configuration:

   • swap: Enables the swap file system type.
   • swap: Sets the swap mount point.
   • 0: Disables backups on the swap file system.
   • 0: Disables file system checks on the swap memory.

4. View your block devices information and copy the UUID of new /dev/vdb1.

   console Copy

   $ sudo blkid
   

   Output:

   /dev/vda2: UUID="95e88749-c308-4c15-aca0-f47049d0c699" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="48874572-7e1f-4766-93e7-431038bd78f3"
   /dev/vda1: UUID="D587-7645" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="96ca28e5-4696-482c-9359-24b87f2ea53e"
   /dev/vdb1: UUID="ca230c16-b5a4-44e6-b5a8-930bb1f33fcf" TYPE="swap" PARTLABEL="primary" PARTUUID="7897c216-dc99-4e91-be17-abc1a0dba849"

5. Add the block storage swap partition using its UUID value to enable automatic mounting on the volume.

   ini Copy

   UUID=ca230c16-b5a4-44e6-b5a8-930bb1f33fcf       swap    swap    sw      0       0
   

   Replace UUID=ca230c16-b5a4-44e6-b5a8-930bb1f33fcf with your server block device UUID.

   You have enabled automatic mounting of swap memory on your server. The server automatically mounts and enables the swap memory at boot time.

Configure Swappiness

The swappiness setting controls how aggressively your server uses swap memory compared to RAM. Lower values reduce swap usage, while higher values increase it. Below is a breakdown of how the values behave:

• 0: Avoids swapping unless absolutely necessary.
• 1–49: Uses swap sparingly; prefers RAM until nearly full.
• 50: Balanced use of RAM and swap.
• 51–99: More aggressive swapping from RAM to swap.
• 100: Prioritizes swap usage; RAM is freed more frequently.

Follow the steps below to configure the swappiness value on your server.

1. Run the following command to modify the /etc/sysctl.conf with your swappiness value. Replace 50 with your desired swapping level.

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   $ echo "vm.swappiness = 50" | sudo tee -a /etc/sysctl.conf
   

   Output:

   vm.swappiness = 50

2. Reload the sysctl configuration to apply the configuration changes.

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   $ sudo sysctl -p
   

Test the Swap Memory

1. View all available swap volumes on your server.

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   $ sudo swapon -s
   

   Output:

   Filename                                Type            Size            Used            Priority
   /swapfile                               file            2457596         268             -2
   /swapfile.img                           file            2097148         0               -3
   /dev/vdb1                               partition       41940988        0               -4

2. Run the following command to activate all inactive swap volumes in your /etc/fstab configuration.

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   $ sudo swapon -a
   

3. View your server memory and verify the amount of swap memory actively in use.

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   $ sudo free -h
   

   Output:

                  total        used        free      shared  buff/cache   available
   Mem:           955Mi       348Mi       155Mi       1.2Mi       613Mi       607Mi
   Swap:           44Gi       268Ki        44Gi

Remove Swap Memory

1. Disable swap using the swapoff command followed by the swap file or partition path. For example, to disable the default swap file.

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   $ sudo swapoff /swapfile
   

2. View the swap volumes on your server and verify that the default Swapfile is disabled.

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   $ sudo swapon -s
   

   Output:

   Filename                                Type            Size            Used            Priority
   /swapfile.img                           file            2097148         0               -2
   /dev/vdb1                               partition       41940988        0               -3

Conclusion

You’ve successfully added swap memory on an Ubuntu 20.04 server, extending your system’s available memory. While swap is slower than RAM, it helps maintain performance by offloading less-used or resource-intensive processes from main memory.