Create a Linux Swap File

Swap is a space on a disk that is used when the amount of physical RAM is full. When a Linux 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 file. In most cases, when running Linux on a virtual machine, a swap partition is not present, so the only option is to create a swap file.

Swap helps when you run out of RAM, but it is not a replacement for memory. Heavy swapping usually means your system is under memory pressure and will slow down.

How to add a swap file #

Follow these steps to add 1GB of swap to your server. If you want to add 2GB instead of 1GB, replace 1G with 2G. On small systems, 1-2GB is often enough; if you use hibernation, swap should be at least the size of RAM.

1. Create a file that will be used for swap:

   Terminal

   sudo fallocate -l 1G /swapfile

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

   Terminal

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

   To confirm the file size, run:

   Terminal

   ls -lh /swapfile

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

   Terminal

   sudo chmod 600 /swapfile

   If you are using Btrfs, swap files must be created on a No_COW, non-compressed file, otherwise swapon can fail. Create the swap file inside a directory with chattr +C and compression disabled. For example:

   Terminal

   sudo mkdir -p /swap
   sudo chattr +C /swap

   Then create the swap file inside /swap (for example, /swap/swapfile).

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

   Terminal

   sudo mkswap /swapfile

4. Enable the swap with the following command:

   Terminal

   sudo swapon /swapfile

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

   /etc/fstabini

   /swapfile none swap defaults 0 0

5. To verify that the swap is active, use either swapon or the free command as shown below:

   Terminal

   sudo swapon --show

   output

   NAME      TYPE  SIZE   USED PRIO
   /swapfile file 1024M 507.4M   -1

   Terminal

   sudo free -h

   output

                 total        used        free      shared  buff/cache   available
   Mem:           488M        158M         83M        2.3M        246M        217M
   Swap:          1.0G        506M        517M

How to adjust the swappiness value #

Swappiness is a Linux kernel 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 kernel try to avoid swapping whenever possible, while a higher value will make the kernel 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/vm/swappiness

60

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

For example, to set the swappiness value to 10, you would run the following sysctl command:

sudo sysctl vm.swappiness=10

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

vm.swappiness=10

The optimal swappiness value depends on your system workload and how the memory is being used.

How to remove a swap file #

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

1. First, deactivate the swap by typing:

   Terminal

   sudo swapoff -v /swapfile

2. Remove the swap file entry /swapfile none swap defaults 0 0 from the /etc/fstab file.

3. Finally, delete the actual swap file using the rm command:

   Terminal

   sudo rm /swapfile

FAQ #

How much swap space should I create?
For systems with less than 2 GB of RAM, a swap size of twice the RAM is a common starting point. For systems with 2–8 GB of RAM, matching the RAM size is usually enough. For systems with more than 8 GB of RAM, 4–8 GB of swap is a reasonable ceiling unless you use hibernation, in which case swap must be at least the size of your RAM.

How do I resize an existing swap file?
Turn off the current swap, recreate the file at the new size, reformat it, and re-enable it:

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

My system already has a zram device. Can I still add a swap file?
Yes. Ubuntu 22.04 and later (and Debian 12 and later) enable a zram-based swap device by default. You can add a swap file alongside it using the same steps above. If you run swapon --show and see a /dev/zram entry instead of a file, that is expected. The new swap file will appear as an additional entry once enabled.

Conclusion #

For more on memory management, the free and vmstat commands give you a live view of swap usage. If your system is swapping heavily under normal load, adding more RAM is a more effective fix than increasing swap.

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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