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Vultr profile image Sanskriti Harmukh
Sanskriti Harmukh for Vultr

Posted on Originally published at docs.vultr.com

Adding Swap Memory on Ubuntu 26.04

#linux #ubuntu #devops #sysadmin

Servers with limited RAM are vulnerable to out-of-memory kills during traffic spikes or memory-intensive workloads. Swap provides an overflow area on disk, giving the kernel room to move inactive memory pages before resorting to terminating processes. This guide configures a 2 GB swap file on Ubuntu 26.04, mounts it persistently via /etc/fstab, and sets the swappiness value to a level appropriate for server workloads.

Check Current Swap

Verify memory and swap status before making any changes:

$ free -h
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A Swap: 0B line confirms no swap is currently configured.

Create a Swap File

Allocate a 2 GB file, set the correct permissions, and format it as swap:

1. Create a 2 GB file:

$ sudo fallocate -l 2G /swapfile
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2. Restrict file permissions:

$ sudo chmod 600 /swapfile
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The chmod 600 restricts access to root only. Swap files with world-readable permissions will be rejected by the kernel.

3. Format the file as swap:

$ sudo mkswap /swapfile
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Enable Swap

Activate the swap file and confirm it is recognized by the system:

1. Activate the swap file:

$ sudo swapon /swapfile
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2. Verify swap is active:

$ sudo swapon --show
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3. Confirm the allocation:

$ free -h
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The Swap line should now show 2.0Gi total.

Configure Automatic Mounting at Boot

Swap activated with swapon does not persist across reboots without an /etc/fstab entry.

1. Back up the fstab file:

$ sudo cp /etc/fstab /etc/fstab.bak
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2. Add the swap entry:

$ echo '/swapfile swap swap defaults 0 0' | sudo tee -a /etc/fstab
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3. Verify the entry was written correctly:

$ grep swap /etc/fstab
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Tune Swappiness

Swappiness controls how aggressively the kernel moves memory pages to swap. The value ranges from 0 to 100.

  • 0 — only swap when RAM is critically full
  • 10 — recommended for servers (keeps more data in RAM)
  • 60 — Ubuntu default (more aggressive)
  • 100 — swap as aggressively as possible

1. Check the current value:

$ cat /proc/sys/vm/swappiness
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2. Set the swappiness value:

$ sudo nano /etc/sysctl.conf
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Add the following line:

vm.swappiness=10
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3. Apply the change immediately:

$ sudo sysctl -p
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Next Steps

Swap is now active and persists across reboots. From here you can:

  • Monitor swap usage in real time with vmstat 1 during peak load periods
  • Increase swap size by repeating these steps with a larger fallocate value
  • Explore zswap or zram for in-memory compression as an alternative to disk-backed swap

For the complete guide, visit the original article on Vultr Docs.

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