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How to enable Swap on a Linux VPS

This page shows you how to add swap to a Linux server that has none. You can do it while the server is running, without stopping Hiddify.

Swap is space on the disk that Linux uses as extra memory when the RAM is full. It is much slower than RAM, but it stops programs from crashing when memory runs out.

When you need this

  • Symptom: installing or updating Hiddify Manager stops with Building the admin UI ran out of memory (needs ~1.2 GB free RAM or swap), or services on a small server stop or restart for no clear reason.
  • Likely cause: the server has little RAM (for example 1 GB) and no swap.
  • Fix: add a swap file using the steps below, then run the install or update again.

Before you start

Steps

Run all commands on your server, over SSH.

  1. Check whether the server already has swap:

    sudo swapon --show

    If the output is empty, there is no swap; continue. If it lists a swap file or partition, you already have swap and do not need this page (you can check its size with free -h).

  2. Check the free disk space:

    df -h /

    Look at the Avail column. You need more free space than the swap size you want, plus some room to spare.

  3. Create a 2 GB file for swap:

    sudo fallocate -l 2G /swapfile

    If this prints an error such as fallocate failed: Operation not supported, use this command instead:

    sudo dd if=/dev/zero of=/swapfile bs=1M count=2048

    If it says the file already exists, run sudo swapon --show again: the file may already be in use.

  4. Allow only the system administrator to read the file:

    sudo chmod 600 /swapfile

  5. Prepare the file as swap:

    sudo mkswap /swapfile

  6. Turn the swap on:

    sudo swapon /swapfile

  7. Check that it worked:

    sudo swapon --show

    It worked if you see /swapfile with a size of about 2G.

  8. Keep the swap after a reboot by adding it to /etc/fstab (the file that lists what Linux turns on at startup). This command adds the line only if it is not there yet:

    grep -q '^/swapfile ' /etc/fstab || echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Notes

  • Size: pick the swap size based on your server's RAM and free disk space. 2 GB is enough for the Hiddify installer on a small server.
  • Watch usage: check memory and swap use at any time with free -h or htop. If swap is always heavily used, the server needs more RAM. See How to monitor server resources.
  • Some servers cannot use swap. On some container-based VPS types (such as OpenVZ or LXC), swapon fails with Operation not permitted. In that case, ask your provider or choose a plan with more RAM.
Last update: November 6, 2026

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