Create a Swap File on Linux

Thu, 11 Aug 2022 01:21:50 +0800

A swap file lets the kernel move idle pages out of RAM onto disk. It’s handy on small-memory hosts (VPS, VMs) that have no dedicated swap partition, and unlike a partition it can be resized or removed without repartitioning.

Create the swap file

# Allocate a 1 GiB file. dd is preferred over fallocate here because
# swapon rejects files with holes on some filesystems (e.g. ext4, XFS).
dd if=/dev/zero of=/swapfile bs=1M count=1024 status=progress

chmod 0600 /swapfile   # only root may read/write the swap file
mkswap /swapfile       # format it as swap space
swapon /swapfile       # enable it immediately

Make it persistent

Add an entry to /etc/fstab so the swap file is mounted on every boot. The grep guard keeps this idempotent — running it twice won’t add a duplicate line.

Linux on Terence's blog

Create a Swap File on Linux

Create the swap file

Make it persistent