Create, Resize or Remove a Swap File on Linux

sudo fallocate -l 4G /swapfile        # use dd if fallocate fails (see below)
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
echo '/swapfile none swap defaults 0 0' | sudo tee -a /etc/fstab
swapon --show

Check what swap you already have

Before adding anything, see what's active. Many systems already have a swap partition, a swap file or zram.

swapon --show
free -h
cat /proc/sys/vm/swappiness
lsblk -f | grep -i swap

Example output:

NAME       TYPE      SIZE USED PRIO
/swap.img  file        4G   0B   -2
/dev/zram0 partition 7.7G 1.2G  100

A /dev/zram0 entry means compressed RAM swap (default on Fedora). /swap.img or /swapfile is a file (Ubuntu installs one by default). A /dev/sdX or /dev/nvme0n1pX entry is a partition. Higher PRIO is used first. Check which filesystem holds your root with findmnt -no FSTYPE /: the method differs on Btrfs.

Create a swap file on ext4 or XFS

1. Allocate the file

sudo fallocate -l 4G /swapfile

fallocate reserves blocks instantly. If swapon later complains that the file "has holes", or you are on an unusual filesystem, create it with dd, which writes real zeros:

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 status=progress

2. Lock down permissions

sudo chmod 600 /swapfile

Swap can contain passwords and keys from memory, so only root may read it. swapon warns about "insecure permissions" otherwise.

3. Format and enable it

sudo mkswap /swapfile
sudo swapon /swapfile

4. Make it permanent

echo '/swapfile none swap defaults 0 0' | sudo tee -a /etc/fstab
sudo systemctl daemon-reload
sudo swapoff /swapfile && sudo swapon -a && swapon --show

The last line proves the fstab entry works before you reboot. For more on fstab syntax, see the disk management guide.

Resize or remove an existing swap file

You can't grow an active swap file in place. Turn it off, recreate it at the new size, and turn it back on. The path in fstab stays the same, so you don't need to edit it.

# Ubuntu's default file is /swap.img; others use /swapfile
sudo swapoff /swap.img
sudo rm /swap.img
sudo fallocate -l 8G /swap.img
sudo chmod 600 /swap.img
sudo mkswap /swap.img
sudo swapon /swap.img
swapon --show

To remove swap entirely: sudo swapoff /swapfile, delete its line from /etc/fstab, then sudo rm /swapfile. Remove the fstab line before rebooting or systemd will wait for a missing swap device.

Swap file on Btrfs

Fedora, openSUSE and many Arch installs use Btrfs. A Btrfs swap file must be No_COW, not compressed, on a single device, and on a subvolume that is not snapshotted (an active swap file blocks snapshots of its subvolume). With btrfs-progs 6.1 or newer, one command handles the details:

# a dedicated subvolume keeps the file out of root snapshots
sudo btrfs subvolume create /swap
sudo btrfs filesystem mkswapfile --size 4g --uuid clear /swap/swapfile
sudo swapon /swap/swapfile
echo '/swap/swapfile none swap defaults 0 0' | sudo tee -a /etc/fstab

On older btrfs-progs, do it manually: sudo truncate -s 0 /swap/swapfile, sudo chattr +C /swap/swapfile, then dd, chmod 600 and mkswap as above. The +C attribute must be set while the file is still empty.

If your root subvolume is mounted from @ (Ubuntu-style layouts used by Timeshift), create the swap subvolume at the top level and mount it separately, so Timeshift and Snapper snapshots don't include it.

Tune swappiness

vm.swappiness (0–200, default 60) controls how readily the kernel swaps out anonymous memory compared with dropping file cache. Lower values keep applications in RAM longer; it does not disable swap.

# try it now
sudo sysctl vm.swappiness=10
# make it permanent
echo 'vm.swappiness=10' | sudo tee /etc/sysctl.d/99-swappiness.conf
sudo sysctl --system

Per-distro notes and zram

zram creates a compressed block device in RAM and uses it as swap. A 2:1 to 3:1 compression ratio is typical, so 8 GB of RAM behaves like noticeably more. It's handled by zram-generator ([email protected]).

Ubuntu, Debian and Linux Mint

Ubuntu's installer creates /swap.img on ext4 installs. Debian's installer usually creates a swap partition. Mint creates /swapfile. To add zram:

sudo apt install systemd-zram-generator
sudo tee /etc/systemd/zram-generator.conf <<'EOF'
[zram0]
zram-size = min(ram / 2, 8192)
compression-algorithm = zstd
EOF
sudo systemctl daemon-reload
sudo systemctl start [email protected]
swapon --show

Older guides use zram-tools or zram-config. Pick one zram tool only; don't install several.

Fedora

Fedora enables zram by default through zram-generator-defaults and creates no disk swap. Change the size by creating /etc/systemd/zram-generator.conf (it overrides /usr/lib/systemd/zram-generator.conf), then restart [email protected]. Fedora's root is Btrfs, so add disk swap with the Btrfs method. You only need it if you want hibernation or extra overflow.

Arch Linux

Arch creates nothing by default. Use a swap file (ext4 or Btrfs method) and/or zram: sudo pacman -S zram-generator, then write the same zram-generator.conf as above. The Arch Wiki Swap and zram pages cover edge cases.

openSUSE

The installer normally creates a swap partition next to Btrfs root. To add a file, use the Btrfs method with a dedicated subvolume so Snapper doesn't snapshot it. zram is available as zram-generator via sudo zypper install zram-generator.

Swap for hibernation

Hibernation writes RAM to disk swap (not zram), so swap must be at least as big as the memory in use. With a swap file, the kernel also needs to know where it is:

# UUID of the filesystem holding the swap file
findmnt -no UUID -T /swapfile
# physical offset (ext4): start of the first extent
sudo filefrag -v /swapfile | awk '$1=="0:" {print substr($4, 1, length($4)-2)}'
# physical offset on Btrfs
sudo btrfs inspect-internal map-swapfile -r /swap/swapfile

Add resume=UUID=<uuid> resume_offset=<offset> to your boot parameters (see how to set kernel parameters) and rebuild the initramfs. Recent systemd can find the swap device on its own on some setups, but setting it explicitly is the reliable option. If resume fails, the suspend and hibernate troubleshooting guide covers Secure Boot lockdown and NVIDIA issues.

Verify it works

swapon --show
free -h
cat /proc/swaps
# zram stats: original vs compressed size
zramctl
# after a reboot, check that fstab swap came up
systemctl list-units --type swap

Swap is working if swapon --show lists it after a reboot. Some USED on a busy machine is normal and not a problem on its own. Constant heavy swapping (watch the si/so columns in vmstat 1) means you need more RAM or need to find the memory hog. See finding what's using CPU and memory.

Common problems

If programs still die with "Cannot allocate memory" while free RAM and swap look fine, the cause is usually overcommit limits or cgroup memory caps, not swap size.

Frequently asked questions