Create a Swap File on a Linux VPS

Why add swap

Swap is disk space that Linux uses when RAM is full. It does not replace RAM, but it can stop programs from being killed when memory runs out. It is useful on small VPS plans.

Step 1: Check the current swap

sudo swapon --show

free -h

If swapon --show prints nothing, you have no swap.

Step 2: Check the free disk space

df -h

Step 3: Create the swap file

Create a file of 1.5 GB (change the size as you like):

sudo fallocate -l 1.5G /swap.img

Check it:

ls -lh /swap.img

Step 4: Turn it on

Only root should read the file:

sudo chmod 600 /swap.img

Prepare it as swap:

sudo mkswap /swap.img

Turn it on:

sudo swapon /swap.img

Step 5: Make it permanent

Open /etc/fstab:

sudo nano /etc/fstab

Add this line at the end:

/swap.img none swap sw 0 0

Step 6: Check it

sudo swapon --show

free -h

Adjust swappiness

The swappiness value (0-100) says how eagerly the system uses swap. A low value means swap is used less. For servers, 10-20 is common.

Check the value:

cat /proc/sys/vm/swappiness

Set it for now:

sudo sysctl vm.swappiness=20

Make it permanent. Open sudo nano /etc/sysctl.conf and add:

vm.swappiness=20

Adjust the cache pressure

vfs_cache_pressure controls how quickly the system frees the cache of file names. The default is 100.

cat /proc/sys/vm/vfs_cache_pressure

sudo sysctl vm.vfs_cache_pressure=120

To keep it, add vm.vfs_cache_pressure=120 to /etc/sysctl.conf too.

Remove the swap file

sudo swapoff /swap.img
sudo rm /swap.img

Then delete the line from /etc/fstab.

Quick recap

• Make the file, set mode 600, run mkswap and swapon.
• Add the line to /etc/fstab.
• Tune vm.swappiness.