How to Resolve Linux Out‑of‑Memory Issues with a Swap Partition

A 2c2g Alibaba Cloud server hosting a Java backend, Nginx, MySQL and Redis crashes within hours because physical memory is exhausted. Adding swap can relieve pressure, though it may reduce performance, so upgrading hardware is preferable when possible.

One‑click script

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 && \
sudo chmod 600 /swapfile && \
sudo mkswap /swapfile && \
sudo swapon /swapfile && \
sudo echo '/swapfile none swap sw 0 0' >> /etc/fstab && \
sudo echo 'vm.swappiness=10' >> /etc/sysctl.conf

Swap size recommendation

Swap partition size is suggested to be 1–2 times the physical memory.

Create the swap file

Use the dd command to allocate a file of the desired size. For a 2 GB swap file:

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

Here /swapfile is the file path, bs=1M writes 1 MB per block, and count=4096 creates 4096 MB (≈2 GB) of space.

Set permissions

sudo chmod 600 /swapfile

Only the root user can read or write the swap file, improving security.

Format the file

sudo mkswap /swapfile

This command prepares the file as swap space.

Activate the swap

sudo swapon /swapfile

The swap file becomes active immediately.

Persist across reboots

Add the following line to /etc/fstab so the swap is enabled at boot:

sudo echo '/swapfile none swap sw 0 0' >> /etc/fstab

Adjust swappiness

The swappiness kernel parameter controls how aggressively the system uses swap (range 0–100, default 60). To reduce swap usage, set it to a lower value, e.g., 10.

Temporary change: sudo sysctl vm.swappiness=10 Permanent change: add or modify the line in /etc/sysctl.conf:

sudo echo 'vm.swappiness=10' >> /etc/sysctl.conf

Then edit /etc/sysctl.conf with a text editor, save, and the new value takes effect after a reboot or by running sysctl -p.