How to clear the Swap memory of a Linux server

Sometimes we may receive resource usage alerts indicating that the server's Swap or Exchange Memory is at 100% usage.

SERVICE ALERT: ce00000000000.dnssw.net
Unix Memory Nou
WARNING
Usage: real 95% (11404/11995 MB), buffer: 3 MB, cache: 302 MB, swap: 100% (1907/1907 MB)

This commonly happens in two scenarios:

1. The server has run out of RAM and is or has been writing to Swap.
2. The software installed on the server, due to its own configuration, is or has been writing to Swap.

danger ⚠️ The actions performed below may be dangerous if you do not have the necessary knowledge ⚠️

How to detect the alert

If you have Advanced Monitoring, you will have received an email notifying you of the Unix Memory Nou alert.

SERVICE ALERT: ce00000000000.dnssw.net
Unix Memory Nou
WARNING
Usage: real 95% (11404/11995 MB), buffer: 3 MB, cache: 302 MB, swap: 100% (1907/1907 MB)

Handbuch: How to Activate Advanced Monitoring on my Cloud server with SWPanel and view its Dashboard.

How to handle the alert

To handle the alert, you must connect to your server via console. You can connect via the SWPanel Console [Handbuch: How do I access my Cloud using the console via SWPanel] or via SSH [Handbuch: Connect to your Cloud via console using PuTTY].

To clear the Swap memory, we must dump the data stored in the RAM memory.

First of all, we must check the state of the server's memory using the following command:

free -m

With this, we can see the memory bytes assigned, available, and used.

In this case, the server has 453B occupied and 1453B free:

We must ensure that the amount of Swap used is less than the amount of RAM available.

In this case, this rule is met; we have 453B of Swap in use and 3379B of RAM available:

danger ⚠️ Do not perform the following step if the previous rule is not met ⚠️

If the previous rule is met, we will proceed to dump the Swap into the RAM and, in this way, clear it. We will use the following command:

swapoff -a && swapon -a

When executing the command, the console will remain 'inactive' until the process finishes:

The process of clearing the Swap may take several minutes depending on the state of the server and its resources.

You can view the clearing process in real-time by opening another console and using the command:

watch -n0 free -m