SWAP memory is used to help RAM, once it can not store any more data. The data which can not be stored in RAM is then stored to SWAP memory in the hard disk. In this article, we will provide the basic steps of how to modify and increase SWAP memory in our VPS.

In general, there are different opinions on how much SWAP memory your server should have. It could be half of your RAM, the same amount, or even more than RAM. In our article, we will assign 6 GB of SWAP to the server.

Allocating SWAP memory

The first thing you should do is to check if there is no SWAP memory in use on your server with the following command:

your results will be printed in two lines: “Mem”, “Swap”, which will indicate what is the exact amount of RAM and SWAP memory on the server. The “Swap” line should only contain zeros.

With the following command we will allocate 6 GB of disk space for our SWAP memory:

You can check if your SWAP memory was assigned with this command:

At first, your SWAP may not be allocated due to a permission issue and you might be seeing this message:

-rw-r--r-- 1 root root 6.0G Dec 5 14:32 /swapfile

This would suggest we have to make additional changes, first of which should be changing the permission of the swapfile:

After the change you can check the file permissions again:

The results should change as well, comparing to the previous above:

-rw------- 1 root root 6.0G Dec 5 14:36 /swapfile

We can now check if the SWAP memory was allocated correctly:

Y

our results will print two lines again, just this time, you will see a line “Swap” having a variable of 6 GB.

Additional options

In general, your SWAP memory allocation may stop working after you reboot the server, so in order to save these changes permanently, we have to edit /etc/fstab. But first, we would recommend making a backup of this file:

Once the backup is done, we have made the changes to the actual file:

There are a few extra options for SWAP memory, which we would like to address as well.

option – swappiness, is used to describe when the system will move data to SWAP file. The option may have a value from 0 to 100. Closer to 0, means that your data will be a move to SWAP only when it will be necessary. Closer to 100 means that, data will be moved to SWAP more often, therefore leaving RAM memory freer. We would recommend keeping this option closer to 0, for example, 10.

You can check the current value with the following command:

option – vfs_cache_pressure, this option sets how often the information about the file system is updated. By default, it should be 100, but we would recommend using low, for example, value 50.

The current value can be checked with this command:

Both of the additional options can be edited at the file /etc/sysctl.conf by adding the following line at the bottom of the file:

vm.swappiness=10
​vm.vfs_cache_pressure=50