This tutorial explains how to setup SWAP on CentOS 7.
SWAP or swap space in Linux is virtual memory, which is used when the amount of physical memory (RAM) is fully used up. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. Swap space can help machines with a small amount of RAM. However, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a significantly slower access time than physical memory. When your system runs out of free physical memory (RAM), your application might start crashing if there is no swap space allocated on your machine. Using swap space will allow your applications to continue running, however, intense swap space usage may drastically reduce your server performance.
- RHEL / CentOS Linux 6, 7 OS.
- Recommended System Swap Space
- Create a swap file.
- Enable swapping.
1. Recommended System Swap Space.
|Amount of RAM in the System||Recommended Amount of Swap Space|
|4GB of RAM or less||a minimum of 2GB of swap space|
|4GB to 16GB of RAM||a minimum of 4GB of swap space|
|16GB to 64GB of RAM||a minimum of 8GB of swap space|
|64GB to 256GB of RAM||a minimum of 16GB of swap space|
|256GB to 512GB of RAM||a minimum of 32GB of swap space|
2. Setup swap.
Let’s say our CentOS 7 machine has 8 GB of RAM. We will setup the minimum recommended 4 GB file for swapping.
First, allocate 4 GB of disk space to our swap file.
fallocate -l 4G /swap_space
Then, modify the permissions so that only the owner of the file (in this case
root) can use the file for swapping.
chmod 600 /swap_space
Now, we need to setup the swap file on our system using the
3. Enable swapping.
All that is let now is to enable our swap file using the
swapon command. Use the
swapoff command to disable the swap file or
swapoff -a to disable all swap devices.
NOTE: To enable our swap file boot time, edit
/etc/fstab by including the following line at the end of the file:
/swap_space swap swap defaults 0 0
You can check if your newly assigned swap file enabled by using the
free -h or
cat /proc/swaps commands.