I would like to increase swap size on my centos or rhel system. How Do I create a SWAP file to increase swap space under linux operating system? How to add a swap file on CentOS 7/6.5 or RHEL 7/6.5 linux? this guide will show you how to add a swap file and enable the swap file to current system.
You need to use dd command to create swap file firstly and then using mkswap command to setup a linux swap area in that swap file.
CentOS/RHEL Create a Swap File
Step1# Checking the current swap size by runnging the following command:
cat /proc/meminfo | grep -i swap
or
free
Outputs:
[root@devops ~]# cat /proc/meminfo | grep -i swap SwapCached: 9600 kB SwapTotal: 2129916 kB SwapFree: 2054652 kB [root@devops ~]# free total used free shared buffers cached Mem: 1018256 947056 71200 1780 20 187616 -/+ buffers/cache: 759420 258836 Swap: 2129916 75264 2054652
Step2# using “dd” command to create a 100MB SWAP file, type:
dd if=/dev/zero of=/swaptest bs=1M count=100
outputs:
[root@devops /]# dd if=/dev/zero of=swaptest bs=1M count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 0.255226 s, 411 MB/s
Step3# seting up a linux swap area in above swaptest file
You can use “mkswap” command to setup a linux swap area, issue the following command:
mkswap /swapfile
outputs:
[root@devops /]# mkswap swaptest Setting up swapspace version 1, size = 102396 KiB no label, UUID=490f1d73-b207-4727-8eac-5a08f57a865f
Step4# Enabling swaptest file for swaping, issue the following command:
swapon /swaptest
outputs:
[root@devops /]# swapon /swaptest swapon: /swaptest: insecure permissions 0644, 0600 suggested.
Form above outputs, you will find that the default permission of swaptest is 0644, and it’s insecure. so type the following command to change file permission as 0600.
chmod 600 /swaptest
Step5# checking the swap space again by runnging the following command:
cat /proc/meminfo | grep -i swap
outputs:
[root@devops /]# cat /proc/meminfo | grep -i swap SwapCached: 10164 kB SwapTotal: 2232312 kB SwapFree: 2157380 kB
If you want to enable the swaptest file while system starts up, then you need to add the below configuraton into “/etc/fstab” file.using vim command to edit “/etc/fstab” file:
vim /etc/fstab
Adding the following line:
/swaptest none swap sw 0 0
Now when system reboot, the swaptest swap area will enable automatically.
If you want to disable swap file for swapping, you can use swapoff command,type:
swapoff /swaptest
done….