Swap is a physical space on the disk that is used when the system RAM is full. When the memory usage in a system exceeds the available RAM, the kernel will move the idle page to the swap memory. Swap space can be created on a separate partition or a swap file. If your server is running on a VPS and a swap partition is not present, then you will need to create a swap file.
In this post, we will show how to create and manage a swap space on Linux.
Step 1 – Verify Swap Partition
Before starting, you will need to check whether Swap is enabled or not in your system.
You can check it with the following command:
swapon --show
If the output is empty that means there is not any swap space active in your system.
Step 2 – Create a Swap File
As you can see, there is not any swap space active in your system. So you will need to create a new swap file to your system.
First, create a swap file with size 4GB using the following command:
dd if=/dev/zero of=/swapfile bs=4096 count=1048576
You should see the following output:
1048576+0 records in 1048576+0 records out 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 9.47796 s, 453 MB/s
Next, set the correct permission on swapfile with the following command:
chmod 600 /swapfile
Next, create a swap area on the swapfile with the following command:
mkswap /swapfile
Output:
Setting up swapspace version 1, size = 4 GiB (4294963200 bytes) no label, UUID=035ada64-2c1a-407d-9f1a-c0dd02b8dcd4
Next, activate the swap space using the following command:
swapon /swapfile
The above command will activate the swap space temporarily.
To set up it permanently, edit the /etc/fstab file:
nano /etc/fstab
Add the following line:
/swapfile swap swap defaults 0 0
Save and close the file then verify the swap partition with the following command:
swapon --show
You should see the following output:
NAME TYPE SIZE USED PRIO /swapfile file 4G 0B -2
Step 3 – Check Swap Usage
To check the Swap usage information, run the following command:
free -m
You should see the following output:
total used free shared buff/cache available Mem: 1987 74 69 0 1843 1745 Swap: 4095 0 4095
You can also check it with the following command:
cat /proc/swaps
You should see the following output:
Filename Type Size Used Priority /swapfile file 4194300 0 -2
You can also use the top command to check the swap usage in real-time:
top
You should see the following output:
Tasks: 84 total, 1 running, 83 sleeping, 0 stopped, 0 zombie %Cpu(s): 5.9 us, 5.9 sy, 0.0 ni, 88.2 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st MiB Mem : 1987.7 total, 68.0 free, 74.8 used, 1844.9 buff/cache MiB Swap: 4096.0 total, 4096.0 free, 0.0 used. 1745.5 avail Mem
You can also use the vmstat command to check the swap usage:
vmstat 2 6
You should see the following output:
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 3 0 0 69356 12096 1877228 0 0 35 652 31 59 0 0 99 0 0 0 0 0 69420 12096 1877228 0 0 0 0 24 42 0 0 100 0 0 0 0 0 69388 12096 1877228 0 0 0 0 22 40 0 0 100 0 0
Step 4 – Remove a Swap Space
In order to remove the swap space, you will need to deactivate the swap space first. You can do it with the following command:
swapoff -v /swapfile
Next, edit the /etc/fstab file and remove the following line:
nano /etc/fstab
Remove the following line:
/swapfile swap swap defaults 0 0
Next, remove the swap file using the following command:
rm -rf /swapfile
Next, verify whether the swap space is removed or not with the following command:
swapon --show
Conclusion
In the above guide, you learned how to check and create a swap space on Linux. You also learned how to monitor the swap space with different commands. Get started today with your VPS from Atlantic.Net.
