What is Swap Partition and how to create it on Linux

Swap-partition holds the memory which is used in case the physical memory (RAM) is full. When RAM capacity has been utilized to maximum, the Linux machine moves inactive pages from memory to swap-space which are then used by the system. Though it gets the work done, it should not be considered a replacement for physical memory/RAM.

Similiar: What is Partition, Type, and how to create a normal partition

Creating SWAP partition using FDISK & FALLOCATE commands

In most cases, it is advised to keep SWAP memory equal to the size of physical memory at minimum & double the size of physical memory at maximum. So if you have 8 GB RAM on your system, the Swap should be between 8-16 GB.

If a swap partition has not been configured in your Linux system, your system might start killing off the running process/applications & might cause your system to crash. In this tutorial, we will learn to add swap-partition to a Linux system & we will be discussing two methods for creating a swap partition

• Using fdisk command
• Using fallocate command

Creating swap Using Fdisk command

Normally, first hdd of the system is named /dev/sda& partitions for it are named /dev/sda1 , /dev/sda2. For this tutorial we will using a HDD that have 2 primary partitions on system i.e. /dev/sda1, /dev/sda2 & SWAP will be /dev/sda3.

Firstly we will create a partition,

$ fdisk /dev/sda

to create a new partition type ’n’. You will now be asked to enter the first cylinder value, just hit enter key to use the default value & then you will be asked to enter the last cylinder value, here we will enter the size of the swap partition (we will be using 1000MB). Enter the value in the last cylinder as +1000M.

Similar: Linux User & Group Management

We have now created a partition of size 1000MB but we have not assigned it any partition type, so to assign a partition type, press “t” & press enter.

Now you will be first asked to enter partition number, which is 3 for our partition & then we will ask you to enter partition id which for swap it’s 82 (to see a list of all available partition types, press “l” ) & then press “w” to save the partition table.

Next, we will format our swap partition  using mkswap command

$ mkswap /dev/sda3

& will then activate our newly created swap

$ swapon /dev/sda3

But our swap will not be mounted automatically after every reboot. To mount it permanently in our system, we need to append /etc/fstab file. Open /etc/fstab file & make an entry of the following line

$ vi /etc/fstab
/dev/sda3             swap            swap            default          0   0

Save & close the file. Our swap now will even work after a reboot.

Creating swap using fallocate command

I prefer this method as this is the easiest & fastest way to create a swap. Fallocate is one of the most underestimated & very less used commands. fallocate is used to pre-allocate blocks/sizes to a file.

To create a swap using fallocate, we will first create a file named swap_space in ‘/’.  Next, we will allocate 2GB to our file swap_space,

$ fallocate –l 2G /swap_space

We will then verify the size of the file by running

ls-lh /swap_space.

Next, we will make our /swap_space more secure by changing the file permissions

$ chmod 600 /swap_space

Similar: Linux File & Directory Permission

Now only the root will be able to read and write on this file. We will now format the swap partition,

$ mkswap /swap_space

& then will turn on our swap

$ swapon -s

This swap partition will need to be remounted after every reboot. So to make it permanent, edit the /etc/fstab, as we did above & enter the following line

/swap_space      swap        swap          sw          0   0

Save & exit the file. Our swap will now be permanently mounted. We can check if your swap is working or not by running “free -m” on your terminal after rebooting the system.