Creating SWAP partition using FDISK & FALLOCATE commands

Swap-partition holds the memory which is used in case the physical memory (RAM) is full . When RAM capacity has been utilized to maximum , 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 as a replacement to physical memory/RAM.

In most cases, it is advised to keep SWAP-memory equal to size of physical memory at minimum & double the size of physical memory at maximum. So if you have 8 GB RAM on your system, 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 Linux system & we will be discussing two methods for creating a swap-partition

  • Using fdisk command
  • Using fallocate command

First Method (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 default value & then you will asked to enter last cylinder value, here we will enter the size of swap partition (we will be using 1000MB). Enter the value in last cylinder as +1000M.


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 asked to enter  partition id which for swap it’s 82 (to see 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.


Second Method (using fallocate command)

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

To create a swap using fallocate, we will firstly 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

Now only root will be able to read, 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.


This completes our tutorial, I hope it was simple enough to understand & learn. If you are having any issues or have have any queries, please mention them in the comment box below.

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2 Responses

  1. mmiat says:

    in fstab the option is default or defaults ?

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