How to create a swap on Ubuntu 14.04

What is a Swap Partition ?

A linux swap partition becomes useful when your server’s RAM gets full. When your RAM gets full, then your swap partition will act as a RAM for your other applications. But does not this mean this is a great alternative to having a large RAM, because a swap partition on a hard drive (even SSD) can never be as fast as a RAM from a hardware point of view.

Step 1 : Check for any existing SWAP on the server by running the following command

sudo swapon -s

If you get the following output, that means you DO NOT have any swap space allocated as of now

Filename                Type        Size    Used    Priority

You may also check for swaps on the server using

free -m

Should show Swap values as zero :

             total       used       free     shared    buffers     cached
Mem:          3998       1483       2515         64         93       1089
-/+ buffers/cache:        300       3698
Swap:          0          0        0

Step 2 : Once we have established that there are no existing swaps on the server, we will then check for the available space on the server

df -h

This will show the server disk usage in the following format :

Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda        89G  1.9G   86G   3% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
devtmpfs        2.0G  4.0K  2.0G   1% /dev
none            400M  212K  400M   1% /run
none            5.0M     0  5.0M   0% /run/lock

Step 3 : Once we have established that there is sufficient space on the server disk to create a swap, we will create our swap file, in the root directory.

cd /
sudo dd if=/dev/zero of=/swapblock bs=256M count=4

The above mentioned ‘dd’ command will specify 4 blocks each of size of 256 Megabyte. Totalling to a swap size of 1 GB. It should provide an output in the following format

4+0 records in
4+0 records out
1294728296 bytes (1.3 GB) copied, 6.6227 s, 231 MB/s

To check that the swap has been allocated correctly, execute the following command

ls -lh /swapblock 

This should display the swap block with it’s size

Step 4 : Now the swapblock is created and the space has been allocated on the server, but the system does not know what to do with the space allocated yet. To solve this we will enable the swap on your ubuntu 14.04 server.

sudo mkswap /swapblock 

This command will set up the swap space on the ubuntu server. It should display an output of the format

Setting up swapspace version 1, size = 1194300 KiB

Once the swap space is set up, we will then enable it

sudo swapon /swapblock 

This will enable the swap file on your Ubuntu 14.04 server.

Step 5 : Check that the Swap file is enabled on the server

sudo swapon -s

This should display an output like

Filename                Type        Size    Used    Priority
/swapblock              file        1194300 0       -1

Step 6 : Once we have confirmed that the swap file is setup and enabled, we then need to make the swap permanent on the server, so that we do not loose the changes if the server is reboot or restarted.

Open the fstab file using your favourite editor. We will use nano for this example.

sudo nano /etc/fstab

and add the following line at the bottom of this file

/swapblock  none    swap    sw    0   0