CreateSwapFile

How to Create and Enable a Swap File in Linux

1. In this example, we will create a swap file of size 2GB using the dd command as follows. 
Note that bs=1024 means read and write up to 1024 bytes at a time and count = (1024 x 2048)MB size of the file.

logon as root

# dd if=/dev/zero of=/mnt/swapfile bs=1024 count=2097152

Alternatively, use the fallocate command as follows.

# fallocate --length 2GiB /mnt/swapfile

And then set the appropriate permissions on the file; make it readable only by root user as follows.

# chmod 600 /mnt/swapfile

2. Now setup the file for swap space with the mkswap command.

# mkswap /mnt/swapfile

3. Next, enable the swap file and add it to the system as a swap file.

# swapon /mnt/swapfile

4. Afterwards, enable the swap file to be mounted at boot time. 
Edit the /etc/fstab file and add the following line in it.

/mnt/swapfile swap swap defaults 0 0

In the line above, each field means:

/mnt/swapfile – device/file name
swap – defines device mount point
swap – specifies the file-system type
defaults – describes the mount options
0 – specifies the option to be used by the dump program
0 – specifies the fsck command option

6. To set how often the swap file can be used by the kernel, 
open the /etc/sysctl.conf file and add the line below.

vm.swappiness=10

Note that the default value of how frequent swap space can be used is 60 (maximum value is 100). 
The higher the number, the more frequent swap space utilization by the kernel. 
When the value is set to 0, the swap file will only be used if the operating system has fully utilized memory.

6. Now verify the swap file was created using the swapon command.

# swapon  -s

# Your new swap file will be active after each reboot.