How to Create Swap File in Linux

 How to Create Swap File in Linux

Create a 8GB file.
[root@exampleserver ~]# dd if=/dev/zero of=/swap8gfile bs=1G count=8
8+0 records in
8+0 records out
8589934592 bytes (8.6 GB) copied, 7.57026 s, 1.1 GB/s
[root@exampleserver ~]#

Change the swapfile Permission
[root@exampleserver ~]# chmod 644 /swap8gfile

Enable the Swap area.
[root@exampleserver ~]# mkswap /swap8gfile
mkswap: /swap8gfile: warning: don't erase bootbits sectors
        on whole disk. Use -f to force.
Setting up swapspace version 1, size = 8388604 KiB
no label, UUID=008a5d0f-5b73-4aec-b209-8c283553ad33
[root@exampleserver ~]#

You can add the the entry in fstab, so the swap can be persistent across reboots.
/swap8gfile swap                    swap    defaults        0 0

Now Enable the swap.
[root@exampleserver ~]# swapon /swap8gfile
[root@exampleserver ~]# free -m
             total       used       free     shared    buffers     cached
Mem:        515671      11721     503949          0         45       8403
-/+ buffers/cache:       3272     512398
Swap:        24575          0      24575
[root@exampleserver ~]#

Few Handy Commands:

free -g --check the current swap status

swapoff swapfile -- Off the swap space if already created. It is not required if creating a new one

 rm swapfile -- Remove Swap file
 dd if=/dev/zero of=/opt/swapfile bs=1024 count=4553600 -- Create a swap file of 4.7 GB
 chmod 0600 /opt/swapfile -- Change the Permission of SwapFile
 mkswap /opt/swapfile --- Define the swapfile as swap space
 swapon /opt/swapfile --- switch on the swap space so that it can be used by system
  free -g --check the current swap status
/opt/swapfile               swap                    swap    defaults        0 0 -- Now Make an entry in fstab file