How do I add swap using a filesystem file to my Red Hat Enterprise Linux system?

Environment

• Red Hat Enterprise Linux all version

Issue

• How do I add a swap file to my Red Hat Enterprise Linux system?
• Need help in increasing swap space.
• How to increase swap space.

• Exceptions:
• For creating swap space using a device:
• Follow the directions in: "How to create/add swap space using a storage device"

Resolution

1. Determine the size of the new swap file in megabytes and multiple by 1024 to determine the block size. For example, the block size of a 64 MB swap file is 65536.

2. At a shell prompt as root, type the following command with count being equal to the desired block size:

   # dd if=/dev/zero of=/swapfile bs=1024 count=65536
   

3. Change the permissions to readable and writeable only by root:

   # chmod 600 /swapfile 
   

4. Setup the swap file with the command:

   # mkswap /swapfile
   

5. To enable the swap file immediately but not automatically at boot time:

   # swapon /swapfile
   

6. To enable it at boot time, edit /etc/fstab to include:

   /swapfile    swap    swap   defaults 0 0
   

   New swap file will be enabled after next system boot.

7. After adding the new swap file and enabling it, verify it is enabled by viewing the output of the command cat /proc/swaps or free.

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