Add swap partitions in Linux

Linux Add a swap file-howto

By nixcraft on
May 18,200 6· 34 comments · last updated
January 4, 2012.

I need additional swap space to improve my system performance. How do I add a swap file to Linux System Using command line options?

In Linux, as in most other UNIX-like operating systems, it is common to use a whole partition of a hard disk for swapping. however, with the 2.6 Linux kernel, swap files are just as fast as swap partitions, although I recommends using a swap partition. the
Administrative flexibility of swap files outweighs that of partitions; since modern high capacity hard drives can remap physical sectors, no partition is guaranteed to be contiguous. you can add swap file as a dedicated partition or use following instructions
To create a swap file.

Procedure to add a swap file under Linux

You need to use the DD command to create swap file. The mkswap command is used to set up a Linux swap area on a device or in a file.

Step #1: Login as the root user

Open a terminal window (select applications> accessories> terminal) or login to remote server using the SSH client. Switch to the root user by typing Su-and entering the root password, when prompted

Step #2: Create storage file

Type the following command to create 512 MB swap file (1024*512 MB = 524288 block size ):
# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
Where,

1. If =/dev/zero: Read from/dev/Zero file./dev/zero is a special file in that provides as your null characters to build storage file called/swapfile1.
2. Of =/swapfile1: Read from/dev/Zero write stoage file to/swapfile1.
3. BS = 1024: Read and Write 1024 bytes at a time.
4. Count = 524288: Copy only 523288 blocks input blocks.

Step #3: Set up a Linux swap area

Type the following command to set up a Linux swap area in a file:
# mkswap /swapfile1
Setup correct File Permission for security reasons, enter:
# chown root:root /swapfile1
# chmod 0600 /swapfile1
A world-readable swap file is a huge local vulnerability. The above command make sure only root user can read/write to the file. Finally, activate/swapfile1 swap space immediately, enter:
# swapon /swapfile1

To activate/swapfile1 after Linux system reboot, add entry to/etc/fstab file. Open this file using a text editor such as VI:
# vi /etc/fstab

Append the following line:
/swapfile1 swap swap defaults 0 0
Save and close the file. Next time Linux comes up After reboot, it enables the new swap file for you automatically.

How do I verify swap is activated or not?

Simply use the free command:
$ free -m

See also:

• Linux display system hardware status information gathered from/proc filesystem in easy format (supported des swap info)

Page last updated at, January 5, 2012.

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Http://www.cyberciti.biz/faq/linux-add-a-swap-file-howto/