Swap in Linux is an entirely different beast from the /tmp. While Solaris or SunOS treats /tmp and swap as one. Adding swap can be done in two ways: [1] adding swap from a free partition; or [2] adding swap from a file. In this how-to, we will add swap from a file. How is this done?
In order to see the swap space and its usage, use "swapon -s" or "cat /proc/swaps" to get more information. The output will be somewhat similar to this:
Filename Type Size Used Priority
/dev/sda1 partition 859436 0 -1
To add swap, follow the directions below:
1. Determine the size of the new swap file 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:
==> 64MB
root@host # dd if=/dev/zero of=/PATH/swapfile bs=1024 count=65536
==> 512MB
root@host # dd if=/dev/zero of=/PATH/swapfile bs=1024 count=524288
==> 1GB
root@host # dd if=/dev/zero of=/PATH/swapfile bs=1024 count=1048576
3. Setup the swap file with the command:
root@host # mkswap /PATH/swapfile
4. To enable the swap file immediately (but not automatically at boot time):
root@host # swapon /PATH/swapfile
After adding the new swap file and enabling it, make sure it is enabled by viewing the output of the command "cat /proc/swaps" or free.
To permanently enable the swap file at boot time, edit /etc/fstab to include below line:
/dev/sda1 swap swap defaults 0 0
