Swap, Memory and Swap File

Swap and memory

One important setting in any protected mode operating system like Linux is the swap space. In the installation, you will need to create a swap partition. 

A common question is what size should the partition be?

The proper size depends on 2 things: The size of your hard drive and the size of your RAM memory. The less RAM you have, the more swap you will need. Usually you will want to set your swap space size to be twice the RAM size, with a maximum of 128 megs. This of course requires you to have a hard drive with enough free space to create such a partition.

If you have 16 megs of RAM, making the swap space 32 megs or even 64 megs is very important. You will need it. If you have 128 megs of RAM on the other hand, you won't need much swap because the system will already have 128 megs to fill before using swap space. So a swap partition of 128 megs or even 32 megs could be enough.

If you don't select enough swap, you may add more later.

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More swap with a swap file

You installed a new Linux system, but forgot to set enough swap space for your needs. Do you need to repartition and reinstall? 

No, the swap utilities on Linux allow you to make a real file and use it as swap space.

The trick is to make a file and then tell the swapon program to use it. Here's how to create, for example, a 64 megs swap file on your root partition (of course make sure you have at least 64 megs free):

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

This will make a 64 megs (about 67 millions bytes) file on your hard drive. You now need to initialize it:

mkswap /swapfile 65536

sync

And you can then add it to your swap pool:

swapon /swapfile

With that you have 64 megs of swap added. Don't forget to add the swapon command to your startup files so the command will be repeated at each reboot.

Linux Tips

See Also
How To Make Linux Bootable Disk

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