How do I add a swap file?

Seth provided a really good answer :) keep up the good work. But I
would say that you only really need swap if your ram is less than say
1 gig. otherwise the swap won't do you much good :)

On Wed, Feb 17, 2010 at 6:40 AM, Seth Arnold
<email address hidden> wrote:
> Question #101400 on Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+question/101400
>
>    Status: Open => Answered
>
> Seth Arnold proposed the following answer:
> (1) create the swap file with dd if=/dev/zero of=/path/to/swapfile bs=4096 count=$((256*<size in megabytes>))
> (2) mark the file as a swapfile with mkswap /path/to/swapfile
> (3) add the file to /etc/fstab (optional, if you want it on after rebooting..)
> (4) swapon -a (if you edited fstab) or swapon /path/to/swapfile
>
> There's nothing magic about the bs and count options to dd. Make sure
> that when you multiply them together, you get the size of the file you
> want. (Feel free to check it with ls -l.) But note that setting bs too
> small will take a long time, and setting it too large might put a lot of
> memory pressure on the system. (I wouldn't recommend trying to write out
> a whole gigabyte at once. :) I find it easy to think in kilobytes, so I
> often use 1024, but I imagine you'll want to add gigabytes of swap, and
> working in whole pages is usually more efficient.
>
> --
> You received this question notification because you are an answer
> contact for Ubuntu.
>

--
Regards,
Vikram Dhillon

~~~
There are lots of Linux users who don't care how the kernel works, but
only want to use it. That is a tribute to how good Linux is.
-- Linus Torvalds

Seth, thanks.
I would like to add, that for adding the swap file to fstab, you need to add this line:
/swap/swapfile.swap none swap sw 0 1

Vikram, some people need more than one gig of RAM. I wanted swap, because I experienced out of memory events (oom-killer).

Thanks Seth Arnold, that solved my question.