Add a swap file or expand existing swap space

It’s a myth to say that Ubuntu (or any Linux) needs a swap partition.
This is certainly the preferred way of working, and is most efficient,
but Linux can also use a single swap file located in the root partition,
just like Windows or Mac OS X. There are times when this is advan-
tageous, such as if you’re only able to create one partition for Ubuntu
(for example, Apple’s BootCamp software only allows the creation of a
single non-Mac partition when dual-booting).
To create a swap file, you need to first create a dummy file of sufficient
size, then format it as a swap file, and finally ensure that Ubuntu uses
it at boot-up. The following steps do just that (be extremely careful
entering these commands):
1. Open a terminal window and create an empty file in the root of the
file system using the dd command, as follows (this creates a 1GB
file—you should ideally adjust the count= figure to at least match
the size of your memory, bearing in mind that there is 1,024MB in
a 1GB):

$ sudo dd if=/dev/zero of=/swapfile bs=1M count=1024

2. Now we need to format it as a swap file:

$ sudo mkswap /swapfile

3. The final step is to make Ubuntu mount it at boot, which is done
by editing /etc/fstab:

$ gksu gedit /etc/fstab

Then make a new line at the bottom of the file and add the follow-
ing:

/swapfile none swap sw 0 0

You can align the entries on the line under the column headings
in fstab, like the other entries in the file, but it doesn’t matter so
long as there is at least one space between each entry on the line.
Once done, save the file and reboot your computer.
Once the computer has rebooted, you can test to see if the swapfile is
being utilized by typing cat /proc/meminfo|grep Swap.
The steps above can also be used to add more swap space to a system
that has an existing swap partition. You might want to do this if you’re
editing extremely high-resolution photographs, for example, or working
with large video files.