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.

which
command. which is usually used to locate a program quickly.
It just searches your PATH and returns the first instance it finds and the directory path
to it. Take this example:
% which bash
/bin/bash
From that you see that bash is in the ��+ directory. This is a very limited command
for searching, since it only searches your PATH.
whereis
A whereis search for bash should return this:
% whereis bash
bash: /bin/bash /usr/bin/bash /usr/man/man1/bash.1.gz
This command not only told us where the actual program is located, but also where
the online documentation is stored.
find
The find(1) command allows the user to search the filesystem with a rich collection
of search predicates. Users may specify a search with filename wildcards, ranges of
modification or creation times, or other advanced properties. For example, to search
for the default = file on the system, the following command could be used.
% find / -name xinitrc
/var/X11R6/lib/xinit/xinitrc
find will take a while to run, since it has to traverse the entire root directory tree.
And if this command is run as a normal user, there will be permission denied error
messages for directories that only root can see. But find found our file, so that’s
good. It pretty slow.
slocate
The slocate(1) command searches the entire filesystem, just like the find command
can do, but it searches a database instead of the actual filesystem. The database is set
to automatically update every morning, so you have a somewhat fresh listing of files
on your system. You can manually run updatedb(1) to update the slocate database
(before running updatedb by hand, you must first su to the root user).
example of slocate in action:
% slocate xinitrc # we don’t have to go to the root
/var/X11R6/lib/xinit/xinitrc
/var/X11R6/lib/xinit/xinitrc.fvwm2
/var/X11R6/lib/xinit/xinitrc.openwin
/var/X11R6/lib/xinit/xinitrc.twm
With these commands,
you should be able to find whatever you’re looking for on your Linux system.