Allocate swap after Ubuntu 14.04 LTS installation

First, to create 4,000 MB of swap space:

$ sudo dd if=/dev/zero of=/swapspace bs=1M count=4000
4000+0 records in
4000+0 records out
4194304000 bytes (4.2 GB) copied, 5.92647 s, 708 MB/s

or

$ sudo fallocate -l 4000M /swapspace 

Next turn it into a usable swap file:

$ sudo mkswap /swapspace
Setting up swapspace version 1, size = 4095996 KiB
no label, UUID=7d1895e4-7ccf-42c6-979a-51ebddb49e91

Activate it:

$ sudo swapon /swapspace 

Confirm active swap spaces:

$ cat /proc/swaps
Filename                Type        Size    Used    Priority
/swapspace              file        4095996 0       -1

Next, add the following line to /etc/fstab to activate the new swap at boot:

/swapspace none swap defaults 0 0

See also this wiki page: https://help.ubuntu.com/community/SwapFaq

To answer your question indirectly, you don't need to manage swapfiles yourself. There is a package called swapspace which will dynamically add swap files as needed.

1. sudo apt-get install swapspace

Then you are done. Your system will grow and shrink swap space as needed.

Follow these steps:

1. sudo dd if=/dev/zero of=/mnt/{filename}.swap bs=1M count={swap_size}
2. sudo mkswap /mnt/{filename}.swap
3. sudo swapon /mnt/{filename}.swap
4. sudo gedit /etc/fstab
5. Add the following text at the end of the file, /mnt/{filename}.swap none swap sw 0 0

Note: Replace {filename} with any name you want to set to the file and replace {swap_size} with the size you want to assign to the swap file. Be sure the size of the file must the twice larger than the memory size.