Hello guys, after wasting an hour to find a way to set the static IP address in my machine, I figured out the cause of the problem. If you've read 'Setting up static address' in ubuntu server documentation, you know that you can do that by writing stuff to a file. However, it will not work in Desktop Edition of Ubuntu, because there is an application called 'network-manager' that keeps the same configurations and prevents the written configurations to be applied for static addressing.
So, in order to set a static IP address, you need to enter your details into that program. Usually, you will find it in settings and it's (usually) named Network Connections.
After finding the application, you should be able to see a list of ethernet interfaces (including wifi) and double-click on appropriate one or select one and press 'Edit'.
Once you've done that, you will see property tabs. Click on 'IPv4 Settings'
You should see a drop down list next to 'Method:' and select 'Manual'. Then you will notice that you will be able to add an address to the list. Enter appropriate settings. Remember that Gateway is a point where you can access the internet (e.g router) and Netmask is the one that usually facemask of IP addresses. Usually it looks like 255.255.255.0, but you have to check it yourself. Furthermore, DNS server is usually the same as Gateway address if you have a home router.
Once information is entered, save it and restart the computer. Now your computer should have the static IP address.
Note: Since I showed this example in Lubuntu, you should be able to find the same or similar settings on different variants of ubuntu.
