Unable to locate package in Ubuntu while trying to install packages by apt

First, check if the package actually exists:

1. Go to packages.ubuntu.com with a web browser.
2. Scroll down to "Search package directories"
3. Enter the package which you're trying to install into the "Keyword" field.
   Enable "Only show exact matches:"
   Change the "Distribution" to which version of Ubuntu you're using.

   

If there are no results, the package you are looking for doesn't exist and the next steps will not work. It may require a third party PPA or an alternative installation method.

If results are found, the package exists and you may continue with these steps:

1. Open Software Sources (or Software & Updates in 13.04+) by searching for it in the Dash.
2. Open the "Ubuntu Software" tab.
3. Ensure that the first 4 check boxes on this tab are enabled:
   
4. Update the package lists, then test with these commands:

   sudo apt-get update
   sudo apt-get install <TEST_PACKAGE>
   
   

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