Installing software error: no installation candidate

Question

I want to install the software doxygen and graphvi for my research. I used the command

sudo apt-get install doxygen graphviz

then it is returning these errors:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package graphviz is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Unable to locate package doxygen
E: Package 'graphviz' has no installation candidate

How can i fix this? thanks in advance

Answer 1

This happens when you are trying to install a package about which apt does not have any idea.

The packages that you are trying to install can be found in Ubuntu Software Center: doxygen-gui and graphviz. So, possible reasons for receiving these errors can be:

• Your version of Ubuntu is "end of life" in which case you should follow this post
• You don't receive packages for some repository components (I think main or universe). See how you can change repositories in Ubuntu here: https://help.ubuntu.com/community/Repositories/Ubuntu.

Answer 2

The error that you're getting could be as Radu Rădeanu stated in his answer, and could also be that the command that you used is not correct. Now if you are using any Ubuntu release prior to 12.04LTS, with the exception of 10.04LTS, then your release has reached end-of-life. If that is not the case, then:

To install Doxygen, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

sudo apt-get install doxygen-gui

Or click Doxygen

As far as Graphviz, to install click Graphviz .