Dia is an unsupported program on the Linux system at Chalmers. So it's likely that you will not have access to dia (and other unsupported software on the Linux system at Chalmers) by default, and you will get the message "dia: command not found" when you type "dia".
A simple solution is to give the full pathname for the command:
/chalmers/sw/unsup64/phc/b/binl/dia
Alternatively, read the following notes if you want to use dia (and other unsupported software on the Linux system at Chalmers) in a more convenient way. This approach has the advantage that you will also be able to access the manual pages for dia ("man dia") and other unsupported programs.
In order to use unsupported programs, you must have a line with "unsup" in your $HOME/.vcs4/pathsetup file. If you don't have this line in your $HOME/.vcs4/pathsetup file (or you don't have a $HOME/.vcs4/pathsetup file), you can add the line (and create the file, if necessary) by running the following command:
echo unsup >> $HOME/.vcs4/pathsetup
You only need to run this command once.
It might be necessary to start a new shell before the unsupported programs are available.
See: Unsupported software