$locate .ini

Locate all the ini files on the system

$which php

Find out where the command is being run from (in this case "php").  This is useful if a program isn't responding as you expect - perhaps because the wrong version is being called.

$whereis php

Extending on which php - this tells you if there are any other commands that are on the system with the same name.  If the program isn't responding as expected, then if could be that one of these should be called instead.

If you aren't sure about a command, you can either use

$man command

or

$command --help

as one of these might help you with the parameters expected.

Lastly, there is another command that I use, that isn't necessarily obvious called grep.  This is used to filter lines of output, so if you have something that's outputting loads of lines to the console, and you can't find the line you need, this might help.

Here is an example:

$locate .ini | grep opera

This will list all of the ini files, including the paths, which contain the text "opera".  In this case, it's a way of finding configuration files for the Opera web browser, but once you get the ides, there are tonnes of things that you can do with it.  You can even fine-tune the filtering, like:

$locate .ini | grep opera | grep standard

This will show all the lines of output that contain "opera" and "standard" - but not one or the other.

There are more sophisticated and flexible approaches, but I find this useful for day-to-day stuff.

If me, you weren't sure about how Linux's file system works, here is a fantastic overview of it:

http://www.tuxfiles.org/linuxhelp/linuxdir.html