Type the command:
# whereis <program>
where program is the program you are looking for, will show you one or more possibilities for what you are looking for.
If you have more than one copy of a program, say one in /usr/bin and another in /usr/local/bin/ ,
typing "which program" will show you which one will be called first.
If you can't find it at all, type command:
# locate <program>
will show you everyfile that matches "program".
Some of the most common programs :
Default locations for most commonly used configuration files and important directories: