`apropos` is not to find "forgotten (or unknown!) commands", but rather a manual page relating to a specific subject. On my machine, `tzconfig` doesn't have a manual page (it's nothing more than a shell script), so nothing will show up.

But why not use `locate` with a grep on bin? In this specific example (tzconfig), that helped me more than this perl snippet, since "/usr/sbin" is not in my $PATH.

$ locate tzconfig | grep bin
/usr/sbin/tzconfig
[download]

Or if you know you've recently used the command, `history` will guide you, and if you know the first n letters of your command, and the application is in your path, a double [Tab] will do just fine :)

# tz[Tab][Tab]
tzconfig tzselect
# tz
[download]