Detect if root login is disabled?

[Daniel Hartwig <mandyke@gmail.com>]

Hello

I am looking at Bug#516854 and wondering:

Is there a robust way for a *user* to detect if root login is
disabled?  Would like to perform such a check from an instance of
aptitude running as a user account.

I am aware of the following method which detects the `passwd -l' style
lock, however, it requires read access to /etc/shadow:

io:~# passwd -S root | grep " L " > /dev/null; echo $?
1
io:~# passwd -l root
passwd: password expiry information changed.
io:~# passwd -S root | grep " L " > /dev/null; echo $?
0

Thanks