[Popcon-developers] Bug#668784: "su: Authentication failure\n(Ignored)" error message when from cron job

[Raf Czlonka]

On Sat, Apr 14, 2012 at 08:35:17PM BST, Bill Allombert wrote:
> Hello Raf,

Hi Bill,

Thanks for a quick response.

> Do you know why 'su' complains ?

Initially I didn't and since it was the only occurrence I've seen on my
system I assumed it was caused by popularity-contest itself.

> Does 
> su -s /bin/sh -c /usr/sbin/popularity-contest nobody
> fail ?

Well, it generates that error message but it seems like it works.

> Does
> su -s /bin/sh -c /bin/ls nobody
> work ?

It was with the error message but did work.

Eventually I tracked it down - well, I think so anyway ;^)
I've managed to get rid of the message at least, and probably its
original cause.

Adding user "nobody" to /etc/shadow file fixed the issue.

It's hard for me to establish whether it has ever been there in the
first place, and if so, when has it been removed and by which package.
I keep my /etc in git repository using etckeeper but it seems that if
anything has changed /etc/{passwd,shadow,group,gshadow} it must have
been before I started using etckeeper as history doesn't show anything.

Since /etc/shadow and /etc/gshadow are generated using "shadowconfig",
actually by "pwconv" and "grpconv" respectively, user "nobody" exists
in the original "passwd.master" file from "base-passwd" package and it
gets created by running "update-passwd" and "pwconv" in chroot
environment, it sounds like what I've written above is true and there's
a broke bit of software somewhere [0] which removes that user.

[0] Not necessarily an official Debian package from debian.org
repository but from another one (I use quite a few) or an unpackaged
bit of software.

Ta,
-- 
Raf