I know that crontab -r removes the user's crontab, but what's more likely (based on your content) is that a new version of cron was installed -- and that process somehow overwrote the existing crontab with what looks like a default version.

I have a line in my crontab that does a periodic save:

#  2018-1121: 1533: Save the current crontab for later backup
36   8,15   *   *   *   crontab -l >/home/web/crontab.latest

I then use rsync to back that file (and others) up to a safe place.

Alex

On Wed, Jan 9, 2019 at 11:45 AM Darryl Moore via talk <talk@gtalug.org> wrote:
so I have about 100 servers running 16.04 spread over North America.

Today it became apparent that the root user cron script was deleted on
all 100 of them. The script is at /var/spool/cron/crontab/root and
everything I had has been deleted and replaced with

# DO NOT EDIT THIS FILE - edit the master and reinstall.
# (- installed on Fri Dec 28 08:18:31 2018)
# (Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)

crontabs were all originally installed using the crontab executable.
when I redo it the same way I get the proper crontab file but with this
above header added. This was never the case before. I do not have
automatic updates turned on on any of my machines. The date stamp in
this header is within a few seconds of the above on all my machines. I
also have a few machines running Armbian, and they are exactly the same.

This is a major F*up for me and I have no idea how it happened. Has
anybody else had similar experiences? I'd love to know.

regards,
darryl
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--
Alex Beamish

Speaker Wrangler / Toronto Perlmongers / http://to.pm.org/
Baritone, Operations Manager / Toronto Northern Lights, 2013 Champions / www.northernlightschorus.com
Certified Contest Administrator / Barbershop Harmony Society / www.barbershop.org