Managing cron and similar E-Mails from headless systems

[Gene Heskett]

On Friday 17 February 2017 11:15:39 Chris Green wrote:

> On Fri, Feb 17, 2017 at 11:00:16AM -0500, Gene Heskett wrote:
> > On Friday 17 February 2017 06:14:01 Chris Green wrote:
> > > I have several headless systems doing useful work around the
> > > place:-
> > >
> > >     A Raspberry Pi providing local DNS and DHCP
> > >
> > >     A Beaglebone Black on our boat monitoring temperatures and
> > > batteries
> > >
> > >     An old desktop doing backups in the garage
> > >
> > >     etc.
> > >
> > >
> > > Most of these have one or more cron jobs running periodic rsync
> > > backups, copying data, etc.  If the cron job has an error then it
> > > sends E-Mail to the owner of the job ('chris' in most cases, might
> > > be root in a couple).
> > >
> > > It's (moderately) easy to set up an MTA and /etc/aliases so that
> > > the messages are sent to my normal E-Mail.  However I can't come
> > > up with a straightforward way of indicating where the messsage is
> > > *from*.
> > >
> > > You can't just invent a domain name for the headless system
> > > because that gets the E-Mail rejected by intermediate systems that
> > > try and look up the sender host name.  Cron doesn't seem to have
> > > any mechanism for setting the sender's name, cron errors just come
> > > from 'root@'.
> > >
> > > Can anyone suggest a neat way of handling this so that I know
> > > where the errors are coming from?
> > >
> > > --
> > > Chris Green
> >
> > A hosts file based home network should suffice to fix that. I did
> > have it setup to do that from 3 of the now 5 machines here, but the
> > inability to separate the messages into important turned the whole
> > thing into spam for me. Set your resolv.conf to include the
> > commands:
> > "nameserver local.address.of.router"
> > and:
> > "order hosts,dns"
> >
> > So it will look at /etc/hosts first, failing to find a match there
> > it sends it to the router, which forwards it to your ISP's dns.
> >
> > 1. Set the hostname and domain name of your machines so they know
> > who they are.
> >
> > 2. run the same hosts file on all machines, which lists the local
> > ip, names, and aliases of the whole local network, 7 lines here plus
> > the obligatory localhost stuff, does it nicely.  Then on the client
>
> Erk, I've spent the last N years avoiding maintaining lots of hosts
> files on my home LAN.  I run dnsmasq on a raspberry pi to do it all
> for me automatically.
>
> > machines, I just set the MailTo: gene at coyote, and it magically
> > appears in my /var/spool/mail/gene queue. That in turn triggers a
> > watcher script to send kmail a getmail message over whatever message
> > bus your system uses, dbus here ATM, to go get the mail.
> >
> > But unless you can make procmail (I use a fetchmail->procmail
> > processing chain here) send the unimportant stuff to /dev/null,
> > you'll likely tear it back down in a week or 2. You don't need to
> > know, when logging into one of the other machines, everytime you fat
> > fingered the password. With my short fat fingers, and 82 years of
> > arthritis accumulated, very easily done.
>
> I don't use any sort of mail fetcher, mail is delivered to my home
> machine (which is on all the time) by SMTP.
>
Whereas all my stuff is behind a dd-wrt NATing router, so except for my 
web page, invisible to the rest of the world.

> --
> Chris Green


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>