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In the ~ directory of the root user on my debian wheezy server regularly appears file named dead.letter with (currently) the following content:

orion : Jul 25 10:17:31 : root : unable to resolve host orion orion : Jul 26 02:17:18 : root : unable to resolve host orion orion : Jul 26 21:17:19 : root : unable to resolve host orion

orion is the hostname of the server (and can normally be resolved since I have various services/programs using this hostname without problems). After some searching I figured that there is a cron job running hourly, i.e.

17 * * * * root cd / && run-parts --report /etc/cron.hourly

which could explain why those errors only appear 17 minutes after the full hour. The only script in /etc/cron.hourly is fake-hwclock with the following content:

#!/bin/sh # # Simple cron script - save the current clock periodically in case of # a power failure or other crash if (command -v fake-hwclock >/dev/null 2>&1) ; then fake-hwclock save fi

Can this produce those mysterious dead.letter? And why seems fake-hwclock save try to resolve the hostname?

Edit: Some more information.

Input of /etc/hosts:

127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters
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  • /etc/hosts is a starter. Commented Jul 27, 2015 at 11:22
  • See edited post. What do I have to look for in /etc/hosts? Commented Jul 27, 2015 at 11:26

2 Answers 2

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Change the following line in /etc/hosts

127.0.0.1 localhost

to

127.0.0.1 localhost orion

Your MTA was unable to resolve the domain name of your machine.

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  • I think I have to wait some time to ensure this is the correct answer. But it does make sense to me. Will eventually later mark your answer as correct. Commented Jul 27, 2015 at 11:43
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    Some context/explanation would be helpful. Why do these messages appear in dead.letter rather than some log, for example? Commented Jul 27, 2015 at 11:46
  • @FaheemMitha see the answer below. Jodkas answer solved the problem for me, but Gerhards answer explains the "why" more detailed. Commented Jul 27, 2015 at 15:24
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Jodka Lemon's answer is correct:

  • cron executes its job, and sends a result mail to "root@orion" (via "mail" or similar)
  • the MTA cannot resolve host orion, since the hostname is not listed in /etc/hosts and not resolvable via dns.
  • so the mailer writes the dead letter information

You will find the destination address of crons mail output in the crontab file which holds the /etc/cron.hourly entry. This sould be /etc/crontab, I think...

Have Fun ... Gerhard

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