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I have several cron jobs that run (in /etc/cron.daily, /etc/cron.hourly, /etc/cron.weekly, etc.) and email root@localhost with the results. I'd like to stop those emails if the jobs are succeeding, and only email on error (which I understand can be done by redirecting stdout to /dev/null). I understand how to do that for individual cron jobs, but the scripts in those special directories are run using run-parts. What is the best way to suppress success emails for those scripts?

jrdioko
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3 Answers3

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You may want to use one of the wrappers for the programs, that output everything when something goes bad and swallow stdout otherwise.

One example might be cronic, just prepend 'cronic' to 'run-parts' e.g.:

# m h dom mon dow user  command
 17 *  *   *   *  root  cd / && /etc/cronic run-parts --report /etc/cron.hourly

where /etc/cronic is a place with executable cronic script, downloaded from the website mentioned.

Cyryl Płotnicki
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  • this works great.. `apt install cronic` and then put `chronic` in front of any command in crontab.. fyi, crontab -e file is located at `/var/spool/cron/crontabs/root` vs `/etc/crontab/`.. add `MAILTO=my@email.com` to it at the top.. it has 600 perms. – alchemy Jan 13 '23 at 01:10
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You should send successful email notifications to /dev/null so they disappear.

But you want to see unsuccessful email notifications.

This means you need to first direct stdout to /dev/null and then direct /dev/stderr to stdout

try changing the redirection part of your cronjobs to

>/dev/null 2>&1

See this link

pavium
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  • Wouldn't that suppress the error emails too (because they wouldn't produce any output)? Also, I need to do this for my `cron.XXX` directories which use `run-parts`, so it's not as simple as redirecting for individual scripts. – jrdioko May 29 '11 at 01:47
  • No the idea is that `stderr` is thrown away *then* `stderr` is redirected to `stdout`. I'm not sure what `run-parts` is, but however it works redirection of `stdout` and then `stderr` seems to be the way. – pavium May 29 '11 at 02:01
  • Aha, I googled `run-parts`. That does complicate the issue, doesn't it. Maybe you should avoid `run-parts` and invoke each script separately. – pavium May 29 '11 at 02:05
  • Ah ok, I understand. `run-parts` runs all scripts in directories like `/etc/cron.daily`, so the trick is passing along the redirection to the individual scripts it is running. – jrdioko May 29 '11 at 02:06
  • I think so. I couldn't find anything about redirecting *all* output from `run-parts` (not even in the `man` page I just discovered I have. – pavium May 29 '11 at 02:14
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    Are you sure about the `>/dev/null 2>&1` bit? I tested it and that funnels everything to `/dev/null`, where if you drop the `2>&1` only stdout gets removed. – jrdioko May 29 '11 at 04:42
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  • If the script is well behaved, it will write only to STDOUT if successful, and to STDERR in case there is an error.
  • By default, cron will mail everything that the script writes into STDOUT or STDERR (Arch wiki).

So, if you want to keep error notifications, don't redirect STDERR, just STDOUT:

COMMAND > /dev/null

If you do the typical >/dev/null 2>&1, you are effectively suppressing both (bash documentation).

  1. Make stdin file descriptor a copy of /dev/null.
  2. Make stderr file descriptor a copy of stdout (that already pointed to /dev/null).
morallo
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  • Even if this does not fully answer the original question, it addresses some errors in [pavium's reply](https://superuser.com/a/290058/491366). – morallo Sep 02 '15 at 09:15