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thepocketwade
Asked: 2009-12-03 17:34:07 +0800 CST

Is there a reason to use /dev/lognull instead of /dev/null when logging with syslog-ng?

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At my office I recently wondered aloud to all, "Why shouldn't these logs be redirected to /dev/null instead of /dev/lognull?" I was told that there is (or was) a reason, but no one could remember it. I was told that the reasons is in the syslog-ng documentation somewhere, but so far I haven't been able to find it. Does anybody know the reason?

logging

3 Answers

  1. Best Answer

    I was just emailed this from my boss:

    Well, we named it lognull, but that was just our choice. I found the reason again. Syslog-ng wants to change the permissions on the file it uses for logging, including /dev/null. Lots of other things in the system (incl. things not running as root) depend on /dev/null being readable and writable. That's why you're supposed to use a separate device file:

    odin ~ # ls -ld /dev/null crw------- 1 root root 1, 3 Sep 30 15:48 /dev/null

    Maybe the easiest thing would be for the init script for syslog-ng to create something like /dev/lognull so it's always available for the system. I think the problem is that it goes away after a reboot because of the dynamic nature of devices now. That wasn't the case when we ran all this on older versions of Linux or on Solaris. Does this make sense?

    And I also found this thread on the syslog-ng list about the issue. So far I've followed the advice about an empty destination.

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  2. I have never heard of /dev/lognull.

    What does this return?

    ls -l /dev/null /dev/lognull

    I suppose it's possible syslog-ng is creating that device node, but man, seems very strange.

    I have to admit I'd find it pretty entertaining if /dev/lognull were a large regular file. :)

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  3. Simply define a log statement with a source but no destination: https://www.syslog-ng.com/technical-documents/doc/syslog-ng-open-source-edition/3.21/administration-guide/55#TOPIC-1180579

    To skip the processing of a message without sending it to a destination, create a log statement with the appropriate filters, but do not include any destination in the statement, and use the final flag.

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