If local Dovecot stops working, check lo

[Jochen Bern]

On 07/12/2014 01:41 PM, Reindl Harald wrote:
> Am 12.07.2014 13:31, schrieb Steve Litt:
>> A malfunctioning lo will cause Dovecot not to connect to clients. My
>> experience with Debian Wheezy is that lo "goes down" a lot, so this is
>> one of the first things I do when odd stuff happens
> 
> uhm if you *loopback device* goes down your machine has a serious
> problem - within 15 years Linux expierience i never faced a broken
> "lo" device and i guess the same for 99.9999% of all admins

While I *am* part of those 99+%, I would like to point out that there
*also* is a lot of stuff that is perfectly normal for run-of-the-mill
network interfaces, but likely has never been tried by said 99+ with lo,
either. In particular, the following possibilities come to my mind:

1. Flaky IPv6 support (which wouldn't affect "127.0.0.1" directly, but
   might cause frequent changes of lo to add/remove/repeat ::1)
2. New interface naming schemes (I note that while eth0 starts to appear
   under all sorts of fancy names, nonempty iptables rules still
   routinely do a "-i lo -j ACCEPT" name reference in filter/INPUT)
3. Taking ntpd's 127.127.x.y pseudo-IPs for clocks a tad too literally

To sum it up - I think that you *do* want to try and nail a root cause
there.

Regards,
								J. Bern
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