failed: read(/var/run/dovecot/dns-client)

[Aki Tuomi]

> On 10 April 2019 22:13 Laura Smith via dovecot <dovecot at dovecot.org> wrote:
> 
>  
> On Wednesday, April 10, 2019 7:57 PM, Aki Tuomi <aki.tuomi at open-xchange.com> wrote:
> 
> > > On 10 April 2019 21:26 Laura Smith via dovecot dovecot at dovecot.org wrote:
> > > ===
> > > dsync(foobar at example.com): Error: imapc(foobar.example.com:993): dns_lookup(foobar.example.com) failed: read(/var/run/dovecot/dns-client) failed: read(size=512) failed: Connection reset by peer
> >
> > This is dovecot's internal dns-client, and something goes wrong when talking to the service.
> >
> > > dsync(foobar at example.com): Error: Failed to initialize user: imapc: Login to foobar.example.com failed: Disconnected from server
> >
> > This is btw dsync service, not imap service.
> >
> > > ===
> > > Initially I thought "oh no, not another AppArmor block".
> > > But then surely the second message would not appear if the DNS lookup was not successful ?
> > > Also "dig foobar.example.com" works fine.
> > > How should I be troubleshooting this ? And if it is still likely to be AppArmor, what is calling it ? "doveadm" itself or something else ? What does "/var/run/dovecot/dns-client" do and why doesn't dovecot use standard OS calls like everyone else ?
> >
> > Because the "standard OS call" is blocking and we would prefer it to not block everything else.
> >
> > > So many questions !
> >
> > Aki
> 
> 
> Thanks for your reply, but both those message are generated from a simple :
> doveadm -v -o mail_fsync=never backup -R -u foobar at example.com imapc:
> 
> So I don't know what you mean about dsync service failing ?  Surely the DNS lookup succeeded if the 'dsync service' failed due to remote disconnect ?
> 
> I'm still none the wiser as to where to start looking for troubleshoting ?

Did you check dovecot logs? Maybe there is something useful?

Aki