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

[Laura Smith]

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Wednesday, April 10, 2019 10:24 PM, Aki Tuomi <aki.tuomi at open-xchange.com> wrote:

> > On 10 April 2019 23:56 Laura Smith via dovecot < dovecot at dovecot.org> wrote:
> >
> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Wednesday, April 10, 2019 9:14 PM, Aki Tuomi < aki.tuomi at open-xchange.com> wrote:
> >
> > > > On 10 April 2019 23:13 Laura Smith via dovecot dovecot at dovecot.org wrote:
> > > > Sent with ProtonMail Secure Email.
> > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > > > On Wednesday, April 10, 2019 8:20 PM, Aki Tuomi aki.tuomi at open-xchange.com wrote:
> > >
> > > > > > 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
> > >
> > > > Only the same old cryptic message about dns-client ?
> > > > master: Fatal: execv(/usr/lib/dovecot/dns-client) failed: Permission denied
> >
> > > Something prevents executing the dns-client binary.
> >
> > > > master: Error: service(dns_client): command startup failed, throttling for 16 secs
> > > > dns_client: Fatal: master: service(dns_client): child 14293 returned error 84 (exec() failed)
> >
> > > Aki
> >
> > Yes but is it being called by doveadm directly or by some other dovecot program ? If I'm going to have to go down the AppArmor route, then I would prefer if you told me what was calling it instead of me having to un-necessarily spend time doing straces !
> >
> > Also, should I be able to call dns-client directly myself ? (or is there a way to do so to enable testing ?
>
> It is started by dovecot's master process when you connect to dns-client unix socket. You can try
>
> socat stdio unix-connect:/var/run/dovecot/dns-client
>
> I thought apparmor tells when something is blocked into kernel log? have you checked dmesg?
>
> Apologies for your frustration. 
> ---

Yeah nothing in dmesg.  I'm still hunting around to find some log somewhere but so far silence.

"socat stdio unix-connect:/var/run/dovecot/dns-client" runs but returns nothing. Is that expected ?

When you say "dovecot's master process", so  doveadm sync talks to the master process ?  So in terms of apparmor I would therefore be looking at /usr/sbin/dovecot ?  If that's the case, the relevant apparmor permisssions are already provided :
  /{,var/}run/dovecot/ rw,
  /{,var/}run/dovecot/** rw,