Re: [mosquitto-dev] broker segfaults

[Roger Light <roger@xxxxxxxxxx>]

Hi Jacob,

I think we've got a different opinion on frequency of crashes - every
several days is appalling. Rather than running it directly in a
debugger, could you arrange to have it generate a core file when it
crashes?

To do this, you could add the lines below to /etc/init/mosquitto.conf
before the exec line, then run "sudo mosquitto stop", "sudo mosquitto
start"

limit core unlimited unlimited

The crash data could then be processed offline.

Cheers,

Roger




On Wed, Jun 22, 2016 at 1:38 PM, Jacob Lynn <abeboparebop@xxxxxxxxx> wrote:
> Unfortunately, I don't know how to reproduce it, and it happens so rarely in
> the wild (every several days for my use case) that I don't want to run in
> debug mode. But thanks for your help.
>
> On Sat, Jun 18, 2016 at 9:32 AM, Roger Light <roger@xxxxxxxxxx> wrote:
>>
>> Ok, well I'm keen to sort this out. Segfaults should never happen.
>>
>> Are you still getting the crashes? If you are, Do you think you could try
>> running the broker using valgrind or gdb? My preference would be something
>> like:
>>
>> valgrind --log-file=vglog -v --leak-check=yes /usr/sbin/mosquitto -c
>> /etc/mosquitto/mosquitto.conf
>>
>> You'd need to have debug symbols installed. On debian they are in the
>> mosquitto-dbg package, I can't remember if that applies on Ubuntu as well.
>>
>> Cheers,
>>
>> Roger
>>
>> Ok, thanks for the details. Don't think that applies to my case.
>>
>> On Jun 17, 2016 10:48 PM, "Roger Light" <roger@xxxxxxxxxx> wrote:
>>>
>>> Hi Jacob,
>>>
>>> It's possible! But pretty unlikely. This bug would manifest itself when:
>>>
>>> 1. A message with QoS>0 was published by a client that didn't have
>>> permission to publish - either through topic ACL or payload size
>>> limitations.
>>> 2. The client disconnected before the broker could complete the
>>> message flow (i.e. PUBACK/PUBREC/...)
>>> 3. The persistence file was written before the client logged in again
>>>
>>> Cheers,
>>>
>>> Roger
>>>
>>>
>>>
>>> On Tue, Jun 7, 2016 at 9:53 AM, Jacob Lynn <abeboparebop@xxxxxxxxx>
>>> wrote:
>>> > Hi all,
>>> >
>>> > I noticed the following note in the changelog for v1.4.9:
>>> >
>>> > "Fix possible rare crash when writing out persistence file and a client
>>> > has
>>> > incomplete messages inflight that it has been denied the right to
>>> > publish."
>>> >
>>> > I've been experiencing mysterious segfaults with the mosquitto broker
>>> > that
>>> > might be associated with this bug. Might this fixed bug have been
>>> > causing
>>> > segfaults?
>>> >
>>> > The broker is under a fairly consistent load of ~100-300 messages /
>>> > minute,
>>> > ~20-40 kB / minute up and down. Running v1.4.8 on Ubuntu 14.04.3.
>>> >
>>> > Best,
>>> > Jacob
>>> >
>>> >
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