[ceph-users] How to debug problem in MDS ?

Florent B florent at coppint.com
Thu Oct 18 00:35:32 PDT 2018


I'm not familiar with gdb, what do I need to do ? Install "-gdb" version
of ceph-mds package ? Then ?
Thank you

On 18/10/2018 03:40, Yan, Zheng wrote:
> On Thu, Oct 18, 2018 at 3:59 AM Florent B <florent at coppint.com> wrote:
>> Hi,
>> I'm not running multiple active MDS (1 active & 7 standby).
>> I know about debug_mds 20, is it the only log you need to see bugs ?
>>
>> On 16/10/2018 18:32, Sergey Malinin wrote:
>>> Are you running multiple active MDS daemons?
>>> On MDS host issue "ceph-daemon mds.X config set debug_mds 20" for maximum logging verbosity.
>>>
>>>> On 16.10.2018, at 19:23, Florent B <florent at coppint.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> A few months ago I sent a message to that list about a problem with a
>>>> Ceph + Dovecot setup.
>>>>
>>>> Bug disappeared and I didn't answer to the thread.
>>>>
>>>> Now the bug has come again (Luminous up-to-date cluster + Dovecot
>>>> up-to-date + Debian Stretch up-to-date).
>>>>
>>>> I know how to reproduce it, but it seems very related to my user's
>>>> Dovecot data (few GB) and is related to file locking system (bug occurs
>>>> when I set locking method to "fcntl" or "flock" in Dovecot, but not with
>>>> "dotlock".
>>>>
>>>> It ends to a unresponsive MDS (100% CPU hang, switching to another MDS
>>>> but always staying at 100% CPU usage). I can't even use the admin socket
>>>> when MDS is hanged.
>>>>
> For issue like this, gdb is the most convenient way to debug. After
> finding where the buggy code is, set debug_mds=20 and restart mds,
> check the log to find how the bug was triggered.
>
> Regards
> Yan, Zheng
>
>
>>>> I would like to know *exactly* which information do you need to
>>>> investigate that bug ? (which commands, when, how to report large log
>>>> files...)
>>>>
>>>> Thank you.
>>>>
>>>> Florent
>>>>
>>>>
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