[lttng-dev] one sessiond for multiuser system

[Stanislav Vovk]

Hi,

No, "Bob" did not belong to group "tracing"!

I created group "tracing", added Bob to it(as secondary group, "users" is primary) and could successfully see all events registered by program run as Bob. Thanks for that!
One problem though, when I took a snapshot with "lttng snapshot record" consumerd crashed! See below for debug output from sessiond. Seems like a bug to me, something to add to the bugtracker?

Cheers,
Stanislav

DEBUG1 [2056/2061]: Sending metadata request to sessiond, session id 0, per-pid 6 (in lttng_ustconsumer_request_metadata() at ust-consumer.c:1867)
DEBUG1 [1855/2057]: Metadata request received for session 0, key 8 (in ust_consumer_metadata_request() at ust-consumer.c:455)
DEBUG3 [1855/2057]: Buffer registry per UID find id: 0, ABI: 32, uid: 0 (in buffer_reg_uid_find() at buffer-registry.c:195)
DEBUG3 [1855/2057]: No metadata to push for metadata key 4 (in ust_app_push_metadata() at ust-app.c:441)
DEBUG1 [1855/2057]: No metadata to push (in ust_app_push_metadata() at ust-app.c:444)
DEBUG2 [1855/2057]: Consumer push metadata to consumer socket 33 (in consumer_push_metadata() at consumer.c:1175)
lttng-consumerd: ust-consumer.c:1907: lttng_ustconsumer_request_metadata: Assertion `key == channel->key' failed.
DEBUG1 [1855/1858]: Fail to receive status reply on sock 32 (in consumer_recv_status_reply() at consumer.c:58)
DEBUG1 [1855/1858]: Sending response (size: 16, retcode: Snapshot record failed) (in thread_manage_clients() at main.c:3765)
DEBUG1 [1855/2057]: Fail to receive status reply on sock 33 (in consumer_recv_status_reply() at consumer.c:58)
Error: Pushing metadata
Error: Handling metadata request
Error: Health error occurred in thread_manage_consumer
DEBUG1 [1855/2057]: consumer thread cleanup completed (in thread_manage_consumer() at main.c:1194)
DEBUG1 [1855/1858]: Clean command context structure (in clean_command_ctx() at main.c:538)
DEBUG1 [1855/1858]: Accepting client command ... (in thread_manage_clients() at main.c:3629)  


-----Original Message-----
From: jeremie.galarneau at gmail.com [mailto:jeremie.galarneau at gmail.com] On Behalf Of Jérémie Galarneau
Sent: den 9 augusti 2013 16:55
To: Stanislav Vovk
Cc: lttng-dev at lists.lttng.org
Subject: Re: [lttng-dev] one sessiond for multiuser system

On Fri, Aug 9, 2013 at 4:01 AM, Stanislav Vovk <stanislav.vovk at ericsson.com> wrote:
> Hi,
>
> Have a few questions regarding lttng configuration in a multi user system.
>
> In my system there are two users, root and Bob. I am starting sessiond at boot as root user. And instrumented programs are started as either root or Bob. I am logged in to the system and controlling lttng as root user.
>
> - When executing "lttng list -u" I see events registered by programs started as root. I don't see events from programs started as Bob. Why? Did I forget something?
>
> - Now I switch user to Bob in the shell. Executing "lttng list -u" does not give any output at all, instead a new sessiond is started. How can I have one sessiond for the whole system?

Hi Stanislav,

A non-privileged user can only interact with a root session daemon if he is part of the "tracing" group. Is it the case for "Bob" in this example?

Reproducing your scenario here with "Bob" being part of the tracing group:
- Root can list its own sessions as well as Bob's
- Bob's user space events can also be seen by root
- Bob can't see the sessions created by root.

Regards,
Jérémie

>
> Cheers,
> Stanislav
>
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--
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com