Hi, I am trying to get user space tracing working for an application running in a docker container. I am running lttng session daemon in another container. I mounted the unix socket locations (either /var/run/lttng for root or $HOME/.lttng for another user). By doing that I can run commands like lttng create or lttng list <session-name>, but the tracepoint events from the application don't get registered and there is no trace output.
I enabled LTTNG_UST_DEBUG an ran lttng-sessiond in verbose mode (-vvv and --verbose-consumer) and got the following error message: "*Unix socket credential pid=0. Refusing application in distinct, non-nested pid namespace.*" It appears that for some calls to the session daemon there is a getsockopt syscall made with *SO_PEERCRED* which returns 0 for pid and the call is failed with *LTTNG_UST_ERR_PEERCRED_PID* error (see get_cred call in ustctl.c). If I comment out the getsockopt call, my application tracing starts to work. >From what I found, docker cannot support getsockopt/SO_PEERCRED call to get peer pid on the unix socket which would make sense as it's in a separate namespace. I have a few questions on this: 1. What is the reason for the get_cred/getsockopt call with SO_PEERCRED? I would like to understand why it's required for some and not other calls. 2. Is there any workaround for this problem, so that I can get this to work with the container topology I am working with (app in one container and lttng daemons in another). 3. Related to 2, are there any gotchas to bypassing the getsockopt call in get_cred? Appreciate your help regarding this. Thanks, Eqbal
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