LTTng » LTTng-tools

If a session is created with just the no-output option, the snapshot commands are possible, but they fail while giving the appearance of success:

$ sudo -H lttng create nooutmm --no-output
Session nooutmm created.
$ sudo -H lttng enable-channel channel0 --discard --output mmap -k
Kernel channel channel0 enmabled for session nooutmm
$ sudo -H lttng enable-event -k -a -c channel0
All kernel events are enabled in channel channel0
$ sudo -H lttng start
Tracing started for session nooutmm
$ sudo -H lttng snapshot record
Snapshot recorded successfully for session nooutmm
$ sudo -H lttng stop
Waiting for data availability
Tracing stopped for session nooutmm
$ sudo -H lttng destroy -a
Session nooutmm destroyed

Despite lttng reporting 'Snapshot recorded successfully for session nooutmm', no such capture occurs.

The lttng snapshot record command also fails if the kernel events are using the splice output mode (it is the default, after all), and again claims everything went okay. The log is essentially identical to that given above.