babeltrace2-source.text.dmesg — Babeltrace 2's Linux kernel ring buffer source component class
A Babeltrace 2 source.text.dmesg message iterator reads the lines of a Linux kernel ring buffer, as printed by the dmesg(1) tool, and emits corresponding event messages.
Linux kernel ring buffer lines (file or standard input) | | +----------------+ | | src.text.dmesg | '-->| | | out @--> Messages (single stream) +----------------+
See babeltrace2-intro(7) to learn more about the Babeltrace 2 project and its core concepts.
A source.text.dmesg message iterator names the events it creates
string. Each event contain a single payload string field named
which contains the corresponding ring buffer line.
By default, a source.text.dmesg message iterator reads the lines
of the standard input stream. You can make the message iterator read the
lines of a text file instead with the
By default, the message iterator tries to extract the timestamps of the kernel ring buffer lines and use them as the created events’s timestamps. A typical dmesg(1) line looks like this:
[87166.510937] PM: Finishing wakeup.
[87166.510937] part is the timestamp to extract. When this
information is available, the component creates a clock class which does
not have the Unix epoch as its origin.
You can make the message iterator not extract timestamps from lines with
NoteIt is possible that the output of dmesg(1) contains unsorted lines,
that is, their timestamps go back in time. You can see this with the
--show-delta option of dmesg(1): some time differences can be
This is due to a 2019 change to the kernel’s ring buffer API.
As of this version, a source.text.dmesg message iterator requires that the input kernel ring buffer lines be sorted by timestamp (when they have timestamps), failing otherwise.
Do not extract timestamps from the kernel ring buffer lines: set the created event’s payload’s
strfield to the whole line, including any timestamp prefix.
Read the kernel ring buffer lines from the file
PATHinstead of the standard input stream.
+----------------+ | src.text.dmesg | | | | out @ +----------------+
Single output port.