According to the README file in /sys/kernel/debug/tracing/README, doing echo 1 > tracing_on should be a quick way to enable tracing. No matter how many times I execute this (as root), the value in tracing_on still remains 0. Why is that? How can I debug this further? There is no output in dmesg

tracing mini-HOWTO:

# echo 0 > tracing_on : quick way to disable tracing
# echo 1 > tracing_on : quick way to re-enable tracing

 Important files:
  trace         - The static contents of the buffer
              To clear the buffer write into this file: echo > trace
  trace_pipe        - A consuming read to see the contents of the buffer
  current_tracer    - function and latency tracers

To get this working I first had to say what to trace! To trace function calls I did this:

sudo -s # need to be root to be able to look inside /sys/kernel/debug
cd /sys/kernel/debug/tracing
echo function > current_tracer   #  trace function calls
echo SyS_inotify_add_watch > set_ftrace_filter # limit what to trace

Doing that, implicitly set the tracing flag to on, as

cat tracing_on 

Now you can also disable it

echo 0 > tracing_on

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