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How to provide information about peripherals with dmesg

You want to see how your Linux system reacts to a certain peripheral being plugged in (smartphone, monitor, USB stick etc.).
dmesg can provide that information, but one needs to separate that from previous messages.
Here's how:

  • Make sure the device in question is unplugged.
  • Open a terminal, maximise it.
  • Enter dmesg -w or --follow (wait for new messages).
  • Some systems require elevated privileges for dmesg, if so prepend sudo or become superuser first.
  • After dmesg -w spat out lots of stuff and has hopefully settled down (if it hasn't that could point to a different problem), press <Enter> until your terminal window is blank.
  • Now insert the peripheral you want information about and wait a few seconds.
  • Copy all the new output that is visible now.

This can also be insightful when removing peripherals and in many other situations.