Commands “dmesg” reads kernel messages and it is extremely usefull when you need to troubleshoot problems.

  • dmesg | grep -i usb   — shows all messages about usb devices
  • dmesg | grep -i btrfs — if you need to see how was btrfs file system mounted – options available

On Ubuntu you can look directly into file /var/log/kern.log – here you can see also timestamps for every line.