dmesg dmesg is a command used to print messages from the kernel log. It is frequently used to debug attached devices as the kernel attempts to initialize them, and to debug startup issues. dmesg log is stored in /var/log/dmesg A scenario where the output of the command may be essential could be when attaching a secondary storage device but not seeing it initialized in /dev. You could use the dmesg command to look for whether or not the kernel recognized the new hardware.