dmesg (for "display message") is a command on Unix-like operating systems that prints the message buffer of the kernel.
When the computer system is initially started ("booted," "boots up"), the kernel is loaded into memory, then the various parts of the kernel initialize themselves. Frequently, the kernel must "discover" the exact characteristics of the hardware it is running on, and then initialize itself appropriately. As these steps take place, diagnostic and informational messages are produced ... and they flash by, far too quickly to read. The dmesg command, therefore, enables those messages to be reviewed after the system has started.
The output of dmesg is quite long. For this reason, this output is normally reviewed using standard text-manipulation tools such as tail, or grep. The output is often captured in a permanent system logfile via a logging daemon, such as syslog .