dmesg: Displays Kernel Messages

The dmesg utility displays the kernel-ring buffer, where the kernel stores messages. When the system boots, the kernel fills this buffer with messages related to hardware and module initialization. Messages in the kernel-ring buffer are often useful for diagnosing system problems. When you run dmesg, it displays a lot of information. It is frequently easier to pipe the output of dmesg through less or grep to find what you are looking for. For example, if you find that your hard disks are performing poorly, you can use dmesg to check that they are running in DMA mode:

$ dmesg | grep DMA ... ide0: BM-DMA at 0xf000-0xf007, BIOS settings: hda:DMA, hdb:DMA ide1: BM-DMA at 0xf008-0xf00f, BIOS settings: hdc:DMA, hdd:DMA ...

The preceding lines tell you which mode each IDE device is operating in. If you are having problems with the Ethernet connection, search the dmesg log for eth:

$ dmesg | grep eth forcedeth.c: Reverse Engineered nForce ethernet driver. Version 0.49. eth0: forcedeth.c: subsystem: 0147b:1c00 bound to 0000:00:04.0 eth0: no IPv6 routers present

If everything is working properly, dmesg displays the hardware configuration information for each network card. If you have configured a system service incorrectly, the dmesg log quickly fills up with errors; it is a good place to start when diagnosing faults.