DMESG linux command manual

DMESG(8)                                                           DMESG(8)

       dmesg - print or control the kernel ring buffer

       dmesg [ -c ] [ -n level ] [ -s bufsize ]

       dmesg is used to examine or control the kernel ring buffer.

       The  program  helps users to print out their bootup messages.  Instead
       of copying the messages by hand, the user need only:
              dmesg > boot.messages
       and mail the boot.messages file to whoever can debug their problem.

       -c     Clear the ring buffer contents after printing.

              Use a buffer of size bufsize to query the kernel  ring  buffer.
              This  is  16392  by default.  (The default kernel syslog buffer
              size  was  4096  at  first,  8192  since  1.3.54,  16384  since
              2.1.113.)   If you have set the kernel buffer to be larger than
              the default then this option can be used  to  view  the  entire

              Set  the level at which logging of messages is done to the con-
              sole.  For example, -n 1 prevents all  messages,  expect  panic
              messages,  from  appearing  on the console.  All levels of mes-
              sages are still written to /proc/kmsg, so syslogd(8) can  still
              be  used to control exactly where kernel messages appear.  When
              the -n option is used, dmesg will not print or clear the kernel
              ring buffer.

              When both options are used, only the last option on the command
              line will have an effect.


       Theodore Ts'o (