DMESG(8)                FreeBSD System Manager's Manual               DMESG(8)

NAME

     dmesg - display the kernel message buffer

SYNOPSIS

     dmesg [-ac] [-M core [-N system]]

DESCRIPTION

     The dmesg utility displays the contents of the kernel message buffer.  If
     the -M option is not specified, the buffer is read from the currently
     running kernel via the sysctl(3) interface.  Otherwise, the buffer is
     read from the specified core file, using the name list from the specified
     kernel image (or from the default image).

     The options are as follows:

     -a      Show all data in the message buffer.  This includes any syslog
             records and /dev/console output.

     -c      Clear the kernel buffer after printing.

     -M      Extract values associated with the name list from the specified
             core.

     -N      If -M is also specified, extract the name list from the specified
             system instead of the default, which is the kernel image the
             system has booted from.

SYSCTL VARIABLES

     The following sysctl(8) variables control how the kernel timestamps
     entries in the message buffer: The default value is shown next to each
     variable.

     kern.msgbuf_show_timestamp: 0
             If set to 0, no timestamps are added.  If set to 1, then a
             1-second granularity timestamp will be added to most lines in the
             message buffer.  If set to 2, then a microsecond granularity
             timestamp will be added.  This may also be set as a boot
             loader(8) tunable.  The timestamps are placed at the start of
             most lines that the kernel generates.  Some multi-line messages
             will have only the first line tagged with a timestamp.

FILES

     /var/run/dmesg.boot  usually a snapshot of the buffer contents taken soon
                          after file systems are mounted at startup time

SEE ALSO

     sysctl(3), syslogd(8)

HISTORY

     The dmesg utility appeared in 3BSD.

FreeBSD 15.1-STABLE-HBSD         March 7, 2026                        DMESG(8)