dmesg(8) - NetBSD Manual Pages

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


NAME

     dmesg -- display the system message buffer


SYNOPSIS

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


DESCRIPTION

     dmesg displays the contents of the system message buffer.

     The options are as follows:

     -d      Show the timestamp deltas.  Used together with -t only the deltas
             are shown.

     -M      Extract values associated with the name list from the specified
             core instead of the default ``/dev/mem''.

     -N      Extract the name list from the specified system instead of the
             default ``/netbsd''.

     -T      Format uptime timestamps in a human readable form (using
             ctime(3)) using output suitable for the local locale as set in
             the environment.  Repeating this option prints the uptime in ISO
             8601 duration form, giving the duration since boot, in hours,
             minutes, and seconds (to millisecond resolution).  A third occur-
             rence causes the duration to always be represented to millisecond
             precision, even where that means trailing zeroes appear.

     -t      Quiet printing, don't print timestamps.

     The system message buffer is a circular buffer of a fixed size.  If the
     buffer has been filled, the first line of the dmesg output may not be
     complete.  The size of the message buffer is configurable at compile-time
     on most systems with the MSGBUFSIZE kernel option.  Look for MSGBUFSIZE
     in options(4) for details.


FILES

     /var/run/dmesg.boot  copy of dmesg at the time of last boot.


SEE ALSO

     options(4), syslogd(8)


HISTORY

     The dmesg command appeared in 3.0BSD.


BUGS

     The -T option will report nonsense when displaying lines from the message
     buffer that were not added by the current running kernel.

     When -TT is used, the duration is always given with maximum units of
     hours, even when the number of hours is in the hundreds, thousands, or
     more.  This is because converting hours to days, over periods when ``time
     skips'' occur, such as summer time beginning or ending, is not trivial.
     A duration of 26 hours might be 1D3H or 1D1H at such events, rather than
     the usual 1D2H, and when a time zone alters its offset, even more complex
     calculations are needed.  None of those calculations are done (even to
     account for sub-hour time zone shifts), the duration indicated is always
     calculated by simple division of seconds by 60 to produce minutes, and
     again to produce hours.  Most of the time [!] this is correct.

NetBSD 9.0                     October 30, 2018                     NetBSD 9.0