4.2BSD/usr/man/man8/dmesg.8

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.TH DMESG 8 "4 February 1983"
.UC 4
.SH NAME
dmesg \- collect system diagnostic messages to form error log
.SH SYNOPSIS
.B /etc/dmesg
[ \- ]
.SH DESCRIPTION
.I Dmesg
looks in a system buffer for recently printed diagnostic messages
and prints them on the standard output.
The messages are those printed by the system when device (hardware) errors
occur and (occasionally) when system tables overflow non-fatally.
If the
.B \-
flag is given, then
.I dmesg
computes (incrementally) the new messages since the last time it
was run and places these on the standard output.
This is typically used with
.IR cron (8)
to produce the error log
.I /usr/adm/messages
by running the command
.IP
/etc/dmesg \- >> /usr/adm/messages
.LP
every 10 minutes.
.SH FILES
.ta 2i
/usr/adm/messages	error log (conventional location)
.br
/usr/adm/msgbuf	scratch file for memory of \- option
.SH BUGS
The system error message buffer is of small finite size.  As
.I dmesg
is run only every few minutes, not all error messages
are guaranteed to be logged.  This can be construed as a blessing rather
than a curse.
.PP
Error diagnostics generated immediately before a system crash will
never get logged.