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DMESG(8) FreeBSD System Manager's Manual DMESG(8)
NAME dmesg - display the system message buffer
SYNOPSIS dmesg [-ac] [-M core [-N system]]
DESCRIPTION The dmesg utility displays the contents of the system 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 timetamps 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 14.0-RELEASE-p11 May 7, 2022 FreeBSD 14.0-RELEASE-p11