|This article is of interest to the following WikiProjects:|
- There must be a way of doing a tail -f on dmesg. That may be worth noting. People will probably come to this page for all sorts of info on the dmesg command and this could be very useful information. --188.8.131.52 14:38, 16 February 2007 (UTC)
http://www.kernel.org/doc/man-pages/online/pages/man8/dmesg.8.html doesn't work —Preceding unsigned comment added by 184.108.40.206 (talk) 10:49, 12 October 2008 (UTC)
Removed dmesg Output
The examples of output gave nothing to the article. It was also was beginning to sprawl; we already had Linux, FreeBSD, and some router OS. As there are an infinite possibilities of what a dmesg output can contain I see little reason in having an example in the article. Dmesg output can be best explained in the article rather than in a multitude of examples. Ismouton (talk) 04:15, 13 November 2008 (UTC)
I can't agree. Any examples at all would greatly improve this article. It seems like the two of you are so well acquainted with the dmesg output contents that you are not considering article readers who have never seen such output. If the examples were getting out of hand they should have been judiciously trimmed down. Please put some examples of dmesg output back in the article. -220.127.116.11 (talk) 13:49, 24 June 2009 (UTC)
- I agree with the previous consensus. There is very little you can say about dmesg output that is actually about dmesg. It is almost by definition OS and hardware specific. Let's consider one line of dmesg output from a system here:
clock0 at obio0 slot 0 offset 0x200000: mk48t08
- What does this tell us? At first sight it tells us about a clock. The reference to an obio bus marks it as being a particular generation of Sun machine. The clock chip is an mk48t08. Real gurus will look at this message and notice from subtle differences in the ordering and formatting of details that this is from a system running NetBSD rather than Solaris or Linux. All very interesting. What does any of that actually have to do with dmesg? Nothing at all. Remember - dmesg is a tool for viewing messages - it has nothing to do with the messages themselves, and indeed dmesg is actually a secondary user of those messages. Would you give examples of cat output with an arbitrary file? Certainly not. dmesg is a similar tool only it works with arbitrary kernel messages rather than a file as its data source. CrispMuncher (talk) 16:23, 24 June 2009 (UTC)
As the article mentions, the boot screen output typically scrolls too fast to read. As the article does not mention, if the boot process fails, there is no way to run dmesg, so the source of the problem cannot be determined.
It is nuts that there is no standard way to slow, pause, and/or single-step the boot process screen output. Presumably there is some ancient old-school way to direct the output to a serial port for capture on another computer. It would be good to at least link to such information from this article. And maybe it is worth mentioning the possibility of video recording the screen during the boot process?
Do any *nix have boot parameters to direct a copy of the boot output to floppy or USB for debugging systems that fail during boot?
Yes it is available on various Unix-like systems like FreeBSD (https://www.freebsd.org/cgi/man.cgi?query=dmesg&apropos=0&sektion=0&manpath=FreeBSD+11.0-RELEASE+and+Ports&arch=default&format=html) and OS X (https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man8/dmesg.8.html); and although it has been made obsoleted by syslogd on Solaris systems, it remains available (https://docs.oracle.com/cd/E26502_01/html/E29031/dmesg-1m.html). But if you have sources for alternatives then go ahead and add it. Cheers. Furquan-lp (talk) 15:14, 29 May 2017 (UTC)
Some issues that should be explained
dmesga command and/or a log file?
- Does it log only the current session?
- If so, does the file
dmesg.0contain the output from the previous session?
- If so, does the file
- What do the numbers at the start of each line signify? There are long sequences of lines that start with the same number before the decimal point, then that number jumps to some rather higher number. Why doesn't 1 follow after 0?
- Numbers at beginning of each line are timestamps. In recent editions of linux etc, you can use dmesg -T option to show timestamp in human-readable format. Raw format is higher resolution though, which is occasionally useful. Gwideman (talk) 01:31, 5 January 2016 (UTC)
Added some citations
This article was without any real citations before so I've added some references here and there. Feel free to check them for notability or verifiability. If anything is out of place or irrelevant, please notify me, I'll do my best to correct that error.