confused by how to generate kernel messages via /dev/kmsg [SOLVED?]

[Adam Williamson]

On Sun, 2014-05-25 at 05:12 -0400, Robert P. J. Day wrote:
> On Sun, 25 May 2014, Robert P. J. Day wrote:
> 
> >
> >   (while this is probably not technically a fedora rawhide issue,
> > since i'm trying this on rawhide, i figure this would be the best
> > place to ask about it.)
> >
> >   i really should know how to do this, but i'm confused about what
> > happens when i try to configure which "kernel" messages i generate
> > actually go to the console.
> >
> >   on my rawhide system, my current log level settings are:
> >
> > # cat /proc/sys/kernel/printk
> > 8	4	1	7
> > #
> >
> > for which my long-time understanding is that the first value
> > represents the value less than which messages of that loglevel will
> > appear on the system console -- and a value of 8 means all of them.
> >
> >   so having earlier set that first value manually with:
> >
> > # echo 8 > /proc/sys/kernel/printk
> >
> > i can now experiment by generating messages in userspace with
> > variations like:
> >
> > # echo "<0> level 0" > /dev/kmsg
> > # echo "<1> level 1" > /dev/kmsg
> > # echo "<7> level 7" > /dev/kmsg
> >
> > and so on. now if i follow the contents of dmesg in real time with:
> >
> > $ dmesg -w
> >
> > i can indeed see all of these messages adding their brief contents to
> > the dmesg buffer as i generate them.
> >
> >   *however*, only messages with log level 0 are immediately dumped to
> > all of the open xterm windows in my graphical session, which i equate
> > with the system console. any messages with log levels 1 through 7 do
> > *not* show up that way.
> 
>   never mind, i think i can see what's happening ... what gets printed
> to the console is controlled by rsyslog which is loading the "imklog"
> module, which i'm going to assume is what i would configure to change
> what log level messages go to the console, yes? so i guess i better do
> some reading up on rsyslog and, in particular, that module.
> 
>   does that sound about right?

well, in a typical modern Fedora config, journald gets its shot before
rsyslog, so it could also be interfering. check that out too.
-- 
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Twitter: AdamW_Fedora | XMPP: adamw AT happyassassin . net
http://www.happyassassin.net