Re: dmesg content lifetime

On Wed, 23 Nov 2022 01:16:55 +0900
Tomoaki AOKI <junchoon@dec.sakura.ne.jp> wrote:

> On Tue, 22 Nov 2022 09:47:10 -0600 (CST)
> Dan Mack <mack@macktronics.com> wrote:
>
> > On Tue, 22 Nov 2022, Alexander Kabaev wrote:
> >
> > > On Tue, 22 Nov 2022 09:12:28 -0600 (CST)
> > > Dan Mack <mack@macktronics.com> wrote:
> > >
> > >> It seems like dmesg content ages out over time.   Is there a way to
> > >> leave the contents based on a fixed memory size instead?
> > >>
> > >> Dan
> > >>
> > > I think this is how it works: the kernel message bugger is of fixed
> > > size and kernel and syslog sequences (dmesg -a) share it. The other
> > > syslog users eventually puts enough content in there to displace all of
> > > kernel messages. If the kernel stays quiet, 'dmesg' then returns
> > > nothing, as by default it filters syslog entries that do not KERN
> > > facility out, see sbin/dmesg/dmesg.c.
> > >
> > > --
> > > Alexander Kabaev
> > >
> >
> > Thank you Alexander, I did not know this.  I'll USL (use-the-source-luke)
> > :-)
> >
> > Dan
>
> Increase kern.msgbufsize tunable on /boot/loader.conf if you want dmesg
> to live longer. For example, recommended value by iwlwifi team is
> 1146880. Much larger than default.
>
> Note that this is actually a tunable and can be set only on boot time.
>

Or look at /var/run/dmesg.boot.  It doesn't get overwritten.

--
Gary Jennejohn