Re: dmesg content lifetime

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.


-- 
Tomoaki AOKI    <junchoon@dec.sakura.ne.jp>