serial kernel console vs. systemd

Lennart Poettering mzerqung at
Thu May 19 18:57:02 UTC 2011

On Thu, 19.05.11 10:52, Josh Stone (jistone at wrote:

> Hi,
> I'm trying to debug some kernel crashes that I'm getting in a virtual
> machine running rawhide.  Adding "console=ttyS0,57600 console=tty0" to
> the guest kernel used to work so "virsh console my-vm" would get me all
> the kernel messages.  Now in this systemd world, I get *some* messages
> as it runs, but not everything that dmesg shows .  And I don't get
> anything when the kernel actually crashes.
> I've seen hints that systemd is reading the console=... parameters and
> remapping them through userspace.  That's not too helpful though when
> the kernel crashes such that userspace never gets a chance to echo.  Is
> there a way I can get the kernel messages directly out on serial again?

systemd does not redirect kmsg.

We actually are no longer reading console= from the kernel cmdline. We
now rely entirely on /sys/class/tty/console/active which gives us
similar information. And we use it only and exclusively to spawn a getty
on the kernel console after finishing.

Anyway, if kmsg msgs are lost for you this probably happens inside of
ply or something related, but not systemd.


Lennart Poettering - Red Hat, Inc.

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