[lxc-users] systemd's journald using 100% CPU on Debian Jessie container and Fedora 20 host
Michael H. Warfield
mhw at WittsEnd.com
Thu Oct 9 15:13:47 UTC 2014
On Thu, 2014-10-09 at 08:27 -0300, Daniel Miranda wrote:
> I spun up a Jessie container in my Fedora 20 (x86_64, LXC 1.0.5) box
> and the journald process inside the host consumes full CPU time for
> one core.
>
> I've Googled a bit and found some reports of that being connected to a
> bug that is allegedly already fixed in systemd, or related to the kmsg
> device being improperly set up, but my case doesn't seem to fit
> either: Jessie is using systemd 215 which is pretty recent,
> and /dev/kmsg points to /dev/console, which looks correct.
What? Wait... NO!
You must NOT have a link from /dev/kmsg pointing to /dev/console. In
the host it should be a real device. In a container it must NOT exist.
That is the problem. When /dev/kmsg points to /dev/console,
systemd-journald reads from /dev/kmsg and then writes to /dev/console
(which it then reads from /dev/kmsg and writes again to /dev/console ad
infinitum). You've inadvertently created a messaging loop that's
causing systemd-journald to go berserk on your CPU.
> Does anyone know what the problem might be, or if there is a
> workaround I can do in the meanwhile?
This is the first I have heard of this in a Debian container but the
answer is the same as for Fedora 19 and Fedora 20 containers...
*) Shut down the container.
*) Add "lxc.kmsg = 0" to the container config.
*) Delete ${LXC_PATH}/${container}/rootfs.dev/kmsg
*) Restart container.
If that link is in your host system /dev, you have hosed something up
seriously. That should be a device (but only in the host /dev).
> Regards,
> Daniel Miranda
>
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--
Michael H. Warfield (AI4NB) | (770) 978-7061 | mhw at WittsEnd.com
/\/\|=mhw=|\/\/ | (678) 463-0932 | http://www.wittsend.com/mhw/
NIC whois: MHW9 | An optimist believes we live in the best of all
PGP Key: 0x674627FF | possible worlds. A pessimist is sure of it!
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