Quoting Owen (owen@???):

> So the answer is that both /var/log/syslog and /var/log/kern.log are
> both 18GB large - see details below.

tl;dr: A hardware-based bug is making the ACPI handler stumble and
respawn, quickly, over and over and over and....

Perhaps you should consider updating your system BIOS. And, just to
make clear that I'm serious about that:

Perhaps you should consider updating your system BIOS.
Perhaps you should consider updating your system BIOS.
Perhaps you should consider updating your system BIOS.

This isn't perhaps a system using Intel Skylake CPU architecture, nei?
It's infamous for this misbehaviour, even with recent kernels like
4.9.189.

-- 
Cheers,                     "Why doesn't anyone invite copyeditors to parties,
Rick Moen                   when we're such cool people out with whom to hang?"
rick@???                        -- @laureneoneal (Lauren O'Neal)
McQ! (4x80)