A machine that backs up nothing read as missing its night after 26 hours up, and a laptop's count, last
written before it slept, read as stale on waking until the next look (novox/hq issue 489).
A hung night, a lock held for hours or a lock that cannot be taken left no
failed night behind, so it stayed healthy. The night's process now counts
how long the machine was up since its newest good night, by the monotonic
clock so a sleeping laptop is not blamed, and past 26 hours it is raised.
The retention file is written 0644 and root's instead of read through
sudo: the account reads it and still cannot change it. An unreadable file
names its cause, and the healthy answer says only what was seen.
jschoubben