Code review comment for ~dashmage/charm-logrotated:bug/2017798-update-cron-daily-location

I am curious

1. who is the runner when this library being called. (Ubuntu? Juju?) why they have root permission.
2. what's the different between f.flush and f.seek.
3. The logic looks like a magic if we want to copy the temp file. Is there better way to avoid the magic flush() or seek() function? I prefer not to use some implictly ability of flush() or seek() here. I prefer to make it just like a human do here.

#1 create temp file
#2 write data and close
#3 copy file
#4 delete temp file