weldr / lorax / 1095

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Pull #571

travis-ci

lorax: Move default tmp dir to /var/tmp/lorax

If systemd's tmpfiles.d timer is executed while lorax is running it will
remove any files and directories older than 30 days. This is what has
been causing the occasional error where /proc/ would seem to vanish
during the install.

Upstream has proposed this solution, https://github.com/systemd/systemd/pull/11482
but until that is released we need a work-around to protect the lorax
files.

This commit does several things:

* Move the default tmpdir from /var/tmp/ to /var/tmp/lorax/
* Add a lorax.conf tmpfiles.d file that prevents systemd-tmpfiles from
  removing anything under /var/tmp/lorax/
* Add an exit handler to lorax so that temporary directories are removed on
  exit or on a python traceback.
* Use flock to lock access to the tempdir while lorax is running.
* Remove any unlocked tempdirs named /var/tmp/lorax/lorax.* at startup

Note that the exit handler will not remove the tempdir if lorax is
killed with a signal -- those are being caught by dnf and prevent the
exit handler from running.

systemd-tmpfiles cannot clean up the tempdirs at boot time because they
contain files labeled as shadow_t, so we have to remove those when lorax
runs. It uses the flock to prevent removing any directories created by
parallel instances of lorax and only removes ones that are unlocked.
Worst case they will be around until the first run of lorax after a
reboot.

If you want to keep the working directory around for debugging purposes
use --workdir /var/tmp/lorax/my-workdir and it won't be removed by
lorax.

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