LP: #1773148

LP: #1773859

On old kernels (e.g. v4.4) the file is available but appears to be
non-writable. Hide error messages and ignore failure to write out sync into the
parameters file. This does not regress https://pad.lv/1779815 since older
kernel did synchronous scan anyway. But it does resolve failure to start the
installer on old kernels.

LP: #1784454

Replace with a manual safe call to systemd-tmpfiles which will process any
updates to the tmpfiles shipped by systemd package, taking into account any
overrides shipped by other packages, sysadmin, or specified in the runtime
directories.

LP: #1748147
(cherry picked from commit 1fd144cbe31cc7a9383cc76f21f4b84c22a9dd1b)

These chages introduce all the fixes that correct handling of open fd's
realated to the DRM devices, as used by for example NVIDIA GPUs. This backport
includes some refactorings, corrections, and comment updates. This to insure
that correct history is preserved, code comments match reality, and to easy
backporting logind fixes in the future SRUs.

LP: #1777099

Retry any NXDOMAIN results with lower feature levels, instead of just those
with 'secure' in the domain name.

LP: #1766969

LP: #1768104

Configure resume offset via sysfs, to enable resume from a swapfile.

LP: #1760106

This is necessary so systemctl is functional at all times during a
dist-upgrade.

Closes: #897986
LP: #1771791

LP: #1762385

This ensures that all scans are completed, before installer reaches
partitioning stage.

LP: #1751813

If RA was iplicit, meaning not otherwise requested, and a kernel default was in
use. Do not prevent link entering configured state, whilst ndisc configuration
is pending. Implicit kernel RA, is expected to be asynchronous and
non-blocking.

LP: #1765173

LP: #1762386

LP: #1731522

LP: #1727237

LP: #1696970

LP: #1728181

LP: #1752722

On Ubuntu, systemd is the only choice, and is essential, via init ->
systemd-sysv -> systemd dependency chain, thus removing systemd is already
quite hard, and appropriate warnings are emitted by dpkg.

LP: #1758438

Only initialise NAME, after --root optional argument has been parsed, otherwise
NAME is initialized to e.g. `enable', instead of to the `unit-name`, resulting
in failures.

LP: #1752882