18.04 timesyncd stop working after rack controller installed

[Dylan Wang]

This is an upstream bug from systemd, see details here:

https://github.com/systemd/systemd/issues/7883

But it's directly triggered by install maas -> avahi-daemon enabled -> nsswitch.conf changed.

`timedatectl status` will always return "System clock synchronized: no" on rack controller host.

systemd-timesyncd will exit immediately after start, strace /lib/systemd/systemd-timesyncd give me the following error:

```
writev(2, [{iov_base="Cannot resolve user name systemd"..., iov_len=58}, {iov_base="\n", iov_len=1}], 2Cannot resolve user name systemd-timesync: No such process
) = 59
exit_group(1) = ?
+++ exited with 1 +++
```

I'm not sure if maas can provide some workaround on this by default, right now I fix it by:

sudo useradd -r systemd-timesync

[Dan Streetman (ddstreet)]

@hyuwang the commit that fixes this appears to be:
https://github.com/systemd/systemd/pull/7884/commits/444c1915f94d7109b5fd97277b049ed17289848d

and that's already contained in systemd in Bionic (and later). Are you having this problem on Xenial?

[Dan Streetman (ddstreet)]

please reopen if this is still an issue