The persistent timesyncd configuration is a single bind-mounted file
over /etc/systemd/timesyncd.conf. The NTP configuration through OS Agent
(home-assistant/os-agent#207) attempted to do atomic updates, but a
temporary file cannot be created next to it in the read-only
/etc/systemd, and replacing the file in the overlay directly changes the
inode, so the bind mount keeps pointing to the old content. Also, a
persisted copy of the whole file means changes to the shipped defaults
never reach existing installations.
Bind-mount the /etc/systemd/timesyncd.conf.d directory from the overlay
instead and keep the shipped timesyncd.conf read-only. Configuration is
layered as drop-ins, from lowest priority to higher:
* 10-ntp.conf (in /run): NTP servers from DHCP
* 20-custom.conf: timesyncd.conf imported from the CONFIG partition
* 50-os-agent.conf: NTP servers set through the OS Agent D-Bus API
On upgrade, settings from the previously persisted timesyncd.conf other
than the shipped defaults are moved to 20-custom.conf. This migration
can be removed later (with #4986). 50-os-agent.conf should be only
managed by OS Agent, so we don't need to care about user's edits.
Finally, if needed, drop-ins with higher priorities can be added for
complex customizations.
Refs home-assistant/supervisor#6278
Jan Čermák
e6d5dc0110