dhcpcd-discuss

With respect to this change,

# For ease of use, map DHCP6 names onto our DHCP4 names
 case "$reason" in
 BOUND6|RENEW6|REBIND6|REBOOT6|INFORM6)
 	new_fqdn="$new_dhcp6_fqdn"
+	old_fqdn="$old_dhcp6_fqdn"
 	;;
 Esac

Are you sure this is the right place and time to set old_fqdn?  Isn't old_fqdn needed to keep track of a previously received new_fqdn?  I would think that old_fqdn should be updated after these scripts have completed and before the next time these scripts are executed.  That would mean you need to make the change in the dhcpcd code, not in the hook script.  Maybe it would be best not to set new_fqdn to new_dhcp6_fqdn but treat each of these separately in the script.

I ran some tests with this change and I'm getting bad results.  My host name now seems to be stuck at its initial boot value and never gets updated by the hook script.