Sorry but that argument is illogical. The only retention period that would ensure that you always have the boot time kernel messages is 'infinity' and that's not a reasonable option for obvious reasons (c.f. LP #1618188).
** Changed in: systemd (Ubuntu) Status: Won't Fix => New -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1450588 Title: /var/log/dmesg No Longer Being Updated Status in systemd package in Ubuntu: New Bug description: After upgrading to Ubuntu 15.04 Vivid, /var/log/dmesg is no longer updated after boot. It appears that this was previously done via /etc/init/dmesg.conf To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1450588/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp