[systemd-devel] needed steps to get rebootless upgrade

[Koen Kooi]

Op 17 feb. 2014, om 14:50 heeft Lennart Poettering <lennart at poettering.net> het volgende geschreven:

> On Mon, 17.02.14 08:16, Vasiliy Tolstov (v.tolstov at selfip.ru) wrote:
> 
>> Hi all. I'm very interesting on creating system like cromeos that can
>> do upgrade without reboot.
> 
> ChromeOS doesn't support reboot-less upgrades. 
> 
>> In case of using systemd - what i need to do?
>> I have two disk (ramdisk) system1 and system2 that have old (system1)
>> and new (system2) filesystems.
>> How can i get upgrade system1 with system2?
>> As i understand i need to reload each running service to use new
>> system2 for it?
>> Can somebody says me more detailed steps to get this?
> 
> Such reboot-less upgrades are hardly possible. There are large parts of
> the system you cannot upgrade during runtime, such as the kernel or
> dbus-daemon and other bits. And even if you could replace all these
> things, upgrades during runtime between arbitrary versions unlikely
> would be well tested, and hence risky business...
> 
> Anyway systemd won't help you with this I fear...

If we stretch the definition of 'reboot' a bit, would it be possible to shutdown, jump back into the initramfs, do the updates and jump to the main rootfs again? It assumes you have an initramfs and all your apps will close, but the machine doesn't reboot :)

regards,

Koen