[systemd-devel] yum-updateonboot with Systemd

[Harald Hoyer]

On 20.07.2011 20:46, Lennart Poettering wrote:
> On Wed, 20.07.11 14:11, Matthew Miller (mattdm at mattdm.org) wrote:
> 
>> In general, it's useful to have an on-boot update service make sure any
>> updates are applied before any daemons which might be updated are
>> started.
> 
> If so it is possible to stick it between early boot and late
> boot. Use "After=sysinit.target mount.target" and "Before=basic.target"
> and "DefaultDependencies=no" for that.
> 
>> That is:
>>
>> On boot, a network-based update service runs as soon as the network is
>> available, but before any of the services which might receive updates are
>> started.
>>
>> User login services are one case, but in general "any service which might be
>> accessible to someone" should count. (If the service starts earlier but can
>> be restarted with the updated version before it is actually accessible, that
>> is fine.)
>>
>> Is this possible with systemd?
> 
> Well, systemd has an elaborate vocabulary which you use to express
> ordering requirements.
> 
> However, I don't think something like you suggest is feasible. In a
> modern environment network connectivity is dynamic: it comes and goes
> and comes and goes, and its's properties change. A robust system should
> hence not require a network to be around for booting: it should boot up
> just fine, and make use of the network as soon as it is available and
> stop using it if it isn't anymore. Many daemons work like this since
> quite some time, like Avahi or bind which listen to netlink changes. 
> 
> This goal is pretty much conflicting with what what you are asking for
> however: you want to unconditionally delay the boot until the network is
> up and we communicated with some service. 
> 
> So, yes, you can do that, by adding some complex ordering deps to your
> service, but in general i can only recommend avoiding this, to keep
> things fast, and robust and dynamic.
> 
> Lennart
> 

my suggestion is this:

- download the updates in the background while network is available
- upgrade the system on next reboot in an early phase