[systemd-devel] Support for staged startup

[Alison Chaiken]

Marko Hoyer writes:
> > - starting up a static tree up to a final service
> > - the only job of the final service is to kick off the start of an
> > additional sub tree of units This kind of startup could be realized
> > simply by adding an additional one shot service which executes:
> > systemctl start xxx.target

Why not start the final sub-tree units the conventional way, but make
them all wait, listening on sockets?    A final service need not
contain a 'systemctl start xxx.target' command, as instead it could
simply write a message to those sockets.  Some services could receive
a signal telling them to terminate, and others telling them to
continue.

> 2.) If you wanna create some dynamics between target A and target B so that depending on the startup situation services
> are already started before A or in another round they are delayed until A is done, you probably need to disconnect them
> from the static startup tree and pull them in dynamically at the desired time.

Given that it's possible to specify the startup service in the kernel
command line with "system.unit=",  the engineer configuring the
startup sequence could specify a variety of alternate dependency
trees.    Each tree would have a different unit at its head.    The
units in one tree need not appear in another at all, or they could
appear in the second tree in a different order.

-- Alison

-- 
Alison Chaiken                           alison at she-devel.com
650-279-5600
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