When recovering from systermd-related breakage while first trying out
Debian jesse, I ended up booting with init=/bin/bash a lot.

You can rather easily bring up a fully functional system that way, at least
for long enough to fire up a browser, find the problem, and then recover.

My process for doing so was fairly simple.
- boot into bash
- remount / rw
- mount the rest of the filesystems
- start up udev (this was early in unstable or testing I think when it
wasn't merged with systemd yet)
- start up screen
- bring up network interfaces
- start up "important" system services (cron, syslog, and friends)
- fire up a display manager (not strictly required, but easy enough to do,
so why not)

I'd suggest that this is a really good way to understand what's actually
necessary to bring up the system, without writing a bit of cod, and
reproducing the steps by hand provides the level of understanding that a
sysadmin needs to have of init IMHO.



On Sun, Jun 19, 2016 at 2:30 AM Edward Bartolo <edbarx@???> wrote:

> Hi,
>
> System initialisation is NO religiously enshrined mystery that is
> highly claimed to be beyond human comprehension. I can understand the
> position help by anyone that an init is so central to an OS that it
> must be coded scrupulously. And, given time, I think, I will
> eventually come back with something that can be said to be a
> functional and stable init.
>
> My current task if of trapping system wide events like requests for
> shutdown and reboot. My init will be used to call various scripts or
> executables depending on the type of event.
>
> Edward
>
> On 18/06/2016, Rainer Weikusat <rweikusat@???> wrote:
> > Lars Noodén <lars.nooden@???> writes:
> >> On 06/17/2016 09:36 PM, KatolaZ wrote:
> >> [snip]
> >>> Unfortunately, system initialisation is really a bit more complicated
> >>> than that, whether you like it or not.
> >> [snip]
> >>
> >> Is there a concise summary somewhere of what system initialization
> >> entails? Or is it dependent on accumulated experience and not codified?
> >
> > This depends heavily on what the system is supposed to do. Eg, something
> > fairly specialized running a single application could just run the
> > application as sole process instead of init. For something more general,
> > there'll be a static initialization step which will usually include
> > creating an initial filesystem namespace by mounting some set of
> > filesystems (some virtual, eg, proc and sys, others residing on real
> > devices) and my also include configuring some set of network
> > interfaces. Afterwards, a set of programs performing various functions
> > is started, eg, web server, name server, ssh server or so-called gettys
> > enabling interactive logins without going over a network.
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> >
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