[systemd-devel] Startup single step

[Jay Burger]

Lennart/all,

Thanks for your quick responses.  I tried the systemd.confirm_spawn and got the
answer I was expecting. I agree systemd was not built to support this type
of operation and the confirm_spawn seems to work(or not) much as one would
expect. It seems to reliably fall apart the longer you wait to respond to the 
prompt.

Thanks again,

-Jay

On 07/03/2019 06:23 AM, Lennart Poettering wrote:
> On Di, 02.07.19 12:30, Jay Burger (jay.burger at us.fujitsu.com) wrote:
>
>> Hi,
>>
>> I am curious if there is a way to single step through the systemd startup
>> of services?
> So this exists, in theory in systemd.confirm_spawn= on the kernel
> cmdline. But it's not without pitfalls. In particular, some distros
> like to forcibly bind some service's stdio to the tty, which then
> interferes with the asking the user stuff. More importantly though,
> systemd implements a parallel boot, and a boot that cannot necessarily
> be linearized (for exampe: a service X that connects to a service Y
> via socket activation or bus activation necessarily means that X' and
> Y' start-up need to happen in parallel), and this makes the the
> interactive boot-up quite complicated to follow. Moreover lots of
> software tends to apply timeouts to stuff (including systemd), and if
> we interactively ask the user each time for everything these time-puts
> are hit easily. For example dbus clients generally wait for 45s at
> most for connection attempts and method calls, and since things add up
> these are hit quickly.
>
> hence, yes you can do this, but it's not particular fun, and falls
> apart quickly on complex systems, as such interactive boot-ups tend to
> behave quite differently from regular ones.
>
> Usually it's better to just turn on debug logging, and try to figure
> out things from the logs, when they happen in the same (non-)order and
> (rougly) the same timing behaviour as the regular boots.
>
>> I don't find any such feature and am curious what others would think
>> of it. We had a similar feature in a previous life, different OS,
>> and developers seemed to like it. I personally think it was a handy
>> tool to have in the arsenal, probably not a "use it all the time"
>> kind of thing.
>>
>> It could be triggered via a kernel command line option and in it's
>> simplest form, systemd would start a service and prompt the user
>> before continuing to the next. I know this would change timing and
>> dependencies may have issues but just throwing out the idea.
>>
>> This could possibly even be used to single step through the shutdown
>> of services.
> Lennart
>
> --
> Lennart Poettering, Berlin