[systemd-devel] issuing 'reboot' command does not print the familiar 'Restarting system.' message

[Lennart Poettering]

On Fri, 10.04.15 12:35, Ani Sinha (ani at arista.com) wrote:

> On Fri, Apr 10, 2015 at 10:18 AM, Ani Sinha <ani at arista.com> wrote:
> > Thanks Lennart for the clarification. Much appreciated!
> >
> > Ani
> >
> >
> > On Fri, Apr 10, 2015 at 8:58 AM, Lennart Poettering
> > <lennart at poettering.net> wrote:
> >> On Fri, 10.04.15 08:40, Ani Sinha (ani at arista.com) wrote:
> >>
> >>> On Fri, Apr 10, 2015 at 1:13 AM, Daniel Mack <daniel at zonque.org> wrote:
> >>> > On 04/10/2015 04:18 AM, Ani Sinha wrote:
> >>> >> OK I have one more question. Does every call path in the reboot
> >>> >> command use the Linux reboot() sys call? I'm not familiar with dbus
> >>> >> stuff but looking at the code seems to indicate that there might be
> >>> >> some paths where reboot() is not issued. Just wanted to run by you
> >>> >> guys since you guys know the code best.
> >>> >
> >>> > The reboot command is symlinked to systemctl, which is a multi-call
> >>> > binary. When invoked as 'reboot', 'shutdown', 'halt', 'poweroff' etc, it
> >>> > communicates with PID1 and tells it to start one of the shutdown
> >>> > targets. This way, the system will shut down and stop services in a
> >>> > clean way. Once the target is reached, the reboot() syscall is issued to
> >>> > the kernel.
> >>>
> >>> Can you please point me to the code and function call that processes
> >>> the 'reboot' target from PID 1?
> >>
> >> reboot.target pulls in systemd-reboot.service, which wraps
> >> "/usr/bin/systemctl --force reboot", which issues the Reboot() call on
> >> PID1's bus API, which causes it to execute /usr/lib/systemd-shutdown
> >> as PID 1 which then kills everything and reboots.
> 
> OK I see it now. shutdownd.c eventually issues 'shutdown -r now'. This
> gets parsed by shutdown_parse_argv(). Eventually we end up calling
> halt_main() ->halt_now() ->reboot(RB_AUTOBOOT).

Hmm?

shutdownd's only raison d'etre is to support scheduled shutdowns. It's
not used unless you actually use scheduled shutdowns. If you just use
"systemctl poweroff" or so, then it will *not* be used at all, and is
not involved at all in the shutdown logic.

And no! shutdownd will never call halt_main(), nor halt_now(), nor
reboot(RB_AUTOBOUT). If you use shutdownd, then this will result in
the equiavlent of "systemctl poweroff" and so on, just delayed a bit.

Please don't confuse shutdownd.c and shutdown.c. The former is just
there for the scheduled shutdown bits, the latter is the always used
last part of the shutdown logic.

Lennart

-- 
Lennart Poettering, Red Hat