>>  you need to be able to convey more information to pid 1
>>  than a few signals can.
>such as ?
>what more information than the runlevel (0 or 6, maybe 1 to go
>into single user) does SysV init need to start the system shutdown ?

The time of the shutdown. The "shutdown" command isn't necessarily
instantaneous, it can register a shutdown for a given time.
  You could deal with that by creating another process, which is
equivalent to running a daemon outside pid 1 (and that's exactly
what s6-linux-init-1.0.0.0 does), but if you want to handle it all
in pid 1, you need time management in it and that can't be done
via signals only.


>the Void Linux team just made a shell script out of it that just brings
>down the runit services and runsvdir itself.

  Yeah, that's not difficult. What is difficult is implementing the
legacy features of other inits.

--
  Laurent