Steve Litt <slitt@???> writes:
> Kevin Chadwick via Dng said on Fri, 3 Apr 2026 10:23:31 +0100
>
>>-------- Original Message --------
>>
>>> which uses assert for invarant checks in the context of the init
>>> process. Should these asserts ever trigger, they'll stop the program
>>> via abort which will cause a kernel panic because init is special
>>> can just exit in case of a runtime error. But why would people
>>> programming in the context of init take that into account?
>>
>>Ada SPARK would be a great choice of language for pid 1 actually. As
>>you could I guess quite easily prove it to Silver level and be sure it
>>could never crash (AORE; absence of runtime errors).
>
> OK, let's do it. Let's start with a PID1 that does nothing but run a
> single shellscript and receive incoming signals. The 16 line C program
> for a PID1 that runs a shellscript shellscript and nothing else can be
> seen toward the bottom of http://ewontfix.com/14/ . The Suckless Tools
> version, which is more like 83 lines plus some .h code and responds to
> incoming signals, can be quickly and simply downloaded with:
>
> git clone git://git.suckless.org/sinit
>
> Serious business, tell me how to write the 16 line
> only-runs-shellscript version in Ada Spark.

If you want a truly minimal init, this here should do:

----
int main(void)
{
    extern int wait(int *);
    while (1) wait(0);
    return 0;
}
----

that's the part which keeps running. It can be combined with a
shell-script which could look like this:

----
#!/bin/sh
launch /etc/startup
exec reaper
----

to start the script /etc/startup as background process and then execute
the waiting program (named reaper for the sake of this example).

NB: I didn't test if running a shell script with a she-bang line as init
actually works. In theory, it should, though.