init: execute /etc/rc.final after all user processes have terminated

[kevans]

Summary

This can be useful for, e.g., unmounting filesystems that were needed
for shutdown.

Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
X-NetApp-PR: #63

[gbe]

LGTM for the man page part.

[kib]

sbin/init/init.c

2061

I suggest to also check that +x bit it enabled

2077

s/ 0/NULL/ ? And perhaps without the cast?

2080

may be, say which file you execed so user understand why execl failed.

2085

Again, NULL instead of (int *)0?

[kevans]

Address feedback from kib

[kevans]

sbin/init/init.c

2061

Tossed in a warning() if it exists as non-executable