Thanks for the insightful suggestions Sam.
I will definitely try some of them. I already have breakpoints
in my shutdown script and several options to pause until a key is
pressed. Currently all that my new /sbin/init script does is
touch a file and then endlessly sleep. I may need to change this
if I want to use a dynamically linked busybox. I run "telinit
u" *after* I've done a pivot_root so I don't need to worry about
overwriting the real /sbin/init even if static persistence is
enabled. All of the non-RAM file systems are safely under the
/aufs directory so /sbin is in tmpfs.
The breakpoints are very useful for debugging. They can also be
used in the field if a user's system is not shutting down
properly. AFAIK, this has never been needed. I love being able
to get to a shell, after all of the non-RAM file systems have
been unmounted, right before the final poweroff or reboot.
Having access to all the tools you need throughout the shutdown
process makes things much easier.
BTW: I use the start-time of processes to find all the processes
that need to be killed. Using pid is unreliable because it can
wrap on 32-bit systems. They can also wrap on 64-bit systems
even with /proc/kernel/pid_max set to 4194304. The start-time:
cut -d" " -f22 /proc/$pid/stat
is a long long unsigned int. So even with 1000 jiffies per
second, it won't wrap for 6 * 10^8 years. If you use pids and
they wrap then it is unlikely the shutdown will be clean.
Peace, James
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