On Wed, 14 Mar 2018 11:53:33 +0530, jitendra kumar khasdev said:

eg. when we do shutdown, which (network or storage)stack goes down first?

Hint: What order do these *have* to happen in? What happens if you shut down the network before unmounting an NFS share, or if you pixie-booted onto an iscsi-based rootfs? What happens if you spin down the disks before the network is down? (Hint 2 - how do you load /sbin/ifconfig to 'ifconfig em1 down' if the filesystem is unmounted?) For bonus points, how do you shut down all of the storage stack before everything else (since processes have a current working directory which will make the filesystem "busy")? And how do you unmount that last filesystem? :) If you're lucky enough to still be running a sysvinit-based init, boot/shutdown is controlled by the 'Knnwnatever' files in /etc/rc.d/rc5.d (usually), so perusing those will tell you most of what happens during boot and shutdown. (The quick summary- at startup, it runs all the S* scripts in order, S00whatever through S99whatever. And 'man 8 init' should have all the gory details for you. If you have systemd, you'll have to do a 'systemctl show' on each service, look at all the Name/Requires/Conflicts/Before/After/TriggeredBy tags and build an ordered graph of what gets called for what (keeping in mind that things happen in parallel, so you'll have a bazillion units that all reference network.service and a few other key checkpoints in the boot process)