Linux boot process -- iniramfs & root (\)

Question

I have some question related to linux boot process. Initramfs is the first stage rootfile system loaded. Init process inside iniramfs is responsible to mount actual rootfile system from harddisk to / directory.

Now my question is where is / directory created by init (init process of initramfs) to mount actual root partition. Is it in ram or hardisk ?

Also once actual root partiton is mounted then what happens to initramfs ?

If initramfs is deleted from ram then what happens to / folder created by initramfs ?

Please suggest , can some explain how does this magic works.

//Allan

Answer 1

What /sbin/init (of initramfs) does is, loads the filesystems and necessary modules. Then it tries to load the targeted real "rootfs". Then it switches from initramfs to real rootfs and "/" is on the harddisk. "/" is created when you installed the systems, done harddrive formating. Note, it's about reading the filesystem's content thus it's a prerequisite to load the required module first. If you've a ext3 partition of "/", then ext3.ko will be loaded and so.

Answer to second question - after doing the required fs module loading, it switches from initramfs's init to real rootfs's init and the usual booting process starts of and initramfs is removed from memory. This switching is done through pivot_root().

Answer to third - initramfs doesn't create any directory, it just load existing initramfs.img image into ram.

So, in short, loading iniramfs or rootfs isn't about creating any directory, it's about loading existing filesystem images. Just after boot - it uses initramfs to load must needed filesystems module, as if it can read the real filesystem. Hope it'll help!