Why bind to LiveCD /proc before building initramfs ? Post: 303001550

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Top Forums UNIX for Beginners Questions & Answers Why bind to LiveCD /proc before building initramfs ? Post 303001550 by sreyan32 on Monday 7th of August 2017 07:34:11 AM

08-07-2017

Registered User

Why bind to LiveCD /proc before building initramfs ?

Imagine I have an unbootable system where I need to update the kernel image using

Code:

update-initramfs

.

I have seen numerous examples online which show the following

Code:

$ mount -t proc none /mnt/ubuntu/proc
$ mount -o bind /dev /mnt/ubuntu/dev
$ mount -o bind /sys /mnt/ubuntu/sys

After that we chroot into the broken OS and then execute the command to update the initramfs.

My questions are as follows-:

Are we binding the /proc and /dev of the Live CD to the broken system ? Or are we binding the /proc and /dev of the broken system to the live cd ?
If building the initramfs is dependent on the information of the OS for which the initramfs is built then won't it contain erroneous information if we build for the Live CD ? That is use the /proc and /dev of the LiveCD ?

Last edited by rbatte1; 08-07-2017 at 09:47 AM.. Reason: Tidied up numbered list

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dracut-shutdown.service

DRACUT-SHUTDOWN.S(8)						      dracut						      DRACUT-SHUTDOWN.S(8)

NAME

       dracut-shutdown.service - unpack the initramfs to /run/initramfs

SYNOPSIS

       dracut-shutdown.service

DESCRIPTION

       This service unpacks the initramfs image to /run/initramfs. systemd pivots into /run/initramfs at shutdown, so the root filesytem can be
       safely unmounted.

       The following steps are executed during a shutdown:

       o   systemd switches to the shutdown.target

       o   systemd starts /lib/systemd/system/shutdown.target.wants/dracut-shutdown.service

       o   dracut-shutdown.service executes /usr/lib/dracut/dracut-initramfs-restore which unpacks the initramfs to /run/initramfs

       o   systemd finishes shutdown.target

       o   systemd kills all processes

       o   systemd tries to unmount everything and mounts the remaining read-only

       o   systemd checks, if there is a /run/initramfs/shutdown executable

       o   if yes, it does a pivot_root to /run/initramfs and executes ./shutdown. The old root is then mounted on /oldroot.
	   /usr/lib/dracut/modules.d/99shutdown/shutdown.sh is the shutdown executable.

       o   shutdown will try to umount every /oldroot mount and calls the various shutdown hooks from the dracut modules

       This ensures, that all devices are disassembled and unmounted cleanly.

       To debug the shutdown process, you can get a shell in the shutdown procedure by injecting "rd.break=pre-shutdown rd.shell" or
       "rd.break=shutdown rd.shell".

	   # mkdir -p /run/initramfs/etc/cmdline.d
	   # echo "rd.break=pre-shutdown rd.shell" > /run/initramfs/etc/cmdline.d/debug.conf
	   # touch /run/initramfs/.need_shutdown

AUTHORS

       Harald Hoyer

SEE ALSO

       dracut(8)

dracut								    09/12/2013						      DRACUT-SHUTDOWN.S(8)