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 ?
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Reason: Tidied up numbered list
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Discussion started by: Azrael
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LEARN ABOUT CENTOS
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)