Why bind to LiveCD /proc before building initramfs ? Post: 303001642

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Top Forums UNIX for Beginners Questions & Answers Why bind to LiveCD /proc before building initramfs ? Post 303001642 by Corona688 on Tuesday 8th of August 2017 11:29:22 AM

08-08-2017

Registered User

Quote:

Originally Posted by sreyan32

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-:
[LIST=1][*]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 ?

Neither. /dev and especially /proc are virtual filesystems, which don't show files but rather imaginary kernel things.

So they're neither livecd, nor your broken system, but something belonging to whatever kernel you're running.

These kernel / device interfaces are pretty hard for a system to do without.

Quote:

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 ?

It doesn't so much archive them as use them.

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update-initramfs

UPDATE-INITRAMFS(8)					      update-initramfs manual					       UPDATE-INITRAMFS(8)

NAME

       update-initramfs - generate an initramfs image

SYNOPSIS

       update-initramfs -c|-d|-u [-k version] [-t] [-v] [-b] [-h]

DESCRIPTION

       The  update-initramfs  script manages your initramfs images on your local box.  It keeps track of the existing initramfs archives in /boot.
       There are three modes of operation create, update or delete.  You must at least specify one of those modes.

       The initramfs is a gzipped cpio archive.  At boot time, the kernel unpacks that archive into RAM disk, mounts and uses it as  initial  root
       file system. All finding of the root device happens in this early userspace.

OPTIONS

	-k  version
	      Set  the	specific  kernel  version for whom the initramfs will be generated.  For example the output of uname -r for your currently
	      running kernel.  This argument is optional for update. The default is the latest kernel version.

	      The use of "all" for the version string specifies update-initramfs to execute the chosen action for all kernel  versions,  that  are
	      already known to update-initramfs.

	-c    This mode creates a new initramfs.

	-u    This mode updates an existing initramfs.

	-d    This mode removes an existing initramfs.

	-t    Allows one to take over an custom initramfs with a newer one.

	-v    This option increases the amount of information you are given during the chosen action.

	-b    Set an different bootdir for the image creation.

	-h    Print a short help page describing the available options in update-initramfs.

EXAMPLES

       Update the initramfs of the newest kernel:

       update-initramfs -u

       Create the initramfs for a specific kernel:

       update-initramfs -c -k 2.6.18-1-686

FILES

       /etc/initramfs-tools/update-initramfs.conf

AUTHOR

       The initramfs-tools are written by Maximilian Attems <maks@debian.org>, Jeff Bailey <jbailey@raspberryginger.com> and numerous others.

SEE ALSO

	initramfs.conf(5), initramfs-tools(8), mkinitramfs(8).

Linux								    2008/12/19						       UPDATE-INITRAMFS(8)