chroot from live cd

livecd2chroot.sh

#! /bin/bash

# select target root partition
if [ $1 ]
then
	root=$1
else
	# asuming the system is at the first ext partition
	root=/dev/`lsblk -f | awk '
	$2 ~ "ext" {
		print substr($1, 3);
		exit;
	}
	'`
fi

if [ $2 ]
then
	efi=$2
else
	# select first vfat partition that is not inside an iso image (that should be the EFI)
	iso=`lsblk -f | awk '
	$1 ~ "^s" && $2 ~ "iso" {
		print $1
	}
	'`
	efi=/dev/`lsblk -f | awk -v iso=$iso '
	BEGIN {
	    gsub("\n", "|", iso);
	}
	$1 !~ iso && $2 == "vfat" {
	    print substr($1, 3); # remove |- prefix
	    exit;
	}
	'`
fi

echo "selected '$root' as target root partition"
echo "selected '$efi' as target EFI partition"

read -p "Do you want to continue? [y/N] " -n 1 -r
echo
if [[ ! $REPLY =~ ^[Yy]$ ]]
then
	echo 'usage:'
	echo '	sudo ./livecd2chroot.sh [/root/partition/device/path [/efi/partition/device/path]]'
    exit 1
fi

# prepare new root fs as it is stated in the superuser community wiki
# https://superuser.com/questions/111152/whats-the-proper-way-to-prepare-chroot-to-recover-a-broken-linux-installation

# mount fs
umount $root 2>/dev/null
umount $root 2>/dev/null
mount $root /mnt
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
mount --bind /dev /mnt/dev
mount --bind /run /mnt/run
mount $efi /mnt/boot/efi

# copy network config
cp -L /etc/resolv.conf /mnt/etc/resolv.conf

# setup .bashrc
# add fancy prompt
echo 'export PS1="(chroot) $PS1"' >> /mnt/root/.bashrc
# update mtab (to operate grub)
echo 'grep -v rootfs /proc/mounts 2>/dev/null > /etc/mtab' >> /mnt/root/.bashrc

# ch[ange-]root!!
chroot /mnt /bin/bash

# restore .bashrc
sed -i '$d' /mnt/root/.bashrc
sed -i '$d' /mnt/root/.bashrc

# unmount fs
umount /mnt/boot/efi
umount /mnt/{proc,sys,dev,run}
umount /mnt