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Linux - Chroot into existing Installation

If a system does not boot anymore, it's usually easiest to boot from a live-media and chroot into the installation to troubleshoot the issue at hand. I'll be using the archlinux installation iso to chroot into a debian install to fix a kernel update that's gone sideways.

Once in the arch installation, make sure that the disks are all detected:
 root@archiso ~ # lsblk  
 NAME          MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS  
 loop0          7:0  0 853.9M 1 loop /run/archiso/airootfs  
 sr0           11:0  1  1.2G 0 rom /run/archiso/bootmnt  
 vda          254:0  0  32G 0 disk  
 ├─vda1         254:1  0  976M 0 part  
 └─vda2         254:2  0  31G 0 part  
  ├─vg_base-lv_root  253:0  0  3.8G 0 lvm  
  ├─vg_base-lv_usr   253:1  0  5.7G 0 lvm  
  ├─vg_base-lv_var   253:2  0  3.8G 0 lvm  
  ├─vg_base-lv_var_log 253:3  0  3.8G 0 lvm  
  ├─vg_base-lv_var_tmp 253:4  0  1.9G 0 lvm  
  ├─vg_base-lv_tmp   253:5  0  488M 0 lvm  
  ├─vg_base-lv_home  253:6  0  976M 0 lvm  
  └─vg_base-lv_swap  253:7  0  1.9G 0 lvm
Next, mount all the required partitions as well as /proc, /sys, /dev and /run:
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_root /mnt  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_usr /mnt/usr  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_var /mnt/var  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_var_log /mnt/var/log  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_var_tmp /mnt/var/tmp  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_tmp /mnt/tmp  
 root@archiso ~ # mount -t xfs /dev/vg_base/lv_home /mnt/home  
 root@archiso ~ # mount -t xfs /dev/vda1 /mnt/boot  
 root@archiso ~ # mount -o bind -t proc /proc /mnt/proc  
 root@archiso ~ # mount -o bind -t sysfs /sys /mnt/sys  
 root@archiso ~ # mount -o bind -t dev /dev /mnt/dev  
 root@archiso ~ # mount -o bind -t devpts /dev/pts /mnt/dev/pts  
 root@archiso ~ # mount -o bind -t run /run /mnt/run
After everything has been mounted, chroot into the installation:
 root@archiso ~ # chroot /mnt /bin/bash
The issue in my case was a missing '/boot/vmlinuz-6.1.0-37-amd64'. To check which package provides the file in question, use 'dpkg -S' on a Debian based system and reinstall it using 'apt-get reinstall':
 root@archiso:/# sudo apt-get -y reinstall $(dpkg -S /boot/vmlinuz-6.1.0-37-amd64 | cut -d ':' -f 1)
Leave the chroot environment, unmount the partitions and reboot into the Debian installation:
 root@archiso:/# exit  
 root@archiso ~ # umount -R /mnt  
 root@archiso ~ # systemctl reboot
Debian should now boot as expected.

Feel free to comment and / or suggest a topic.
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