Linux Multiboot - chroot

Preface

Goal: Updating linux in chroot environment.

Table of Content

• Preface: Table of Content

• Overview

• 1: Debian

• 2: Fedora

• 3: KaOSx

• 4: Miscellanous

• What is Next?

Overview

One advantange of multiboot is that you can update other OS, while you are still working with current OS.

Here I use openSUSE as a primary OS, while updating other OS in chroot environment

These three OS below share very similar chroot method. There are only minor differences.

• Debian

• Fedora

• KaOSx

1: Debian

Just use normal chroot method. The only issue is resolv.conf symbolic link.

chroot

Do this sequence of command, to do chroot:

% mount /media/Debian

% sudo mount --rbind  /dev /media/Debian/dev
% sudo mount --make-rslave /media/Debian/dev
% sudo mount -t proc /proc /media/Debian/proc
% sudo mount --rbind  /sys /media/Debian/sys
% sudo mount --make-rslave /media/Debian/sys
% sudo mount --rbind  /tmp /media/Debian/tmp 

% sudo chroot /media/Debian

I adapt the command above from Gentoo manual.

This will take you to Debian root.

Dio Putra suggestion

My friend, Dio Putra that has encrypted Debian partition, private message me, and gave me this suggestion.

• mount -o bind instead of mount --rbind, This rbind make this hard to be unmounted.

• umount -R instead of umount -f

• No need to bind /tmp

Rename resolv.conf

To enable internat access, we must have /etc/resolv.conf. We need to get rid of the original symlink, and replace with a new one.

/etc/resolv.conf -> /run/NetworkManager/resolv.conf

% sudo mv /media/Debian/etc/resolv.conf /media/Debian/etc/resolv.conf.symlink
% sudo cp -L /etc/resolv.conf /media/Debian/etc/

There is this other method using fstab.

• slackware chroot

/etc/resolv.conf chroot_folder/etc/resolv.conf none bind,auto 0 0

Update

# mount -a
# apt update
# apt upgrade

Restore resolv.conf

Do not forget to restore the original /etc/resolv.conf

% sudo rm /media/Debian/etc/resolv.conf
% sudo mv /media/Debian/etc/resolv.conf.symlink /media/Debian/etc/resolv.conf

Post chroot

Just exit, you will be back to original user prompt.

# exit

Unmount all

% sudo umount /media/Debian/dev
% sudo umount /media/Debian/proc
% sudo umount /media/Debian/sys
% sudo umount /media/Debian/tmp 

Sometimes the volume is busy, you need the -f argument.

umount: /media/Debian/dev: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)

Sometimes it can’t be unmount.

2: Fedora

Just use normal chroot method. The only issue is resolv.conf symbolic link.

chroot

Do this sequence of command, to do chroot:

% mount /media/Fedora

% sudo mount --rbind  /dev /media/Fedora/dev
% sudo mount --make-rslave /media/Fedora/dev
% sudo mount -t proc /proc /media/Fedora/proc
% sudo mount --rbind  /sys /media/Fedora/sys
% sudo mount --make-rslave /media/Fedora/sys
% sudo mount --rbind  /tmp /media/Fedora/tmp 

% sudo chroot /media/Fedora

This will take you to Fedora root.

# mount -a
# dnf refresh

Rename resolv.conf

But there is an issue that we have to solve with Fedora. There is no internet access, because /etc/resolv.conf does not exist. Normally we just need to copy the file, but it cannot be copied because it is a symlink to /var/run/NetworkManager/resolv.conf that does not exit.

/etc/resolv.conf -> /var/run/NetworkManager/resolv.conf

To solve this, we just need to rename

# mv /etc/resolv.conf /etc/resolv.conf.symlink

Open other terminal, and now you can copy.

% sudo cp -L /etc/resolv.conf /media/Fedora/etc/

Update

# dnf refresh
# dnf update

Restore resolv.conf

Do not forget to restore the original /etc/resolv.conf

# rm /etc/resolv.conf
rm: remove regular file '/etc/resolv.conf'? y

# mv /etc/resolv.conf.symlink /etc/resolv.conf

Post chroot

Just exit, you will be back to original user prompt.

# exit

Unmount all

% sudo umount /media/Fedora/dev
% sudo umount /media/Fedora/proc
% sudo umount /media/Fedora/sys
% sudo umount /media/Fedora/tmp 

Sometimes the volume is busy, you need the -f argument.

3: KaOSx

Just use normal chroot method. No issue at all.

chroot

Do this sequence of command, to do chroot:

% mount /media/KaOSx

% sudo mount --rbind  /dev /media/KaOSx/dev
% sudo mount --make-rslave /media/KaOSx/dev
% sudo mount -t proc /proc /media/KaOSx/proc
% sudo mount --rbind  /sys /media/KaOSx/sys
% sudo mount --make-rslave /media/KaOSx/sys
% sudo mount --rbind  /tmp /media/KaOSx/tmp 

% sudo chroot /media/KaOSx

I adapt the command above from Gentoo manual.

This will take you to KaOSx root.

Copy resolv.conf

To enable internat access, we must have /etc/resolv.conf.

% sudo cp -L /etc/resolv.conf /media/KaOSx/etc/

No need to restore anything later.

Update

# pacman -Syu

Post chroot

Just exit, you will be back to original user prompt.

# exit

Unmount all

% sudo umount /media/KaOSx/dev
% sudo umount /media/KaOSx/proc
% sudo umount /media/KaOSx/sys
% sudo umount /media/KaOSx/tmp 

Sometimes the volume is busy, you need the -f argument. Sometimes it can’t be unmount.

4: Miscellanous

Reading

• https://wiki.archlinux.org/index.php/change_root

arch-chroot

If you are in Ubuntu, you are lucky, that Ubuntu support arch-install-scripts.

Tools

• Bhaskar Chowdhury: github.com/…/change_os_root

What’s Next?

Consider continue reading [ Network: Samba ], or consider [ GhostBSD - Multiboot ].