How to set up a Gentoo chroot environment

Setting up a chroot environment in Gentoo allows you to work within a controlled Gentoo system without modifying your host operating system. This is particularly useful for tasks like compiling software, testing configurations, or repairing a Gentoo system. The chroot environment effectively simulates a full Gentoo environment, allowing operations as if you were working in the actual root system.

The process of setting up a Gentoo chroot involves downloading the necessary system components, configuring essential mounts, and entering the chroot environment to perform tasks. Unlike other distributions, Gentoo typically requires manual steps to bootstrap and configure. It is necessary to ensure all required filesystems are properly mounted, and critical system directories are available for the chroot environment to function correctly.

This guide walks you through installing a minimal Gentoo system inside a directory, preparing it with necessary mounts, and entering the chroot environment. It is designed to help you isolate operations safely, enabling repairs, testing, or new installations without affecting your main system.

1. Download the Gentoo stage3 tarball.

   $ wget https://bouncer.gentoo.org/fetch/root/all/releases/amd64/autobuilds/latest-stage3-amd64.txt
   $ wget https://bouncer.gentoo.org/fetch/root/all/releases/amd64/autobuilds/latest-stage3-amd64.tar.xz

2. Create a directory to act as the root for the new Gentoo environment.

   $ sudo mkdir /mnt/gentoo

3. Extract the stage3 tarball into the new directory.

   $ sudo tar xpvf stage3-*.tar.xz -C /mnt/gentoo
      ./bin
      ./boot
      ./dev
      ./etc
      ./home
      ...

4. Download the Gentoo Portage snapshot.

   $ wget https://bouncer.gentoo.org/fetch/root/all/releases/snapshots/current/portage-latest.tar.xz

5. Extract the Portage snapshot.

   $ sudo tar xpvf portage-latest.tar.xz -C /mnt/gentoo/usr

6. Mount /proc for the chroot environment.

   $ sudo mount -t proc /proc /mnt/gentoo/proc

7. Mount /sys for the chroot environment.

   $ sudo mount --rbind /sys /mnt/gentoo/sys

8. Mount /dev for the chroot environment.

   $ sudo mount --rbind /dev /mnt/gentoo/dev

9. Copy DNS information for internet access inside the chroot.

   $ sudo cp -L /etc/resolv.conf /mnt/gentoo/etc/

10. Enter the Gentoo chroot environment.

    $ sudo chroot /mnt/gentoo /bin/bash
    $ source /etc/profile
    $ export PS1="(chroot) $PS1"

    Once inside, you are operating in the Gentoo chroot environment. Your changes will be limited to this environment.

11. Sync the Portage tree.

    $ emerge --sync

12. Optionally, update the system.

    $ emerge --ask --verbose --update --deep --newuse @world

13. Exit the chroot environment.

    $ exit

14. Unmount /dev from the chroot.

    $ sudo umount -l /mnt/gentoo/dev{/shm,/pts,}

15. Unmount /proc and /sys from the chroot.

    $ sudo umount -l /mnt/gentoo{/proc,/sys}