How to set up a chroot environment for RHEL, CentOS, and Fedora

Setting up a chroot environment on RHEL (Red Hat Enterprise Linux), CentOS, or Fedora allows you to work within an isolated system environment without affecting your host OS. This is useful for tasks like system recovery, testing configurations, compiling software, or experimenting with different installations. The chroot command changes the root directory for a process, creating a controlled environment that isolates operations from the rest of the system.

The process is nearly identical for RHEL, CentOS, and Fedora, as all three systems use dnf for package management. The steps involve installing a minimal system, mounting necessary filesystems like /proc, /sys, and /dev, and then entering the chroot environment for further operations.

In this guide, we will outline the steps to create a chroot environment that applies to RHEL, CentOS, and Fedora. For Fedora, ensure you use the correct release version in the dnf commands.

1. Create a directory to serve as the root for the new environment.

   $ sudo mkdir /mnt/chroot

2. Install a minimal system into the new directory.

   $ sudo dnf --installroot=/mnt/chroot --releasever=8 groupinstall "Minimal Install" # RHEL and CentOS
   $ sudo dnf --installroot=/mnt/chroot --releasever=38 groupinstall "Minimal Install" # Fedora
   Installed:  
   NetworkManager.x86_64 1.26.0-17.el8  
   chrony.x86_64 3.5-2.el8  
   systemd.x86_64 239-51.el8  
   ...

3. Mount the /proc filesystem for the chroot environment.

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

4. Mount the /sys filesystem.

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

5. Mount the /dev filesystem.

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

6. Bind /dev/pts for pseudo terminals.

   $ sudo mount --bind /dev/pts /mnt/chroot/dev/pts

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

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

8. Enter the chroot environment.

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

   Once inside, you are operating in the chroot environment for your chosen distribution. You can perform operations in isolation.

9. Install necessary software inside the chroot (optional).

   $ dnf install gcc make

10. Exit the chroot environment.

    $ exit

11. Unmount the /dev filesystem.

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

12. Unmount the /proc filesystem.

    $ sudo umount -l /mnt/chroot/proc

13. Unmount the /sys filesystem.

    $ sudo umount -l /mnt/chroot/sys