Chroot is an operation that changes the apparent root directory for the current running process and their children. A program that is run in such a modified environment cannot access files and commands outside that environmental directory tree. This modified environment is called a chroot jail.
nixos-enter allows to access a NixOS installation from a NixOS rescue system.
The nixos-enter program is part of NixOS. Before it runs provides a shell, the script mounts api filesystems like /proc and setups the profile and /etc of the target system. To use it, setup
/mnt as described in the installation manual.
If a NixOS rescue system is not available, the chroot can be done manually from another Linux distribution.
Mount the file system containing the NixOS to chroot into at
/mnt, using e.g.:
mount /dev/relevantPartitionNameHere /mnt
Mount the host system's Linux run-time api file systems inside the mount, then populate
/run using the
activate script and chroot inside, starting a bash shell (adapted from here; you may copy all these lines into your terminal as one block to run them):
mount -o bind /dev /mnt/dev mount -o bind /proc /mnt/proc mount -o bind /sys /mnt/sys chroot /mnt /nix/var/nix/profiles/system/activate chroot /mnt /run/current-system/sw/bin/bash
You should now be in your NixOS system, and should be able to adjust it by e.g. editing
/etc/nixos/configuration.nix and running
nixos-rebuild switch as usual. Remember that you may have to establish Internet access the chroot for some commands.