chroot is implemented by the hypervisor (umvu).
First of all download the distribution. In this example we'll use the MINI ROOT FILESYSTEM of Alpine Linux.
$$ wget http://dl-cdn.alpinelinux.org/alpine/v3.12/releases/x86_64/alpine-minirootfs-3.12.0-x86_64.tar.gz
Load the modules to virtualize uid/gid and ownership of files.
$$ vu_insmod vufs unrealuidgid
Create the directories for alpine and the virtual root home dir,
then enter the fake root environment.
$$ mkdir /tmp/alpine /tmp/root
$$ vumount -t vufs /tmp/root /root
$$ vumount -t vufs -o cow /tmp/alpine /tmp/alpine
$$ vusu -
Change dir to /tmp/alpine, set the ownership of the mount-point,
and extract the tar archive.
## cd /tmp/alpine
## chown root:root .
## tar xf /home/user/alpine-minirootfs-3.12.0-x86_64.tar.gz
This list (ls) shows that the virtualization of ownership has worked properly:
## ls -l
total 68
drwxr-xr-x 2 root root 4096 May 29 14:20 bin
drwxr-xr-x 2 root root 4096 May 29 14:20 dev
drwxr-xr-x 15 root root 4096 May 29 14:20 etc
drwxr-xr-x 2 root root 4096 May 29 14:20 home
drwxr-xr-x 7 root root 4096 May 29 14:20 lib
drwxr-xr-x 5 root root 4096 May 29 14:20 media
drwxr-xr-x 2 root root 4096 May 29 14:20 mnt
drwxr-xr-x 2 root root 4096 May 29 14:20 opt
dr-xr-xr-x 2 root root 4096 May 29 14:20 proc
drwx------ 2 root root 4096 May 29 14:20 root
drwxr-xr-x 2 root root 4096 May 29 14:20 run
drwxr-xr-x 2 root root 4096 May 29 14:20 sbin
drwxr-xr-x 2 root root 4096 May 29 14:20 srv
drwxr-xr-x 2 root root 4096 May 29 14:20 sys
drwxrwxrwt 2 root root 4096 May 29 14:20 tmp
drwxr-xr-x 7 root root 4096 May 29 14:20 usr
drwxr-xr-x 12 root root 4096 May 29 14:20 var
Now we are ready to start the chroot-ed environment.
## chroot /tmp/alpine /bin/sh
/ # cat etc/alpine-release
3.12.0
VUOS has created a virtual chroot environment.
/ # ls -l /
total 68
drwxr-xr-x 2 root root 4096 May 29 14:20 bin
drwxr-xr-x 2 root root 4096 May 29 14:20 dev
drwxr-xr-x 15 root root 4096 May 29 14:20 etc
drwxr-xr-x 2 root root 4096 May 29 14:20 home
drwxr-xr-x 7 root root 4096 May 29 14:20 lib
drwxr-xr-x 5 root root 4096 May 29 14:20 media
drwxr-xr-x 2 root root 4096 May 29 14:20 mnt
drwxr-xr-x 2 root root 4096 May 29 14:20 opt
dr-xr-xr-x 2 root root 4096 May 29 14:20 proc
drwx------ 2 root root 4096 Aug 13 19:23 root
drwxr-xr-x 2 root root 4096 May 29 14:20 run
drwxr-xr-x 2 root root 4096 May 29 14:20 sbin
drwxr-xr-x 2 root root 4096 May 29 14:20 srv
drwxr-xr-x 2 root root 4096 May 29 14:20 sys
drwxrwxrwt 2 root root 4096 May 29 14:20 tmp
drwxr-xr-x 7 root root 4096 May 29 14:20 usr
drwxr-xr-x 12 root root 4096 May 29 14:20 var
/ # sh --help
BusyBox v1.31.1 () multi-call binary.
Usage: sh [-/+OPTIONS] [-/+o OPT]... [-c 'SCRIPT' [ARG0 [ARGS]] / FILE [ARGS] / -s [ARGS]]
Unix shell interpreter
/ #