Sachin Patil

Sachin

Free software developer & Emacser

Working with chroot environment

This post covers what is chroot and why to use it? It also provides steps to create chroot environment.

As its man page says, “it is used to run commands or an interactive shell with special root directory”. It provides an environment to test new packages in a secured way without touching an actual system. It can be called as a virtual system with isolated root(/)

Why chroot environment ?

Suppose I have a new package to test and compile the package with many dependencies. Also I may have to compile each and every dependent package till my requirement for the test-package is met. This is a tedious job and the process can make my development machine highly unstable or sometime unusable, this is certainly not I want. The best way I can deal with this is to create a virtual machine, I can use Qemu or Virtual Box for that or I can just make a chroot environment in a separate directory and start compiling the package. chroot environments are also used to host web-servers, so if at all the web-server is compromised, not all the services are hampered and the system is still safe.

Another advantage of having a chroot environment is that the file-system is totally isolated from the physical host. chroot has a separate file-system inside the file-system, the difference is, it uses a newly created root(/) as it’s root directory.

Creating a chroot environment

In order to create a chroot environment, we need to create a file-system. The file hierarchy within the directory is same as any other Linux file-system such as /root, /usr, /etc, /bin, /opt etc. We can make a Debian chroot environment using debootstrap or rootstock, both are available for Ubuntu systems. In this post I will use debootstrap to create a chroot environment.

Install debootstrap using,

sudo apt-get install debootstrap

We can specify a system architecture, a suite(release name) and a mirror to download from in the debootstrap parameter.

The syntax is as follows,

debootstrap --arch <ARCHITECTURE> <SUITE> <YOUR-ROOT-DIRECTORY> <MIRROR>

for example, if I want arch to be i686 for Ubuntu 12.04(precise) and my root directory is precise-chroot/ with mirror of the content on http://archive.ubuntu.com/ubuntu, then create directory for chroot,

mkdir precise-chroot

and create a chroot environment using debootstrap,

debootstrap --arch i686 precise precise-chroot http://archive.ubuntu.com/ubuntu

this will create a chroot environment for Ubuntu 12.04, from the mirror.

chroot’ing

Once all the file are downloaded, we can chroot into precise-chroot/ directory using,

sudo chroot precise-chroot /bin/bash

where precise-chroot as the root directory, and the shell as /bin/bash. You will be landed on the root prompt. Now you can setup the package manager and update it. This will work same as any other Linux environment.

References

  • Visit the manual page - man chroot
  • Guide to rootstock
  • Why FreeBSD prefers jail instead of `chroot`?