Working on chroot environments
Published on Feb 25, 2013 by Sachin.
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.