Working with chroot environment
This post covers what/why chroot? and also 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 with many
dependencies. Also I may have to compile each and every dependent
package till my requirement for the test-package is met. This 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 make a
chroot environment in a separate directory and start working.
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 physical machine is still safe.
An advantage of having a chroot environment is 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 its root directory.
Building a chroot environment
For chroot, 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 of Ubuntu 12.04(precise)
and my root directory is precise-chroot/ with mirror as
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 is the root directory, and the shell is
/bin/bash. You will be landed with the root prompt. Now you can
setup the package manager and update it. This will work same as any
other Linux environment.