Saving Your Ass(ets) with chroot

Alan Bailward <alan@ufies.org>April 15, 2004

For the Fraser Valley Linux Users Group

What is chroot?

Allows running of commands with an arbitrary root directory

Syntax: chroot NEWROOT [command]

Used to “jail” applications

Mostly used for security applications

i.e.: servers

Getting in Trouble

Easy to have Linux problems

Errors on install

Broken kernel

Broken lilo

Normally you’re out of luck, to a degree, or need to deal with accessing things from a BootCD

Getting Out of Trouble

The old way

The Old way

Get to your system

Floppy

BootCD

Fix it

Mess with lilo/lilo.conf

Compile kernel, hope it works

Getting Out of Trouble

The New Way

Using chroot

Lets you access your system as it was

Full access to accurate /proc and /dev

No funky pathing

Easy to jump in and out of

How To Use chroot 1

Boot with BootCD

mkdir /mnt/new

mount /dev/hda1 /mnt/new

mount /dev/hda2 /mnt/new/boot

mount /dev/hda3 /mnt/new/var

How To Use chroot 2

mount -o bind /proc /mnt/new/proc/

link the “real” /proc into your new file structure

mount -o bind /dev /mnt/new/dev/

ditto for /dev (only for devfs systems)

How To Use chroot 3

cp /etc/resolv.conf /mnt/new/etc/

need accurate network info

chroot /mnt/new /bin/bash

enter the system

env-update # gentoo only

update environment settings

How To Use chroot 4

You are now in a shell that is your old system

cd / puts you in your old / (really /mnt/new/)

Can run lilo, compile kernels, etc

To exit, type ‘exit’ to exit, then unmount disks and reboot

Live Demo

Questions?