Saving%20Your%20Ass(ets)%20with%20chroot

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Saving Your Ass(ets) with chroot

• Alan Bailward ltalan_at_ufies.orggt
• April 15, 2004
• For the Fraser Valley Linux Users Group

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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

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Getting in Trouble

• Easy to have Linux problems
• Errors on install
• Broken kernel
• Broken lilo
• Normally youre out of luck, to a degree, or need
  to deal with accessing things from a BootCD

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Getting Out of Trouble

• The old way

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The Old way

• Get to your system
• Floppy
• BootCD
• Fix it
• Mess with lilo/lilo.conf
• Compile kernel, hope it works

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Getting Out of Trouble

• The New Way

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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

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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

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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)

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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

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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

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Live Demo
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Questions?