Ubuntu – How to resolve hostnames in chroot

chroot

I try to repair an broken Ubunu 14.04 with chroot. What I did, is to boot Ubuntu from USB mounted the original system that has to be repaired and changed to this system with chroot:

sudo mount /dev/sdXY /mnt 
sudo mount -o bind /dev /mnt/dev 
sudo mount -o bind /sys /mnt/sys 
sudo mount -t proc /proc /mnt/proc 
sudo cp /proc/mounts /mnt/etc/mtab 
sudo chroot /mnt /bin/bash

That worked fine, but in chroot environment I don't have access to the internet, so apt isn't able to resolve hostnames.
What am I supposed to do?

ping www.askubuntu.com

does not work either.

Best Answer

On newer Ubuntu systems, name resolution is handled by the resolvconf service, and /etc/resolv.conf is a symbolic link to /run/resolvconf/resolv.conf. You can either add a bind mount to the /run filesystem along with your other bind mounts before executing the chroot command

sudo mount -o bind /run /mnt/run

so that the chroot system picks up the host system's DNS settings or, once you're in the chrooted system, temporarily create a static /etc/resolv.conf with nameserver(s) of your choice e.g.

echo 'nameserver 8.8.4.4' | sudo tee -a /etc/resolv.conf

Related Solutions

Ubuntu – How to chroot into persistent installation

The persistant usb drive uses a compressed read-only filesystem (squashfs) and overlays a writable filesystem layer on top that stores changed files. The writable filesystem is stored in a single file (like a zip file, but without the compression - it is actually ext3, but that is unimportant)

To put everything 'back together':

Create the locations where things will go.
Make the filesystems look like whole filesystems and not files (like they do at the moment.
Join the filesystems together.
Play around with the filesystem, like like chrooting
Clean-up

I am assuming the usb drive is mounted on

 /media/usb/

Change this to the directory that contains your persistant installation when you follow these instructions.

You need to be root, or prepend sudo to every command

1. Creating stuff

Some directories need to be created:

/media/rootfs - Location where we will put the read-only filesystem
/media/cow - The location of the writable overlay
/media/persist_usb - The location where the two filesystems will be joined

this can be done with

mkdir /media/{rootfs,cow,persist_usb}

2. Make files look like filesystems

First the compressed filesystem

mount -t squashfs -o loop,ro /media/usb/casper/filesystem.squashfs /media/rootfs

(Description: Mount the filesystem.squashfs file on /media/rootfs using squashfs)

Next the writable filesystem

mount -o loop,rw /media/usb/casper-rw /media/cow

(Description: Mount the file casper-rw' on '/media/cow using a loop device)

3. Join the filesystems together

Now we are ready to join the two directories together

mount -t aufs -o dirs=/media/cow=rw:/media/rootfs=ro unionfs /media/persist_usb

(Description: Mount the union of the two directories using aufs (see unionfs) onto /media/persist_usb with /media/cow as writable and /media/rootfs as readonly)

4. Play around

I'll leave that step up to you.

5. Cleanup

Once you have finished having fun with the installation (like chrooting) you need to get rid of the stuff that was created.

First to undo step 3:

 umount /media/persist_usb

Next to undo step 2. We can do both filesystem together:

 umount /media/{rootfs,cow}

(Description: unmount /media/rootfs and /media/cow)

Finally, to undo step 1:

 rmdir /media/{rootfs,cow,persist_usb}

The changes you have made to the filesystem have been kept and you can now unmount the USB drive (if you want to).

Ubuntu – scripting chroot, how to

Create a second script (e.g. chroot.sh) and place it in your chroot/ folder.

Now edit the command in your original script to this:

chroot chroot/ ./chroot.sh

Now the script chroot.sh will be executed inside your chroot.