Ubuntu doesn't start, how to repair its ext4 system-partition?

Question

My netbook crashed while booting Ubuntu (I accidently removed a usb stick while booting) and now doesnt start anymore. It gives the following error and goes into an ash (BusyBox built-in) shell:

mounting /dev on /root/dev failed: No such file or directory.
mounting /sys on /root/sys failed: No such file or directory.
mounting /proc on /root/proc failed: No such file or directory.

Target filesystem doesn't have /sbin/init
No init found. Try passing init= bootarg

I booted from a live CD and tried to check my Linux partition, but it doesn't work:

ubuntu@ubuntu:/media$ sudo e2fsck /dev/sda2
e2fsck 1.41.12 (17-May-2010)
e2fsck: Device or resource busy while trying to open /dev/sda2
Filesystem mounted or opened exclusively by another program?

ubuntu@ubuntu:/media$ sudo fsck.ext4 /dev/sda2
e2fsck 1.41.12 (17-May-2010)
fsck.ext4: Device or resource busy while trying to open /dev/sda2
Filesystem mounted or opened exclusively by another program?

ubuntu@ubuntu:/media$ fuser /dev/sda2
ubuntu@ubuntu:/media$ fuser /dev/sda2 -v

When I try to check the partition with Disk Utility I get the following error:

File system is NOT clean.

Mounting the partition does not work either (it just hangs). However I can see the partition in GParted and I can succesfully mount an access my windows partition on the same harddrive (I can also boot Windows from that partition).

Is there any way to repair the partition or at least save my data?

Thanks in advance!

Answer 1

Booting using an old kernel and upgrading to 10.10 solved it for me. Now I'm checking my hard disk and doing some more backups.

Answer 2

I was a victim of "Target filesystem doesn't have /sbin/init". I tried using fsck, but it didn't work because of the following problem. 

fsck: Device or resource busy while trying to open /dev/sda1
Filesystem mounted or opened exclusively by another program?

So here is the solution:

• Boot from a live Ubuntu CD

• Remove the first inode

  sudo debugfs -w /dev/sda1
  debugfs 1.41.11 (14-Mar-2010)
  debugfs: clri <8>
  debugfs: quit
  

• Restart into Live CD again and do

  sudo fsck -yv /dev/sda1
  

It will work this time.