Recover Ubuntu inode exhaustion when apt-get broken

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When inodes run out, Ubuntu can fail to install the latest kernel but can still have a dependency on it (via a pacakage like `kernel-generic`)

This leads to an error message when trying to run any `apt-get` commands about a missing dependency requiring you to run `apt-get -f install` with no args to grab the missing dep.
Doing this will fail though, as there are no inodes left...

To resolve this, you can artificially drop the number of inodes by zipping up files.
A great candidate for this is the old kernals in `/usr/src`.

1. Check the current running kernal version with `uname -r`
2. Select a couple of kernal versions in `/usr/src` which do *NOT* have the same version number as the running one, nor are the most recent.
3. Compress these kernal directories with `tar -zcf /var/tmp/<kernel-version>.tar.gz` and `tar -zcf /var/tmp/<kernel-version>-generic.tar.gz`
4. Remove the kernel folders we just backed up to free up some inodes (`rm -r <kernel-version>`)
5. Run `apt-get -f install` to fix the missing dep.
6. Run `apt-get autoremove` to now strip out more of the old kernels and resolve the issue!

If you run into problems with the `autoremove` of the backed up kernel, you can untar (`tar xf <kernel-version>.tar.gz`) and restore the files and re-run the apt command.