if /boot is full try removing some old kernels

Getting Started

1. You can check your current used kernel with this command:

uname -r

2. To find a list of all installed kernels on your system, run this command:

dpkg --list | grep linux-image

3. To remove all unused kernels, run now this command:

sudo aptitude purge ~ilinux-image-\[0-9\]\(\!`uname -r`\)

– If “aptitude” is not installed, then install it with this command:

sudo apt-get install aptitude

4. Update now your Grub2 boot loader with this command:

sudo update-grub2

http://www.upubuntu.com/2011/11/how-to-remove-unused-old-kernels-on.html