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