Comment 6 for bug 1686138

Robie, 'apt autoremove' does not work, if there are broken packages in the system. And that usually is the case, if kernel updates have made /boot full. Even 'apt(-get) -f install' cannot deal with the space problem, as it tries to install something that does not fit. There are related bugs in other packages such as Bug #1678187, that may block removing kernels. Thus user have to take steps like described here:
https://help.ubuntu.com/community/RemoveOldKernels#Safely_Removing_Old_Kernels