dpkg -l | grep linux-image
Получаем что то подобное:
rc linux-image-3.2.0-23-generic 3.2.0-23.36 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
rc linux-image-3.2.0-24-generic 3.2.0-24.39 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
rc linux-image-3.2.0-26-generic 3.2.0-26.41 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
rc linux-image-3.2.0-27-generic 3.2.0-27.43 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
ii linux-image-3.2.0-29-generic 3.2.0-29.46 Linux kernel image for version 3.2.0 on 64 bit x86 SMP
ii linux-image-server 3.2.0.29.31 Linux kernel image on Server Equipment.
Вот ядра с linux-image-3.2.0-23-generic до linux-image-3.2.0-27-generic удаляем командой:
apt-get autoremove linux-image-3.2.0-23-generic