Minha pasta de inicialização estava cheia. Eu removi alguns kernels antigos. Você poderia informar quais desses itens também podem ser eliminados?
gideon@gideon:~$ uname -r
4.10.0-32-generic
gideon@gideon:~$ ls /boot
abi-4.10.0-27-generic memtest86+.bin
abi-4.10.0-28-generic memtest86+.elf
abi-4.10.0-30-generic memtest86+_multiboot.bin
abi-4.10.0-32-generic System.map-4.10.0-27-generic
config-4.10.0-27-generic System.map-4.10.0-28-generic
config-4.10.0-28-generic System.map-4.10.0-30-generic
config-4.10.0-30-generic System.map-4.10.0-32-generic
config-4.10.0-32-generic vmlinuz-4.10.0-27-generic
efi vmlinuz-4.10.0-27-generic.efi.signed
grub vmlinuz-4.10.0-28-generic
initrd.img-4.10.0-27-generic vmlinuz-4.10.0-28-generic.efi.signed
initrd.img-4.10.0-28-generic vmlinuz-4.10.0-30-generic
initrd.img-4.10.0-30-generic vmlinuz-4.10.0-30-generic.efi.signed
initrd.img-4.10.0-32-generic vmlinuz-4.10.0-32-generic
initrd.img-4.8.0-36-generic vmlinuz-4.10.0-32-generic.efi.signed
lost+found