Resolvido com o seguinte código para o Ubuntu 16.04, conforme explicado aqui
mount /dev/sda1 /mnt
for dir in /dev /dev/pts /proc /sys /run; do
mount --bind $dir /mnt$dir
done
chroot /mnt
update-grub2
Eu decidi mover o Ubuntu 16.04 do HHD (sdb) para o SSD (sda). Começou no live-usb, copiou o / media, atualizou o UUID no fstab.
O próximo passo é fazer o GRUB funcionar no SSD, então eu tentei instalar o GRUB, enquanto no live-usb. Apesar do final "Instalação finalizada. Nenhum erro reportado." Quando eu inicializo o computador no BIOS a partir do disco SSD, ele ainda pede um disco inicializável.
O / media copiado tem grub 2.something
mint@mint ~ $ sudo grub-install --root-directory=/media/mint/SSD1 /dev/sda
grub-probe: error: failed to get canonical path of '/cow'.
Installing for i386-pc platform.
grub-install.real: warning: Sector 32 is already in use by the program 'FlexNet'; avoiding it. This software may cause boot or other problems in future. Please ask its authors not to store data in the boot track.
Installation finished. No error reported.
sudo fdisk -l
Disk /dev/sda: 128.0 GB, 128035676160 bytes
255 heads, 63 sectors/track, 15566 cylinders, total 250069680 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x73b46703
Device Boot Start End Blocks Id System
/dev/sda1 2048 233066495 116532224 83 Linux
/dev/sda2 233066496 250068991 8501248 82 Linux swap / Solaris
Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xbbc58b91
Device Boot Start End Blocks Id System
/dev/sdb1 2048 318919887 159458920 7 HPFS/NTFS/exFAT
/dev/sdb2 318920702 976771071 328925185 5 Extended
/dev/sdb5 960151552 976771071 8309760 82 Linux swap / Solaris
/dev/sdb6 318920704 960151551 320615424 83 Linux
Partition table entries are not in disk order