mount /dev/sda1 /mnt/gentoo/boot
mount -t proc proc /mnt/gentoo/proc
mount --rbind /sys /mnt/gentoo/sys
mount --rbind /dev /mnt/gentoo/dev
mount --make-rslave /mnt/gentoo/sys
mount --make-rslave /mnt/gentoo/dev
chroot /mnt/gentoo /bin/bash