install grub on mounted filesystem

I have booted rescue linux (init ram fs), and mounted /dev/sda1 on /mnt/sda1

/dev/sda1 is a linux partition, but /dev/sda has no mbr.

Howe can I install grub on mounted filesystem /mnt/sda1 ?

I tried:

mount /dev/sda1 sda1/
mount -t proc /proc proc/
mount -t sysfs sysfs sys
chroot .

but then, when i do grub-install /dev/sda, I get this error:

Installing for i386-pc platform.
grub-install: error: failed to get canonical path of `/dev/sda1'.