When I installed a new operating system on a portable external hard drive, I deliberately chose not to install grub bootloader (as it might overwrite a perfectly working MBR on the internal hard drive), as a result, /boot/grub of the new system is rather empty.

I can still boot to the new operating system using another existing bootloader. Now, I decide to install a bootloader in the MBR of the
portable hard disk, expectedly I have this:

How do I get back /boot/grub/stage1 and other files ?
If it is impossible, then I have to reinstall the OS again, what a pain!

(1) I copied /usr/share/grub/x86_64-redhat/* to /boot/grub

and
(2)
created a new /boot/grub/grub.conf

and voila, it works!!

Thanks for sharing your success!
most people don't....
I was going to comment and try to help, but my knowledge is limited
as I have never used external hd, and have never used grub.conf-is that same as menu.lst?
anyway, sometimes when installing I get the same error, so I found a work-around that sometimes works...
after above error I tried , while mounted to partition, using grub-0.97(important)
"grub-install --root-directory=/mnt/hdxx /dev/hdx"
which usually works beautifully.

What distro are you runnng?

linus72: menu.lst is soft-linked to grub.conf, so they are the same.

I am using CentOS, which is a distro that forces me to think very hard about linux. I got burned quite badly initially with the GM 965 graphic controller, but now I enjoying this distro and this graphic card, PLUS I have a portable OS ! I can now use an old HP laptop in the office. Sorry I might have bored you.

Hmmm.CentOS I know nothing about; can it do a minimal install?
Hmmmmmm.... I just downloaded net-install c5 and it works on portable-qemu too!
awesome, you use any portables?