Have 3 linux distros on 3 hard drives. lost one distro from boot loader. how do I restore missing distro to boot loader? drive was not written to when one distro (drive) was updated.
Example drives a, b, and c each had listing on boot loader, now after upgrade to distro on drive b order on boot loader is drive b then a and none for c.

Which bootloader are you using? Lilo? Grub? Grub 2?

What distributions?

Which one has control of the MBR?

Are the others, written to the partition boot record?

Which bootloader are you using? Lilo? Grub? Grub 2?

Grub 2

Distributions are Ubuntu 10.04, Lubuntu 10.10 and Ubuntu 11,04
on sdc1, sdd1 and sdb1 with sda1 1000 GB Data drive

Update was to Ubuntu 11.04

Ubuntu 10.10 and 11.04 are now on boot loader
drive with 10.04 can be accessed when when either is booted

MBR appears to be on sdc1

Just boot whatever distro has control of booting the computer and run:
And hopefully all your distros will be added to your grub2 menu.
From the info you gave in your last post, I assume that Ubuntu 10.04 on sdc1 is controlling the booting of your computer. Is that correct?

Also, as AndrewThomas asked, when you installed the other *buntus did you install their grub2 to the MBR? And if so, the MBR of which hard drive? Or did you install their grub2 to their respective partitions?
If you chose to install all 3 *buntus grub2 to the MBR of the first hard drive (i.e., the one listed as first boot device in the computer's BIOS) then each time there is a kernel update for each *buntu, that *buntu's grub2 will then take over booting the computer.

Work well thanks