Bug #570765 came up earlier this week and it's bringing up the fact that when installing Ubuntu 10.04 LTS on a system with another operating system present, GRUB2 will not show the other operating system once installed for the dual/multi-boot system. It doesn't matter whether the other operating system is Microsoft Windows or another Linux installation, but the GRUB2 boot-loader doesn't offer you the option to boot that OS, just Ubuntu.
The partition(s) of the other operating system(s) are not being destroyed and the menu entries for GRUB can be re-generated using update-grub. To address this issue, Canonical engineers were just going to add to the Ubuntu 10.04 documentation a note about this and to run the aforementioned command to fix the boot-loader. They've also been planning to release a zero-day Linux kernel update for Ubuntu Lucid, which would address the issue too by automatically rebuilding the GRUB entries upon installation of the new kernel. A GRUB2 update, which would also rebuild the entries, is also in the queue for being pushed out into the Lucid repository upon its release.
Just hours ago, however, it's been decided to take the best and safest course of action -- to re-spin the ISOs. However, as it would take two days to re-spin all of the ISOs, which would then push the release into May (Ubuntu 10.05 LTS?), they have decided to just re-spin select ISOs.
Three hours ago they decided to just re-spin the Ubuntu 32-bit and 64-bit desktop CDs, but then minutes later added Ubuntu 10.04 Netbook Edition to the rebuild list and also the Ubuntu DVD if they have enough time today to re-spin and still push it out to mirrors. The maintainers of Kubuntu, Xubuntu, and the other Ubuntu derivatives are also being notified to find out if they would like to re-spin their ISOs and still can do so today.
Colin Watson also stated that "Delaying [the 10.04 release] until tomorrow is technically possible, but we'd rather get it out today since that way the folks at the release sprint are all still in London rather than traveling home as scheduled."
An Ubuntu Incident Report is available on the Ubuntu Wiki.
We had a late discovery of GRUB bootloader bug affecting dual-boot users of Ubuntu. When installing in a dual-boot environment, the other operating system will not appear at first in the GRUB menu. Installing the available updates and rebooting will fix this issue. However, it was determined the day of the release that this is not an optimal solution for new users or those not connected to the Internet.
Stay tuned for the release of Ubuntu 10.04 LTS today or tomorrow.