boot: boot /boot partition fubar!

Flyboy917 · #1 26th April 2008, 04:41 AM

Call me a dumby, but I installed Ubuntu 8.04 on top of Fedora 8. The installer "said" it was creating new partitions for the instiall via resizing the drive. Cool. I "assumed" that Ubuntu would just be added to the grub boot menu. Wrong! Ubuntu now has it's own grub boot menu, and any Fedora option is not an option. However....there is still a /boot partition with fedora's version of grub and all the images still intact. I have and am running linux cdrescue on the machne at falt. I have a /dev/sda1 * boot flag and a /dev/sdb1* boot flag. I can / should only have one right?
WTF? I need to boot to Fedora.

brr872002 · #2 26th April 2008, 05:54 AM

More details needed post details of / /boot of fedora & Ubuntu
fdisk -l /dev/sda
fdisk -l /dev/sdb

Flyboy917 · #3 26th April 2008, 02:11 PM

Phew!
I was able to recovery by copying the pertinent parts of the Fedora /boot/grub.conf to Ubuntu's /boot/menu.lst. That was a close one. But hey, now I have a tri boot system!

ghost_ryder35 · #4 26th April 2008, 02:26 PM

ha, i did the same thing you did just opposite, installed fedora after ubuntu and now i have the fedora grub and I have to copy the ubuntu parts out of ubuntus's /boot/grub/menu.lst. Everytime they update the kernel you have to go in and change the statements to point to the new kernl

stoat · #5 26th April 2008, 04:00 PM

Quote:

Originally Posted by ghost_ryder35

Everytime they update the kernel you have to go in and change the statements to point to the new kernl

Hello ghost_ryder35,

Good point. But there are several ways to multi-boot Linux distros from the GRUB menu, some of which don't have that problem...

Copy the title, root, kernel, and initrd lines from one config file to another. This is what you and Flyboy917 did and are talking about. This method directly launches the kernel. A kernel update to a system booted this way requires an edit to the grub.conf because the version numbers are then different. Still, it's a popular way to do it.

Use the chainloader menu command in grub.conf. This method requires the system being booted this way to have GRUB stage1 installed in the first sector of its boot partition. The chainloader command works by loading and executing that boot sector code. The normal GRUB sequence of events starts up again at that point resulting in the GRUB menu of the selected system being displayed. That is why this method is not affected by a kernel update. This is also how GRUB boots XP.

Code:

How GRUB Boots Another Linux With the Chainloader Menu Command

                                            grub.conf                  /--> kernel
                                                |                     /
BIOS --> GRUB stage1 --> GRUB stage1.5 --> GRUB stage2 --> GRUB Menu -----> kernel
         (Master Boot     (DOS Compat      (/boot/grub)               \
            Record)          Area)                                     \--> chainloader +1
                                                                                /
                                   /<------------------------------------------/
                                  /
                                 /          grub.conf                  /--> kernel
                                /               |                     /
                           GRUB stage1 --> GRUB stage2 --> GRUB Menu -----> kernel
                          (Boot Sector)     (/boot/grub)              \
                                                                       \--> kernel

Example of a grub.conf section...

Code:

title Fedora
root (hd1,0)
chainloader +1

Use the configfile menu command in grub.conf. This method works by reloading the GRUB menu but using the information in the grub.conf of the system being booted this way. This method is also not affected by a kernel update. It also works regardless of where GRUB stage1 is installed.

Code:

How GRUB Boots Another Linux With the Configfile Menu Command

                                            grub.conf                  /--> kernel
                                                |                     /
BIOS --> GRUB stage1 --> GRUB stage1.5 --> GRUB stage2 --> GRUB Menu -----> kernel
         (Master Boot     (DOS Compat      (/boot/grub)               \
            Record)          Area)            \    \                   \--> configfile
                                               \    \                           /
                                                \    \        The other        /
                                                 \    \<----- grub.conf <-----/
                                                  \
                                                   \  
                                                    \                  /--> kernel
                                                     \     The other  /
                                                      \--> GRUB Menu -----> kernel
                                                                      \
                                                                       \--> kernel

Example of a grub.conf section...

Code:

title Fedora
configfile (hd1,0)/grub/grub.conf

Or, if there is NOT a separate boot partition...

Code:

title Fedora
configfile (hd1,0)/boot/grub/grub.conf

stoat · #6 26th April 2008, 04:16 PM

Quote:

Originally Posted by Flyboy917

I have a /dev/sda1 * boot flag and a /dev/sdb1* boot flag. I can / should only have one right?

Hello Flyboy917,

This never got answered. Answer: Every drive usually has an active partition. But forget all about active partitions when thinking about GRUB booting something. GRUB boots in stages that each know where the next stage is located. MS systems rely on active partitions for booting. It's the MS way, but GRUB never considers it.

The rare exception: It's possible to leave MS boot code in the master boot record, install Fedora (or any Linux) with GRUB stage1 in its boot sector, set that partition to be the active partition, and Fedora will then boot directly from BIOS. It's an interesting but rarely discussed dual booting method.

Code:

BIOS --> MBR with MS boot code   ---> Active partition boot code  --> Fedora boots
         which examines the           which in this example is
         partition table for          GRUB stage1 which then runs
         the active partition         stage2, etc.
         and runs its boot
         sector code.

Flyboy917 · #7 26th April 2008, 05:33 PM

stoat,
Good stuff. Thanks.
Flyboy