> mbr is the master boot record. Its a small amount of space on an hd > reserved for boot information. Every time you choose "install grub/lilo to > MBR, you are completely rewriting, not appending to it.
Just to be a little more clear: The MBR is the "Master Boot Record". It is not a partition, and when you partition your drive however you like and use up all the space, the MBR is still there. It is 512 bytes at the very beginning of the drive that contains the partition table for the drive and some code that the computer runs as you start it. This code is responsible for loading whatever OS you have installed. If you install Windows, Windows will overwrite the OS loading code in the MBR with code that loads Windows from whatever partition you installed Windows on. This is why installations that dual-boot Windows and Linux should install Windows first and Linux second - the Linux install that places code in the MBR gives you the option of booting Windows or Linux (this Linux boot code is either part of Grub or Lilo, two popular Linux boot loaders). The /boot partition is a different beast. In the old days the code in the MBR could only jump so far into a drive to locate the Linux OS kernel and other boot files, so they had to live near the start of the drive. The easiest way to do this was to create a /boot partition, keep the kernel and other files in there (you notice /boot has your kernel and grub or lilo files), and keep that partition at the start of the drive. The rest of the data could live anywhere on the drive, so you made "/" (and whatever else) follow /boot. Nowadays, the Grub and Lilo boot loaders don't have this restriction. /boot can be anywhere on the drive, and because of that, it doesn't need to be separate from /. When you install multiple Linux distributions, each one should have its own /boot partition because each one will be loading a different kernel. So if you want to keep /boot separate from /, you need one of each for every Linux install you place on the machine. I would recommend just keeping /boot and / the same (when you format for an install, just create "/", don't create "/boot", and decide if you want to share /home or not). The complicated part comes with booting. Each Linux install should ask you if you want to place the boot loader (like Grub or Lilo) in the MBR, in the partition, or not install one at all (you may need to be in advanced mode for some of these options). The partition option is similar to the MBR - each partition also has a little reserved area of its own that can contain additional boot code - and there is one per partition, instead of one at the start of the drive. The computer doesn't automatically use the partition-specific boot code, but the MBR, if it wants, can jump to the partition boot code and let it do the booting. This is "chain loading". There are a few ways to boot multiple Linux OS's on one machine. You can either have one Linux distro install into the MBR, let the other distros do nothing, and then edit the main Linux OS's Grub or Lilo config to tell it there are Linux distributions on the other drives. This can be tricky because if you are in a Linux OS that updates the kernel you have to edit the primary OS's configuration (and if you are running Lilo, you have to re-run it to update the MBR) so the boot loader knows you have a new kernel in your secondary OS. Another method is to let every Linux distro install Grub or Lilo to the partition boot section (so they each get their own) and then let one Linux distro install to the MBR. That one still needs the configuration edited, but the edits should be simpler because you only have to tell Grub or Lilo in the MBR to chain load the other partitions and let the secondary Grub or Lilo for each distribution do the heavy lifting. I prefer this method because each OS can update its own kernel and you don't have to go off and configure the primary boot loader each time. This is also how you can boot Windows - Windows, in addition to the MBR, also writes partition-specific boot code, and Grub can just chain load that if you select Windows from the Grub menu at boot time. I know this is a lot of information, but to do the more complicated stuff like booting multiple OS's takes a little extra work :) Read this for an example of the extreme: http://www.justlinux.com/forum/showthread.php?t=143973 -Frank -- ------------------------------------------ Frank Wallingford [email protected] _______________________________________________ Mid-Hudson Valley Linux Users Group http://mhvlug.org http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug Upcoming Meetings (6pm - 8pm) MHVLS Auditorium Oct 7 - Glade - Linux GUIs made easy Nov 4 - Google Wave Dec 2 - MythTV Jan 6 - Git
