Partitioning for multiple systems

[Tim Judd]

On Sun, Apr 26, 2009 at 12:45 PM, Michael David Crawford <mdc at prgmr.com>wrote:

> I have a machine I plan to use solely for testing.  I have FreeBSD
> 8.0-CURRENT on it right now, and would like to add FreeBSD 7.2-RC2 as well
> as CentOS 5.3 Linux.
>
> Presently I have three Master Boot Record primary partitions - "slices" in
> the FreeBSD parlance, if I understand correctly:
>
> - A Linux slice to be used for CentOS' /boot
> - A BSD slice subdivided into partitions that hold 8.0-CURRENT
> - A big FAT slice (so to speak) meant to be split up for 7.2 and CentOS
>
> A PC-style Master Boot Record can hold a maximum of four primary
> partitions, or it can hold three primaries and a single extended partition
> that is subdivided into logical partitions.
>

FreeBSD's standard bootloader (not boot0) will only boot off the first
0xA5/dec.165 partition it finds.  I've never tried multibooting with boot0.

I don't recall FreeBSD supporting extended partitions... at all

The 4-entry MBR will be the problem   GPT (GEOM Partition Table) bumps that
limit up to like 127 entries.

you'd have to use an external non-native (terms of boot0 versus 'standard')
boot loader to start working.





You might utilize a 5.25" HDD enclosure as a solution to run multiple OSs on
a box.  The enclosures are pretty inexpensive and I have enjoyed working
them that way.



> The geometries of the logical partitions aren't given in the MBR, but exist
> as a linked list.
>
> I *should* be able to split that FAT slice up into a primary for 7.2 and an
> extended partition that will hold CentOS' other partitions; however:
>
> In Googling about this, I have read some dire warnings about FreeBSD being
> unable to understand logical partitions; apparently installing FreeBSD
> *before* an extended partition will result in all your logicals getting
> trashed.  One is advised to put all the FreeBSD MBR partitions *after* the
> extended partition.
>
> Is that the case?  Have you any advice for me?
>
> One more thing: if it's possible, I'd like for the /home directory to be
> shared between both of my FreeBSD installations.  In a normal installation,
> there is a real /usr/home directory, with /home being a symbolic link.
>
> If I'm running FreeBSD out of one MBR partition (or slice), can I mount a
> directory that's in a different one?
>
> Thanks for your help!
>