[TriLUG] dual boot and partition access

[Kevin Hunter]

At 10:18pm -0400 Tue, 29 Mar 2011, Michael Rulison wrote:
> Imagine:
> partition 1 ubuntu / root; /home/user; and all the rest -- but with v.
> little of my own in /home/user [bootable]
> partition 2 ubuntu /linux-home --- where I have copied the above
> /home/user and have lots of my own files.
> partition 3 winXP with lots of pgms and data files. [bootable]

It may be more helpful to talk in conceptual terms of 'partitions', 
'filesystems', and 'mount points'.  First, there's the physical bits 
layout, or partitions.  Lets assume you have a 100GiB HDD, partitioned thus:

part1  10 GiB
part2  40 GiB
part3  50 GiB

This partitioning scheme does not yet give a notion of OS usage or 
filesystem formatting.

The second concept of a filesystem says what scheme you'd like to use to 
keep the data bits organized and usable on each partition.  For both 
operating systems to be able to utilize a filesystem (which you 
currently happen to be housing on a partition), they'll both need to 
have a driver that understands the filesystem in question.

As an example, since both Windows and Linux have drivers for the fat32 
filesystem, you /could/ format each of the above as:

part1  (10 GiB)  fat32
part2  (40 GiB)  fat32
part3  (50 GiB)  fat32

Then both operating systems could read all three filesystems.  However, 
the more likely filesystem scheme might be something like below, noting 
that unless you were to install a program or driver in Windows, it will 
not be able to read the filesystem on part1.[1]

part1  (10 GiB)  ext4
part2  (40 GiB)  fat32
part3  (50 GiB)  ntfs

Finally, at the point you actually boot one of the operating systems, 
the decision of what to mount where is almost completely arbitrary.  The 
scheme that you have described, of mounting a separate HDD partition to 
/home is a very common scheme, and should work just fine.  So, with the 
use of the ntfs-3g drivers in Linux, you could mount each of the 
partitions to /, /home, and /windows:

part1  (10 GiB)  ext4   /
part2  (40 GiB)  fat32  /home
part3  (50 GiB)  ntfs   /windows

Your Linux install will transparently use part2's filesystem as /home, 
and will transparently let you use /windows.  You'll be none-the-wiser 
unless you were use 'df -hs'.  Windows, on the other hand, short of [1] 
below, will only see part1 as dead space on your HDD, and probably mount 
part2 as D:.  (I'm not a Windows person, so YMMV.)

> Question: If I 'move' my ubuntu /home over to /linux-home (as the
> partition is registered) and make it my ubuntu /home directory
> (really), will WinXP still be able to 'see', read/write to
> /linux-home partition as it currently can?

To actually answer your question: as long as you do *not* use a 
filesystem for which Windows does not have a driver, Windows will see no 
change.  Or, put differently, if Windows can read/write to it now, and 
since you're /only/ changing information in /etc on part1, Windows 
should have no clue that you've done anything, short of random files 
that will appear and disappear between Windows boots as you add and 
delete them while in Ubuntu.

HTH,

Kevin

[1] http://www.howtoforge.com/access-linux-partitions-from-windows