Sharing disk space between MacOS X and Linux
Hi,
I spent a few hours figuring out how to do this so I thought I'd share the
results of my fiddling to save people time in the future.
I have an iBook2 on which I primarily run Linux. However, on occasion I reboot
into MacOS X -- primarily to watch a DVD or connect to the Internet using the
built-in 56K modem. For various reasons it is desirable to have a partition
which both operating systems can use (to exchange downloaded files, etc).
Originally I planned to have a 1.5Gb HFS+ or HFS partition shared between the
two. However, this didn't work out -- the hfsplus tools don't really "mount"
the partition into the kernel's VFS tree and the vanilla HFS driver has
crashed my kernel several times. So I scrapped this idea and the partition lay
fallow for a few months. A few days ago, however, I was away from my Ethernet
and wireless networks and urgently needed to download a large postscript file
to the Linux partition using the 56K modem, so I went looking for a solution.
It occurred to me that both OS X and Linux 2.4 have pretty solid support for
FAT32. I could reformat and use my 1.5Gb "shared" partition as FAT32 under
Linux quite happily using 'mkdosfs -F 32' and mounting it with the vfat
filesystem. Lovely. Indeed, I could mount the same partition under MacOS X
from the shell, however I couldn't persuade MacOS to automount it and make it
appear on my desktop, because OS X thought it was an HFS partition without a
correctly formatted HFS volume due to its type entry in the partition map.
Much fiddling later I discovered the solution: Mac OS X will discover and
mount the partition correctly as FAT32 if you set the partition type to the
magic string "DOS_FAT_32". In mac-fdisk, use the 'd' to delete your partition,
then use the 'C' (capital C!) option to create a new one covering exactly the
same sectors on the disk, then enter the type as "DOS_FAT_32". I partitioned
under Linux and then formatted under OS X using the Disk Tool in Utilities.
It works very well indeed for me. Under Linux the fstab entry looks like this:
/dev/hda10 /scratch vfat defaults,uid=500,gid=500 0 0
... and 'mac-fdisk -l' reports:
/dev/hda
# type name length base ( size ) system
dump: name /dev/hda len 8
/dev/hda1 Apple_partition_map Apple 63 @ 1 ( 31.5k) Partition map
/dev/hda2 Apple_Driver43 Macintosh 54 @ 64 ( 27.0k) Driver 4.3
/dev/hda3 Apple_Driver43 Macintosh 74 @ 118 ( 37.0k) Driver 4.3
/dev/hda4 Apple_Driver_ATA Macintosh 54 @ 192 ( 27.0k) Unknown
/dev/hda5 Apple_Driver_ATA Macintosh 74 @ 246 ( 37.0k) Unknown
/dev/hda6 Apple_FWDriver Macintosh 200 @ 320 (100.0k) Unknown
/dev/hda7 Apple_Driver_IOKit Macintosh 512 @ 520 (256.0k) Unknown
/dev/hda8 Apple_Patches Patch Partition 512 @ 1032 (256.0k) Unknown
/dev/hda9 Apple_HFS untitled 5120000 @ 1544 ( 2.4G) HFS
/dev/hda10 DOS_FAT_32 Scratch 3072000 @ 5121544 ( 1.5G) Unknown
/dev/hda11 Apple_Bootstrap Bootstrap 65536 @ 8193544 ( 32.0M) NewWorld bootblock
/dev/hda12 Swap Linux 2097152 @ 8259080 ( 1.0G) Unknown
/dev/hda13 Apple_UNIX_SVR2 Linux 28713848 @ 10356232 ( 13.7G) Linux native
I'm very pleased with this. The only annoyance is that OS X insists on
labelling the disk icon "SCRATCH" and won't allow me to rename it to something
that isn't all-caps. Ho hum, can't have everything ;)
I'd be interested if anyone has solved this problem by a more elegant route
(preferably involving a "real" filesystem...)
Will
_________________________________________________________________________
William R Sowerbutts will@sowerbutts.com
Coder / Guru / Nrrrd http://sowerbutts.com
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(m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}
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