When I decided to reformat and install my Mac Mini with the latest testing version of Debian (lenny, at the time of this writing) I discovered that I couldn’t mount my HFS+ OS X backup drive with write access:

erin:/# mount -t hfsplus /dev/sda /osx-backup
[ 630.769804] hfs: write access to a journaled filesystem is not supported, use the force option at your own risk, mounting read-only.

This warning puzzled me because I was able to mount fine before the reinstall and, since the external drive is to be used as the bootable backup for my MBP, anything with “at your own risk” was unacceptable.

I had already erased my previous Linux installation so I had no way of checking what might have previously given me write access to the HFS+ drive. A quick apt-cache search hfs revealed a bunch of packages related to the HFS filesystem. I installed the two that looked relevant to what I was trying to do:

hfsplus - Tools to access HFS+ formatted volumes
hfsutils - Tools for reading and writing Macintosh volumes

No dice. I still couldn’t get write access without that warning. I tried loading the hfsplus module and then adding it to /etc/modules to see if that would make a difference. As I expected, it didn’t. I was almost ready to give up but there was another HFS package in the list that, even though it seemed unrelated to what was trying to do, seemed worth a shot:

hfsprogs - mkfs and fsck for HFS and HFS+ file systems

It worked! I have no idea how or why (and I’m not interested enough to figure it out), but after installing the hfsprogs package I was able to mount my HFS+ partition with write access.

Update:

As Massimiliano and Matthias have confirmed in the comments below, the following solution seems to work with Ubuntu 8.04:

From Linux, after installing the tools suggested before, you must run:
mount -o force /dev/sdx /mnt/blabla

Otherwise, in my fstab, I have an entry like this:
UUID=489276e8-7f9b-3ae6-8c73-69b99ccaab9c /media/Leopard hfsplus defaults,force 0 0