Okay, okay, mea culpa, this is an OS/X question ... but, maybe someone here will know.

I have an OS/X (Snow Leopard, HFS Journaled) external disk with a corrupted journal. The drive will not mount. Disk Utility repair identifies "invalid contents in journal," runs for several hours, finishes promising that the disk is repaired. But it won't mount, and when Repair is run again, the same "invalid contents" message is repeated.

Since Disk Repair does run, I'm confident that the data is still there ... and that the drive works. But I can't force past the apparent journal problem. diskutil removejournal force does not succeed. (Yes, even with "force." I get some "error -9972.")

So far, all of the things I've done have been interactively, i.e. not in single-user mode. However, this drive is not the boot drive: it is external.

"Googling around," I find various discussions ... from 2005, 2007 and such ... and assorted people hawking this-or-that third party tool. What I really can't find is current information on this problem. (Now, admittedly, Snow Leopard is quite a few years old now.)

Assuming that you are talking to "a Unix/Linux nerd," who will know-how to drop into single-user mode (if need be) and so on ... can someone give me or point me to current information about how one might proceed? I think that what I need to do here is basically to force OS/X to remove or replace that journal . . .

I cannot provide any info on how to repair the journal, but I have succesfully mounted several supposedly "broken" hard drives in OS X using a gParted Live, or System rescue CD. (See below):
http://s22.postimg.org/yo7zbt5hd/DSC_0320.jpg

Then from there I have been able to do a full backup of the contents of the broken drive under OS X to a new drive.

Not, I realize, an answer to your question, but in my experience the OS X Disk Utility is crap, and why on earth the original OS (OS X) cannot mount the "broken" drive when GNU/Linux can is... strange, to say the least.

PS. I should have written down the mount command for mounting hfs+ disks, since it is impossible to remember, but it is out there on the Internet! DS.

Yeah, hoping to find an OS/X-based solution in this case. The catch-22 is that disk repair (which is basically the Unix fsck command in comfy Cupertino drag ...) says that it has repaired the drive, but it didn't. Exactly the same journal message appears. Furthermore, when you ask to turn-off journaling (I see no command, "delete the journal contents") even "force" does not work. There should be a way to get this job done with Mach commands . . . :-[

And there even have been suspiciously promising reports of success, e.g. http://www.practiceofcode.com/post/7...d-disk-journal . . .

I know, I have seen that too under OS X. Like I said, I have NEVER been able to repair a disk properly with OS X's Disk Utility.
I have ended up doing as above: saving the content with GNU/Linux, and switch to a new drive. If you find a way, I would be delighted to learn how you did it.

Side note: it is rather odd how often the drives die on the Apple computers (we use them at work), despite them supposed to being "high end" and rather pricey.

Well when a partition craps out on Mac Os X none of their utilities (graphical or command line) is able to repair it in most cases (even when the disk is fine hardware-wise). I even tried to repair with the Linux tools but gave the same results.

One thing you must check - the SMART status of the problematic drive. If you have either "Reallocated Event Count", "Current Pending Sector Count", "Reallocated Sector Count" non-zero raw value, the disk is probably about to crap out.