How can I change 'Custom' permissions for TM backup disc?

Time Machine uses special "deny everybody everything" permissions. You should not change them.

FIrst, do a +Repair Disk+ (not permissions) on the TM volume via DIsk Utility (in your Applications/Utilities folder).

If that doesn't correct it,

If you only have a partial backup, or don't need the ones you've done, the simplest thing to do is just erase the disk/partition.

If you don't want to erase it, here's a workaround:

First, you need to find the name of the hidden file that's causing the problem Click here to download the +Time Machine Buddy+ widget.

It shows the messages from your logs for one TM backup run at a time, in a small window. If it shows a message like this: "You do not have appropriate access privileges to save file “.<nnnnnnn>” in folder <Name>"* skip to *Open the Terminal App* below.

If not, Click here to download the +Tinker Tool+ app. It allows you to change the Finder to show hidden files (among many other things). Select the first option under Finder, then click +Relaunch Finder+ at the bottom. Reverse this when done.

In a Finder window, select your Time Machine drive/partition. The very first file shown should have a name consisting of a period (dot) followed by 12 numbers and/or letters. (This is your Mac's Ethernet address). Copy or make a note of it.

Open the Terminal app (in your Applications/Utilities folder).

In Terminal, the prompt looks like this: user-xxxxxx:~ <your name>$

(where <your name> is your short user name). It's followed by a non-blinking block cursor (unless it's been changed via Terminal > Preferences).

At the prompt, type the following exactly as shown, substituting the name of your TM drive exactly, including any spaces, between the quotes; and the string of numbers & letters from the message where the series of x's are (keep the dot):

<pre> sudo chmod 644 /volumes/"TM drive name"/.xxxxxxxxxxxx</pre>
example: sudo chmod 644 /volumes/"TM Backups"/.0a1b2c3d4e5f

Press Return. You'll get some warnings and a request for your Administrator's password. Type it in (it won't be displayed) and press Return again.

Then try a +Back Up Now+ from the TM icon in your Menubar, or by control-clicking (right-clicking) the TM icon in your dock.

Living Fossil wrote:

1. If I can't even open the disk (wrong access privileges, even tho I'm the Administrator), how can I erase it?

You can't open it via Leopard. But you can erase it via Disk Utility.

2. If I do erase it before relaunching Time Machine, I am taking a big risk with the data on my iMac which has been behaving erratically lately - perhaps I had better find another disk to do an emergency backup on.

Yes, by all means.

3. I had already read that I ought to repair the disk with Disk Utility, but when I examined it, DU reported that it "appears to be OK". If I now repair it, will DU do anything?

No, unless something else has happened in the meantime. But it won't hurt anything, either.

Living Fossil wrote:
I am now back in my original location and I've done a repair on my TimeMachine disk as suggested, and a complete permissions repair on my iMac (took nearly four days!!!). I am now trying to take your advice about using TinkerTool, but sadly it downloads and unpacks but won't launch (gives an error:
-10822).

That's a first, too.

Ok, we'll use the Terminal app instead. Copy and enter the following in a Terminal session (as above):

defaults write com.apple.finder AppleShowAllFiles TRUE

Then restart the Finder (Apple Icon > Force Quit > Finder > Relaunch).

(When done, use the same command, but with FALSE instead of TRUE, to hide them again.)

That should make all invisible files visible. Use the procedure above to get the string of numbers and letters, to substitute for the xxxxx's.

I fear for my photo archive which would be left un-backed up on my obviously dodgy iMac, unless I can find a lot of space on another disk (not easy where I am). Also I would very much like to understand what all this trouble is about.

Agreed. Something is (or has) gone rather wrong. Whether your OS is corrupted, or your internal HD is beginning to fail, or something else, what you're seeing is not normal.

If these are your only backups, I'd strongly suggest getting another drive for a separate set of backups, that you can store in your safe deposit box, workplace, relative's house, etc. That way, you're also protected against fire, flood, theft, direct lightning strike on your power lines, and the like. Many people have two drives; they use one for a week or so with TM and/or a "clone" app, then take it off-site and swap with the other one.

At a minimum, archive them to DVDs.

Living Fossil wrote:
First, thanks for sticking with me and for answering so quickly! However, we are not out of the wood yet. I did the stuff with Terminal but I can't look at my backup disk because when I try to open it (double-click) I get 'The folder "WHCbackup" could not be opened because you do not have sufficient access privileges'. I think I mentioned this at the beginning, but of course I have done various repairs since then.

It's the same thing.

I can work out my machine's MAC address from the System Prefs. Could I use that (presumably without the colons) to carry out your instructions?

You mean System Profiler? Yes, that should get it.

This happened to me as well, I stupidly tried to give my user account read and write permissions on everything but in the process removed the other user accounts permissions. Anyway, I cleared that all up but I began having the same problem that you were having with my time capsule.
I archived and erased the TC disk but that didn't work so I phoned up apple and they said to verify and repair disk in disk utility, I'm in the process of doing that now and I'm waiting to see how it went.

Living Fossil wrote:

However I am not sure why you describe giving your user account read and write privileges as 'stupid'? It SEEMS logical, and there are no warnings against it. I think here Apple have let down the "computing for the rest of us" ethos, just as they have with networks ("ask your administrator" for Heaven's sake - is this Windows?). Since permissions are so mysterious (what are they for and why do they go wrong so easily?) I wonder why we need them at all. I am exploring this on another thread and it looks like I'm getting some help.

I can't answer in general, but as far as the permissions on your Time Machine backups (that started this thread), Time Machine uses special "deny everybody everything" permissions, in an attempt to keep us mere mortals from messing with the backups. The structure and special "multi-links" it uses to work it's "magic" are very different from normal files and folders, and can easily be damaged by using the Finder to move or change anything.

Your initial problem was likely caused by a glitch introduced in an earlier version of Leopard, affecting a single critical hidden file on your TM disk. There is a fix for it, although just erasing the disk works, too.

Here's some info on the "works" of Time Machine: http://www.appleinsider.com/articles/07/10/12/roadto_mac_os_x_leopard_timemachine.html
and: http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/14