"Custom Access" permissions are locking me out of my own computer!

Question

"Custom Access" permissions are locking me out of my own computer!
I have a Mac Book Pro which I can no longer access, due, I believe, to a problem with disk and file permissions. When I attempt to open up the volume, which I am able to put in FireWire target mode and mount on the desktop of a nearby iMac G5, I get an error message saying: "The folder 'MacBook Pro' could not be opened because you do not have sufficient access privileges."
When I select the 'MacBook Pro' volume and run the Get Info command, I learn that the system, admin, and everyone else groups now have "custom access." I suppose that this newly acquired "custom access" is the reason that the volume icon now appears on the desktop with a lock at its lower left corner! Unfortunately, that lock is keeping me out, so I need help in finding the key back in!
How all this came about overnight is a mystery wrapped in a enigma similar to my getting pneumonia last summer. Coming down with both diseases would require telling long stories that would only have as their common objective the desire to be cured. I might have gotten the pneumonia at my college reunion; my laptop computer might have caught a cold last night when I ran TechTool Pro and optimized my volume prior to installing its eDrive today. Or, my laptop computer may have choked when I tried to add Disk Warrior to the TechTool Pro eDrive and inadvertently issued some command that resulted in my normal permission settings getting changed and rendering everything on the computer completely inaccessible to me. Who knows for sure? Right now, the cause doesn't matter: finding the solution does.
I used TechTool Pro to run a series of tests before (and after) I got locked out of my own computer and the volume passed all the tests for volume integrity and file integrity. TechTool also rebuilt the directory, defragged all the files, and optimized the hard drive into one, large, well-organized segment of files --that I unfortunately can no longer access!
*What I think I need now are some very explicit, error-free, Terminal (UNIX) instructions telling me how to change the permissions on an external FireWire volume called "MacBook Pro" containing Leopard Mac OS X 10.5.7 from its current custom access privileges back to my settings before my poor computer caught this disabling cold.*
I do have a SuperDuper clone of this MacBook Pro computer on an external FireWire, which I could probably use to relieve me of my pain. But, if at all possible, I would like to call upon that option only as a last resort for two reasons:
(1) I am not entirely comfortable that the clone is completely reliable at this moment. My last cloning operation last night (before this corrupted permissions problem occurred) did not complete itself, leaving the cloned volume in an unknown, or unstable, state. (2) I would like to use this problem as an opportunity to grow and learn more about the Terminal and UNIX commands.
I have read the relevant sections in David Pogue's missing manual on Mac OS X Leopard, so I am familiar (in theory) with the concepts he explained regarding ownership, file permissions, the root, Terminal, the CHMOD command, and the SUDO command. It's just that, considering the awesome power of the SuperUser Do command, I'm not all that confident yet that I could write the command(s) that could affect the state of my entire computer hard drive. So, *I'm asking for guidance from a UNIX guru to guide my hand this first time out.*
I know about the idea of safe booting up as a single user, but since I do have my laptop computer mounted on the desktop of my iMac as a Firewire volume, I would prefer to use Terminal on the iMac to fix the permissions on that mounted volume, called "MacBook Pro".
*Experts only, please*. Theories about what might have caused this problem would be nice, but what I really need is explicit command line code to cure this one. Since other people may occasionally encounter this problem of being locked out of their own computer, it would be fine with me if some knowledgeable guru wants to use this as a springboard to write a detailed tutorial on the topic along the way to the solution. Thanks.
bowlerboy_jmb

Answer 1

{I read that article you sent me to, Baltwo, but it does not seem appropriate, because the disk is not invisible. It's locked! I also went through all the discussions on flag changing you directed to me to look up, and I tried to apply something from there to my situation. But that's not working for me yet either. The topics there seem to be close enough to be relevant to my case, but none are exactly on the mark, and so far they deliver no cigar. Maybe I missed the one thread you had in mind from among the twenty I looked through: I can't be sure. You point it out, if you have one in mind. Anyway, in the absence of anyone providing me with specific Unix code or suggestions about my particular situation, I plunged ahead on my own, and I attempted to write some Unix code that might fix my problem. So far, I've had no success. This posting intersperses my comments along with the lines of Unix code which were displayed on my MacBook Pro during my recent attempts to tinker under the hood. My remarks are contained inside of curly brackets like { and } while the results of my Unix experimenting in Single User Mode on the laptop are presented without curly brackets. These were initially notes to myself, so I'm creating a post around my Unix dabbling to see if it triggers any feedback, corrections, and guidance for moving ahead. I'm stuck right now.}
date
Fri Jun 19 17:52:25 EDT 2009
:/ root# sudo chflags nouchg /
sudo: can't open /private/etc/sudoers: Permission denied
:/ root# sendmail: warning: valid_hostname: empty hostname
sendmail: fatal: unable to use my own hostname
:/ root# ls -l
{The screen filled up with rows of file names and their permissions, like...}
drwxrwxr-x+ 43 root admin 1462 Jun 16 04:36 Applications
:/ root# exit
{Nothing happens for quite a while, then...}
jettisoning kernel linker.
{...and then several lines of replies fill up the screen, ending in that same loop regarding no such file or directory found, in regards to mDNSResponder. I had tried the {chmod 775 > solution recommended by a user at a web site I Googled to deal with the mDNSResponder problem he had. The chmod 775 / command worked for him, he reported, but it does not succeed for me. The mDNSResponderline continues to repeat itself ad infinitum, so I must force the Mac to turn off by holding down the power button for several seconds. Upon restart in Single User mode, I observe that, as before, "Root device is mounted read-only," so this time I try to amend permissions at the root level with...}
:/ root# sudo chmod 755 /
{If I understand what I've just learned about Unix, this tells the Mac to give me permission to do anything, but to give all others permission only to read and execute. Unfortunately, the command fails. The computer again responded with the same lines that it gave me when I had issued the command regarding no user flags, namely:}
sudo: can't open /private/etc/sudoers: Permission denied
:/ root# sendmail: warning: valid_hostname: empty hostname
sendmail: fatal: unable to use my own hostname
{So, to summarize, I have a MacBook Pro which I am apparently locked out of and cannot change. The hard disk is not invisible: it will appear as an external drive when placed in Target Mode and connected via a Firewire cable to an iMac. I tried to use Terminal on that iMac to change permissions on the MacBook Pro, but permission was denied.
{So, I have tried to make changes on the MacBook Pro directly. I learned that it will neither start-up under normal circumstances nor via Safe Boot mode. It will, however, start-up under Single User mode. Based on my bleary-eyed crash course in Unix throughout all of last night and early this morning, I did gain some additional understanding about UNIX from some [free online books|http://www.scribd.com/doc/12747795/Made-Easy-Unix-for-Beginners] and articles, especially from a thorough and lucidly written article at Indiana University called [In Unix, how do I change the permissions for a file?|http://kb.iu.edu/data/data/abdb.html]
{Also, I followed the links to the Apple discussions on user flags, and I cherry picked the most appropriate solutions suggested there to see if they will apply to my situation. However, none quite fit. None have thus far succeeded. I think I now know how to formulate the syntax of Unix commands in regards to modifying permissions, and I'm willing to plow ahead and try things out. But I'm only a rank beginner in this Unix realm, so maybe I'm doing something wrong in that department.
{It just boggles my mind that someone can inadvertently be locked out of their computer without a way back in, so all I'm asking for is some trouble-shooting guidance to find the key back in. Anyone got it? Is this a problem that can be cured by writing some Unix commands to the system? Or, does the solution lie elsewhere?}
bowlerboy_jmb