Encrypted home partition accessible by administrator

Bret Busby bret.busby at gmail.com
Mon Apr 22 18:13:47 UTC 2019

On 22/04/2019, Karl Auer <kauer at biplane.com.au> wrote:
> On Mon, 2019-04-22 at 12:04 +0100, Colin Law wrote:
>> chmod .
>> is not a valid command.  With
>> chmod 0 .
>> and
>> chmod 7 .
>> sudo can still be used to access the files.
> Perhaps Bret's memory is of an administrator misusing some variant of
> "chmod -R 0 .*"
> Don't test that command, by the way!


The operating system was UNIX System V. I think it was SCO UNIX System
V. It was somewhere in the late 1980's to early 1990's. I think, from
memory, it was running on a Unisys system.

It was simply a case of a student in a UNIX operating systems unit
class, entering the command
chmod .
which caused the loss of the account, as the superuser, in addition to
everyone else, was shut out of the user's home directory, and could
not see it to access it, anymore. A new account was created for that
student, and, we were warned to be careful, when using the chmod
command. In that unit, amongst other things, we were taught the
different shells, how to configure prompts (including how to get the
timestamp included in the prompt, how to use vi, how to fork and kill
processes, recursive commands, how UNIX and other systems deal with
paging, multitasking, with the different methods of multitasking
scheduling, etc, etc,etc. It was one of the OS units that I was taught
(and, now, mostly forgotten), at that institution. Another unit taught
DEC RSTS/e and a little RSX, from memory, and, some VAX/VMS, and the
networking between the different campuses, and, the different
networking archictectures.

It may be that the command, as I specified it, worked on SCO UNIX
System V, but does not work on Ubuntu Linux 1x.x. Maybe, Linux was
designed to prevent that occurrence And, this was probaly before Linux
kernel version 1. I think, from memory, somewhere around 1992, when
the local Linux User Group was meeting to announce the porting of
Linux to the 386, or, 486, the kernel number had not yet reached 1.
So, if
chmod .
does not work in Linux, and, is dismissed as an invalid command,
protection may have been inbuilt, to protect against the contingency.

But, it did work, in SCO UNIX System V, many years ago.

It is a bit like that famous (mythical ?) Microsoft voice recognition
demonstration, where a member of the audience is said to have yelled
out "Format see colon!", so the computer did.

So, no, as I said, the student entered the command
chmod .
on a UNIX system V system, and that caused universal loss of access to
the user's account, requiring a new account to be created for that

But, then, maybe this list has some hackers, who know more that UNIX
systems administrators at educational institutions, and, more than
some of the UNIX  (and other) operating systems lecturers, knew, back
then. It would not surprise me - in that class, were one or two
hackers, who were very advanced,in their UNIX skills, and, used their
hacking skills, to breach external systems, on occasion. They
apparently got caught and convicted. I understand that they did what
they did, more for amusement, than anything else. Their UNIX skills
left the rest of us, behind, so, they probably got bored.

Bret Busby
West Australia

"So once you do know what the question actually is,
 you'll know what the answer means."
- Deep Thought,
 Chapter 28 of Book 1 of
 "The Hitchhiker's Guide to the Galaxy:
 A Trilogy In Four Parts",
 written by Douglas Adams,
 published by Pan Books, 1992


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