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Re: Question about file system permissions



Les Mikesell wrote:
On Tue, 2007-01-02 at 14:17 -0500, Joe Smith wrote:
Mikkel L. Ellertson wrote:
.... But as you have
noticed, it does not work out as well when editing shared files.
Oddly perhaps, Unix has never really provided shared writeable files.

What?  If you have write permission you can write.

But two processes writing to the same file at the same time gives you what? Probably not what you want.

I don't mean literally Unix can't do it, I only meant that Unix never really supported it with a standard API that worked well enough to be widely accepted and handled all the complicated corner cases that rear up when two users want to naively "share a file".

Perhaps there are good theoretical reasons for it; perhaps it was just one of those simplifying assumptions that Unix was born with, I don't know.

Initially there was no file locking and the only really atomic
operation was creating a file or making a hard link to an existing
file.  Later, about a dozen different file locking methods were
added and the applications never really converged on how to do
it across versions and network mounts.  Plus, a lot of stuff depends
on the unix filesystem semantics ...

Thanks for making my point with real facts ;-)

Sorry everybody: drifting off-topic and talking stuff that I know just well enough to make an ass of myself, so I'm going to shut up right about... now.

<Joe


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