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Date:	Wed, 11 May 2011 09:34:25 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: GNU screen on Cygwin: Cannot seem to reattach, no matter what I try
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On May 10 15:07, Andrew Schulman wrote:
> > a session that I detached on the same tty just seconds before.
> > 
> > 3. chmod 666 on the socket file did not work (its permissions were 
> > already 644, owned my 'morse', as shown in my original session long).
> 
> No, I suggested that you try 0600, on the theory that your 0640 permissions
> might be too permissive, and screen would refuse to use the socket.
> Unlikely, but worth a try.
> 
> However, if your socket is on a FAT file system, I don't know if you can
> set 0600 permissions.
> 
> > HOWEVER, I am wondering: my Cygin /tmp *IS* on a FAT32 filesystem, *NOT* 
> > an NTFS filesystem.  Would that matter?  Are socket files properly 
> > handled by Cygwin on FAT32?  (I've never used a socket-based Cygwin 
> > program on this host before, at least not to my knowledge.)
> 
> Hm, that could explain it.  I don't recall this coming up before.

AF_LOCAL/AF_UNIX sockets are handled on all file systems.

But FAT/FAT32 have no provisions to store permissions like NTFS has.
Therefore the POSIX permission bits are only faked, 0755 for
directories, 0755 for files with the suffixes .exe, .lnk., and .com,
0644 otherwise.  If you chmod -r a file you get 0555 for .exe etc, or
0444 otherwise.

You can probably live with this if you can do without permissions on
files, but here's one of the cases where the application apparently
checks for permissions.  Same goes for many other security sensitive
applications.

My unofficial, very personal recommendation:  Don't use FAT/FAT32 unless
you really have to, for instance on USB sticks shared with embedded
gear.  Otherwise FAT/FAT32 is a crappy, unsecure, space-wasting file
system about as modern as the roman empire.  And you know, what have
the romans ever done for us?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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