What do you think ?: How should pseundo terminals behave ...

[Brandon S. Allbery KF8NH]

On Sep 26, 2006, at 14:09 , Magnus Ringman wrote:

> On 9/26/06, Brandon S. Allbery KF8NH <allbery at ece.cmu.edu> wrote:
>> I think that in many circumstances (and, as you note, implemented in
>> other OSes), the correct behavior *is* to treat hangup as "backing
>> device no longer exists" --- an older session should not leak into a
>> newer one, it is a potential security hole and certainly a potential
>> source of confusion.  And if hardware ttys do it, I should think
>> virtual ones should also do so for consistency.
>
> Methinks Sir has it the wrong way around!
> Hangup on a hardware device -doesn't- void a program's access to the
> device.  It just (optionally) sends the process a SIGHUP.  That is why
> somebody (iirc, for SunOS < 5) invented vhangup(2) as a means for a
> new session owner to insure it was the only process using the
> terminal.

I think you misunderstood:  yes, physically you do not lose access,  
but for security reasons *logically you should*, and that is why  
vhangup() was invented.  And, this being done, it is also a  
reasonable --- and, more to the point, consistent --- model for what  
happens when a pty slave loses its master (which *is* equivalent to  
physically losing access).

-- 
brandon s. allbery    [linux,solaris,freebsd,perl]     allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH