Can remote users control the scanner(s) too?

J.B. Nicholson-Owens jbn at
Wed Sep 29 06:43:53 UTC 2004

Oliver Grawert wrote:
> why should someone (for whom you would indeed have to set up an account
> before) want to use a scanner remote ??

Under ordinary situations with cooperative people, they wouldn't use a scanner 
remotely.  The trouble is, people aren't always cooperative and proper system 
administration should make the scanner available only to the person at the console.

The problem here is more along the line of a denial of service.  If a user is 
in the scanners group they can run a program which could do something with the 
scanner (such as scanning) and that program will work.  For a user at the 
console, this is fine.  For a user not at the console, this can be bad because 
remote users would effectively make the scanner unavailable to the person at 
the console.  I think most people consider scanners something used only by the 
person at the console, not any of the other users accessing their account remotely.

In a followup to my question, Nathaniel McCallum said that a system call would 
be needed to do this in the right way.  I'm guessing that a revoke() system 
call would be better than a shell script that adds the just-logged-on console 
user to the scanner group (and another shell script that removes the 
just-logged-off console user from the scanner group) because shell scripts 
wouldn't prevent someone from logging out at the same time as they launch a 
background process which hogs the scanner, thus preventing the next user at the 
console from using the scanner.

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