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└─⟦a0efdde77⟧ Bits:30001252 EUUGD11 Tape, 1987 Spring Conference Helsinki
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Submitted by: ihnp4!utzoo!hcr!hcrvx1!hugh
Mod.sources: Volume 7, Issue 90
Archive-name: forktest


[  This program is designed to be called by programs that allow
   shell escapes.  It prints out the argc,argv parameters, and
   lists the disposition of signals, alarm calls, etc.  The fun
   part is when it lists the open file descriptors...  -r$ ]

I would like to submit the following program to mod.sources.  I hope
that the comments are sufficient explanation.  I don't see that a
manual is worthwhile.

I have run this program under System V and Version 7.  I have not
tested it under BSD, but I know of no impediment.

With this program, I have found bugs in a number of UNIX System V
utilities.  I am sure that BSD programs would be just as buggy, but
I haven't tested them.  Here are some examples:

Programs that leave extra file descriptors open:
     sdb ! command
     mailx ~! command during message composition, and ! command (two extra)
     mail ! command
     rn ! or | command (5 extra!)
     cu ~! command (one extra: number 5)

Programs that leave signals ignored:
     mailx ~! command (SIGINT!)
     rn ! and | commands (SIGEMT!?)

I think that this list shows that it is easy to get fork(2) wrong.
I hope programmers will use ForkTest to catch this type of bug
early.  Exercise for the reader: what can you scribble on with those
extra file descriptors?

Hugh Redelmeier (416) 922-1937
utzoo!hcr!hugh