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From: rjk@sawmill.sawmill.uucp (Richard Kuhns)
Newsgroups: comp.unix.wizards
Subject: Re: Phantom CPU gobbler?!
Message-ID: <RJK.90Jul9162817@sawmill.sawmill.uucp>
Date: 9 Jul 90 21:28:17 GMT
References: <960004@teecs.UUCP> <1277@tuewsd.win.tue.nl>
Sender: news@sawmill.uucp (News Administration)
Organization: Grauel Enterprises
Lines: 56

In article <1277@tuewsd.win.tue.nl> wsinpdb@lso.win.tue.nl (Paul de Bra) writes:
   Sender: wsinpdb@win.tue.nl (Paul de Bra)
   Organization: Eindhoven University of Technology, The Netherlands
   Lines: 15

   In article <960004@teecs.UUCP> belkin@teecs.UUCP (Hershel Belkin) writes:
   >...
   >Every so often I fins a shell process (sh or ksh) which has somehow
   >become dis-associated with its logon session.  By this I mean that
   >the shell's PPID is "1", and the user is no longer logged on.
   >...

   This is the infamous trap/signal/eof bug, which I don't know exactly,
   but some combination of trapping and sending signals and having
   end-of-file on standard input causes an infinite loop in the Bourne
   and Korn shell, at least in some Unix versions which haven't fixed the bug.

   Anyone know the full scoop?

   Paul.

I don't know if this is the *full* scoop or not, but some versions of Korn
shell and Bourne shell have problems if a program leaves the terminal
(stdin) in non-blocking mode when you've set `ignoreeof'.  The following
little program will exercise this bug, if that's what it is.


Rich Kuhns
newton.physics.purdue.edu!sawmill!rjk
==============================cut here==============================
/* killksh.c */
#include <stdio.h>
#include <fcntl.h>

extern	int	errno;

main(argc, argv)
     int	argc;
     char	*argv[];
{
    char	*progname;
    int		flags;

    progname = *argv;
    if ((flags = fcntl(0, F_GETFL, 0)) < 0) {
	fprintf(stderr, "%s:can't get flags (errno=%d)\n", progname);
	exit(1);
    }
    if (fcntl(0, F_SETFL, flags|O_NDELAY) < 0) {
	fprintf(stderr, "%s:can't set flags (errno=%d)\n", progname, errno);
	exit(1);
    }
    fprintf(stderr, "shell should crash in 3 seconds\n");
    sleep(3);
    exit(0);
}