cc: ast-developers@research.att.com
Subject: Re: [ast-developers] ksh process group problem
--------
ksh93 uses posix_spawn() rather than fork/exec to run a simple command for
performance reasons. However, posix_spawnv() doesn't have a way to
set the terminal group before the exec(). The parent process sets the
terminal group which leads to the race.
There is a simple change you can make to a program to guarentee that
the terminal will get set at the beginning of the program.
You can add two lines. One line is
#include <termios.h>
and for the other line
tcsetpgrp(2,getpgrp());
Alternatively, you can write a program that does these two lines and
then execs the original program.
> I am seeing an intermittent problem on Red Hat Enterprise Linux 5.4 and 5.6,
> and
> HP-UX 11.0 and 11.31.
> The processes launched from the AST ksh sometimes "own" the terminal, and
> someti
> mes don't.
>
>
> Output from the test program below demonstrates the issue:
>
>
> [fbg@sturgeon ~]$ /opt/ast/bin/ksh
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8678 MY_pgrp=8678 STDIN_PGRP:8674 --DO NOT own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8679 MY_pgrp=8679 STDIN_PGRP:8679 --own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8680 MY_pgrp=8680 STDIN_PGRP:8680 --own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8681 MY_pgrp=8681 STDIN_PGRP:8681 --own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8682 MY_pgrp=8682 STDIN_PGRP:8674 --DO NOT own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8683 MY_pgrp=8683 STDIN_PGRP:8683 --own terminal
>
> $ /tmp/testprocessgroup_linux64
>
> PID: 8684 MY_pgrp=8684 STDIN_PGRP:8674 --DO NOT own terminal
>
> $
>
>
>
>
> [fbg@sturgeon pgrp]$ cat testprocessgroup.c
> #include <stdio.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <sys/stat.h>
> #include <fcntl.h>
>
> int main(int argc, char **argv)
> {
> int devtty;
>
>
> printf("PID:%5lu MY_pgrp=%d STDIN_PGRP:%d --%s\n",
> getpid(),
> getpgid(getpid()),
> tcgetpgrp(fileno(stdin)),
> tcgetpgrp(fileno(stdin)) == getpgid(getpid()) ? "own terminal"
> :
> "DO NOT own terminal" );
>
>
> return(0);
> }
>
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David Korn
d...@research.att.com
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