Re: truss calls setpgid()

On Monday, October 11, 2010 9:17:19 am Ed Schouten wrote:
> Hi all,
> 
> I've been seeing this bug for a very long time, but I was too lazy to
> figure out the root cause earlier. It is TTY related, but in this case
> the TTY layer is not to blame. It does things correctly.
> 
> When you run a command in truss which calls ioctls on TTYs, it just
> locks up. This is because truss runs jobs in a separate process group.
> This also means you cannot send signals to it:
> 
> 	truss sleep 10000
> 
> Pressing ^C here won't work.
> 
> I've fixed it locally like this:
> 
> Index: usr.bin/truss/setup.c
> ===================================================================
> --- usr.bin/truss/setup.c       (revision 213113)
> +++ usr.bin/truss/setup.c       (working copy)
> _at__at_ -78,7 +78,6 _at__at_
>         }
>         if (pid == 0) { /* Child */
>                 ptrace(PT_TRACE_ME, 0, 0, 0);
> -               setpgid (0, 0); 
>                 execvp(command[0], command);
>                 err(1, "execvp %s", command[0]);
> 
> Question: was this intentional? I'd rather not break stuff.

It was added in the switch from procfs to ptrace(), but it's not clear why the 
child has a new process group.  It doesn't look like truss ever tries to kill 
the entire group for example.

-- 
John Baldwin