Date: Thu, 27 Apr 2000 17:50:20 -0700 From: Tim Kientzle <kientzle@acm.org> To: freebsd-bugs@freebsd.org Subject: Fix to CRON daemon... Message-ID: <3908E04C.1D7C42C9@acm.org>
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Some folks I work with found a problem in
BSDI's 'cron' daemon. This ultimately resulted
in the attached message from Paul Vixie; I notice
FreeBSD is also using Vixie cron.
- Tim Kientzle
-------- Original Message --------
> To: bsdi-users@bsdi.com
> Subject: Re: Cron setting SIGCHLD to SIG_IGN
> References: <200004271826.OAA23896@iridium.mv.net>
> In-Reply-To: mem@mv.mv.com's message of "27 Apr 2000 11:22:33 -0700"
> Date: Thu, 27 Apr 2000 14:47:02 -0700
> From: Paul A Vixie <vixie@mibh.net>
>
> mem@mv.mv.com ("Mark E. Mallett") writes:
>
> > Looking at the cron source code, I do see that cron is forcing
> > SIGCHLD to SIG_IGN for the children that it spawns. I'm afraid that
> > the reasoning behind this move escapes me.
>
> It's because cron (then called crond) was the first program I ever wrote
> that used signals or called fork or exec. This was in 1986, just after
> 4.3BSD came out, and well before signals had been posixified. signal(2)
> says, quite clearly:
>
> When a process which has installed signal handlers forks, the child pro-
> cess inherits the signals. All caught signals may be reset to their de-
> fault action by a call to the execve(2) function; ignored signals remain
> ignored.
>
> This means that having set SIGCHLD to SIG_IGN for my own purposes, I really
> needed (and apparently still need) to set it back to SIG_DFL before fork()'ing
> to run each command found in a crontab. Ouch! Sorry, all. Here's a patch
> against cron 4.0 (see ftp://ftp.isc.org/isc/cron/, since this is more recent
> than what ships with BSD/OS). The patch ought to apply, with some fuzz, to
> the shipping version.
>
> Index: do_command.c
> ===================================================================
> RCS file: /proj/src/isc/cvs-1/cron/do_command.c,v
> retrieving revision 1.4
> diff -u -r1.4 do_command.c
> --- do_command.c 2000/01/02 20:53:41 1.4
> +++ do_command.c 2000/04/27 18:45:37
> @@ -222,6 +222,13 @@
> chdir(env_get("HOME", e->envp));
>
> /*
> + * Since ignored signals remain ignored after fork()/exec(),
> + * we need to unignore our ignored signals before letting
> + * some unsuspecting user level command inherit them.
> + */
> + (void) signal(SIGCHLD, SIG_DFL);
> +
> + /*
> * Exec the command.
> */
> {
>
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