hang on exit - bug or no bug?

Nicolas Williams Nicolas.Williams at ubsw.com
Sat Oct 6 04:01:42 EST 2001

On Fri, Oct 05, 2001 at 12:45:48PM -0500, Phil Howard wrote:
> Nicolas Williams wrote:
> > No, don't modify your OS' startup scripts, just run them differently.
> >
> > Look, the fds are left open, so you potentially lose data, but you don't
> > care, right? So why not run those scripts like so:
> >
> > ssh -n root at somehost /etc/init.d/syslog stop
> > ssh -n root at somehost /etc/init.d/syslog start \>/dev/null 2\>\&1
> I want to see the messages at startup that indicate why it didn't
> start, if that happens.  Of course the blame is that many daemons
> are not designed to do ths properly.  But the two that I am now
> designing/coding will be.  The servers will close the standard
> descriptors once it has determined the startup conditions are fine
> (of course later failures will have to go to syslog).

Don't forget to ALWAYS, ALWAYS open() something appropriate for stdio
after closing stdio; /dev/null if nothing else.

open("/dev/null", O_RDONLY);
open("/dev/console", O_RDONLY); /* or /dev/null */
open("/dev/console", O_RDONLY); /* or /dev/null */

Just in case any stupid library function you might use assumes that
stdio is a place to write error messages, or read from.

> > You have this issue with RSH too you know. I long ago learned to deal
> > with this by manually redirecting stdio to /dev/null. And yes, sometimes
> > you care about some bit of command's output, because you may want to see
> > error msgs from /etc/init.d/syslog, say. There's a few solutions:
> >
> >  - write a separate script for checking that the batch job is doing ok
> >  - use intr (yes, Solaris doesn't have one -- write one yourself) on the
> >    client side to set a timeout after which to kill ssh
> >  - write an intr-like command for the remote side that closes the fds
> >    after a timeout and which might be used like so:
> >
> >    ssh -n somehost somecommand 2\>\&1 \| iointr -t 30
> >  - fix the scripts
> - fix the daemons

Right. That's not always an option though... :)

> --
> -----------------------------------------------------------------
> | Phil Howard - KA9WGN |   Dallas   | http://linuxhomepage.com/ |
> | phil-nospam at ipal.net | Texas, USA | http://phil.ipal.org/     |
> -----------------------------------------------------------------


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