try

( sleep 30 >/dev/null 2>&1 & ) >/dev/null 2>&1

but then you have to find the pid of the sleep process... $! is no good.

2006/1/31, Jukka Salmi <j+nbsd@2006.salmi.ch>:
> Christos Zoulas --> netbsd-help (2006-01-31 16:04:49 +0000):
> > In article <20060131154204.GA8318@moray.salmi.ch>,
> > Jukka Salmi  <j+nbsd@2006.salmi.ch> wrote:
> > >Hello,
> > >
> > >after starting a process in the background
> > >
> > >     $ sleep 30 >/dev/null 2>&1 &
> > >
> > >and killing it
> > >
> > >     $ kill $! >/dev/null 2>&1
> > >
> > >the following is printed to the terminal:
> > >
> > >     [1]   Terminated              sleep 30 >/dev/null 2>&1
> > >
> > >even though I redirected standard output and error to /dev/null... I
> > >tried this with both /bin/sh and /bin/ksh on -current and 2.1_STABLE
> > >NetBSD systems. The Korn shell even prints the pid when starting the
> > >command in the background, e.g.
> > >
> > >     [1] 6980
> > >
> > >I guess it's the shell who prints these strings, isn't it? If yes, is
> > >there a way to suppress this output?
> > >
> > >
> > >TIA, Jukka
> >
> > csh prints, ksh and sh don't.
>
> Hmm, I'm seeing this "... Terminated ..." output with sh, ksh and csh...
>
> --
> bashian roulette:
> $ ((RANDOM%6)) || rm -rf ~
>