Re: top delay value

> > typing "while :; do :; done". There are a thousand ways

No. What I write above is not a "fork bomb", it's a single
process which is wasting CPU in a busy loop. It's exactly
equivalent to top(1) with zero delay, except that top
produces some output, while a busy loop does nothing useful
at all.

I tested different shells and I found out that an exlicit sub shell
is required to let the shell fork:

while :; do (:); done

By the way, you can "emulate" top(1) with run ps(1) in a
shell loop like this (sh/zsh/ksh/bash syntax):

while :; do clear; ps -a; sleep 1; done

Do get zero delay, simply remove the sleep command from the
loop ... That's actually _worse_ than top(1) with zero
delay, because kernel cycles are wasted for the fork() and
exec() calls, not to mention I/O and other syscalls. An
empty shell loop ("while :; do :; done") doesn't perform
any syscalls into the kernel.

Bottom line: Disabling zero-delay in top doesn't buy you
anything at all. In fact, it might cause your users to
invent work-arounds (for example shell loops) that waste
even more resources.

So I have to limit the CPU time in /etc/login.conf and

:cputime=300:\

invoke cap_mkdb /etc/login.conf.

--
"Feel free" - 5 GB Mailbox, 50 FreeSMS/Monat ...
Jetzt GMX ProMail testen: http://www.gmx.net/de/go/promail
_______________________________________________
freebsd-hackers@xxxxxxxxxxx mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-hackers
To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@xxxxxxxxxxx"