I have nTop 3.2 on FreeBSD 6.0. The --pcap_setnonblock option was
enabled by default in the ntop.sh script. The man page says it will
cause high cpu load, but "it does not actually interfere with other
work". However, it was causing problems for the netflow plugin. The
RECV queue for the netflow UDP port was always around 40K and I was
dropping a LOT of netflow packets. After restarting without this option
enabled, everything looks to be working much better.
I guess the main question I have is, if "THIS OPTION IS OFFICIALLY
UNSUPPORTED and used at your own risk", then why is it enabled by
default?
Thanks!
Gary
--pcap_setnonblock
On some platforms, the ntop web server will hang or appear to
hang (it
actually just responds incredibly slowly to the first request
from a
browser session), while the rest of ntop runs just fine. This
is known
to be an issue under FreeBSD 4.x.
This option sets the non-blocking option (assuming it's
available in
the version of libpcap that is installed).
While this works around the problem (by turing an interupt
driven
process into a poll), it also MAY signifcantly increases the
cpu usage
of ntop. Although it does not actually interfere with other
work,
seeing ntop use 80-90% or more of the cpu is not uncommon -
don't say
we didn't warn you.
THIS OPTION IS OFFICIALLY UNSUPPORTED and used at your own
risk. Read
the docs/FAQ write-up.
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