I'm surprised you are seeing such a high system load, and not CPU cycles
shown for nessusd.
I'm not clear if you are scanning and seeing these loads, or nessusd is
just waiting and you have high loads. If you are scanning and you have
high loads but you don't see nessusd taking CPU usage, I'd look for any
local firewall or IDS or other type of on-system resource that could be
making the kernel work a bit harder. If you are scanning just a few
hosts and it's taking hours, this is also something that isn't normal.
I'd look at local environmental issues like a firewall or IPS running on
your system.
If it is spiking while you are doing the port scanning, you should see
nmap in your process list at some point. You could try doing a scan with
the built-in port scanner(s) for Nessus. I'd also kick your max checks
to something much higher like 20 and see if your scan times are different.
Ron Gula
Tenable Network Security
Richard van den Berg wrote:
I'm running nessus 3.0.5 on Debian 4.0 with a 2.6.18 kernel. The
hardware is a Pentium 4M 2.2 GHz with 1GB of RAM. I'm using nessj on
another system to connect to this nessus scan engine.
max_checks and max_hosts are both set to 2. I've enabled all plugins
except DoS and safe_checks are off. I use nmap for port scanning, and
the results are loaded from a gnmap file.
Occasionally the scanning system becomes very unresponsive, system load
shoots up to around 10 and the CPU is at 0% idle. Today is especially
bad with the system spending hours with continuously 60% of CPU time
spent on "system" with peaks of 80%. If I "kill -STOP" the nessus
processes, the system goes back to 99% idle. Only 800MB of RAM is used,
and no swapping occurs.
This causes nessus to take hours to scan a single host with only a few
open ports. Tcpdump shows that the hosts are still being scanned, but at
a very slow rate.
What could be the reason that my system is spending so much time on
kernel processes? Is there any tuning I can do to prevent this from
happening?
Sincerely,
Richard van den Berg
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