Dear All,

We are managing a set of servers running Debian plus VMware Server (free 
version). All of them are pretty busy since each of them run several 
VMware Virtual Servers.

I am trying to come up with a way (aka Best Practice) of having all 
these machines virus scanned on a regular basis.

What we have in place right now is a cronjob that updates the virus 
database every 3 hours by calling freshclam:

0 0-23/3 * * * /usr/local/bin/freshclam --quiet > /dev/null 2>&1

And another cronjob which every 12th and 24th of each month executes a 
fullscan. The fullscan is triggered by this command:

nice clamscan -r -i -l /var/log/clamavlogs/scan-results.log /

Basically, we identify VMware Virtual Disks (.vmdk files) as infected. I 
  saw this thread, and already decided not to scan VMware Virtual Disks:

http://lurker.clamav.net/thread/20041211.113120.eff2b90a.en.html#20041211.113120.eff2b90a

Then I figured that something like this for the full scan may make sense:

clamscan -r -i -l logfile.log /bin /dev /initrd.img /lost+found /sbin 
/usr /vmlinuz /boot /etc /initrd /lib /opt /root /srv /tmp /var

But I am not really sure this approach is the best in terms of 
performance. I have been reading around for a while and saw a few times 
people recommending the DAEMON mode versus the clamscan mode. I am 
confused about what the daemon does; it seems to me that the daemon is 
listening there and you will connect to it in order to specify which 
files to scan. That does not make a big difference to the clamscan 
command. I must be missing something here.

I think that it would be nice if we could come up with some best 
practices while having a general purpose server being automatically scanned.

Let me throw a few questions to break the ice:

1) Daemon Mode vs. Clamscan Mode.
[1.1] What is the difference between them?
[1.2] Which one performs better to scan a big number of files regularly?

2) Frequency
[2.1] How often shall clamav update the virus database?
[2.2] Is freshclam a good method or there is other better?
[2.3] How often should a whole system scan be executed?

3) Resource utilization
[3.1] Is it advisable to call clamscan using NICE to lower the impact on 
the system?
[3.2] Is it possible/advisable to limit the amount of RAM/CPU?

Thank you so much!
unai



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