Fix high server load and memory/cpu consumption of clamd ( ClamAV )

I had troubles with one of Directadmin servers which was constantly loading because clamd process. When executing top command, clamd was always top on the list. As I researched, there is no way you can limit ClamAV’s memory and CPU consumption via its configuration itself. This is how you do it.

What you have to do is limit clamd within startup script, so that clamd will start with some limitations.

Just open ClamAV startup script. I this case CentOS 7:

vi /etc/systemd/system/clamd.service

Then add this lines. Of course change according to your needs.

IOSchedulingPriority = 7
CPUSchedulingPolicy = 5
MemoryLimit=256M
CPUQuota=30%
Nice = 19

Your startup script should now look something like this:

[Unit]
Description = Generic clamav scanner daemon
After = syslog.target nss-lookup.target network.target

[Service]
Type = simple
ExecStartPre=-/bin/mkdir -p /var/run/clamd
ExecStartPre=-/bin/chown -R clamav:clamav /var/run/clamd
ExecStart = /usr/local/sbin/clamd --foreground=yes
Restart = on-failure
PrivateTmp = true
IOSchedulingPriority = 7
CPUSchedulingPolicy = 5
MemoryLimit=256M
CPUQuota=30%
Nice = 19

[Install]
WantedBy = multi-user.target

malware acl condition: clamd: unable to send file body to socket (127.0.0.1)

If you see error like this in your mail logs, than chances are that your ClamAV is not able to process attachments files larger than limit set in clamav configuration. In this case, sender which sent email with larger attachment to your server, will get something like this in respond:

[10.10.10.10] #<[10.10.10.10] #5.0.0 smtp; 5.4.7 - Delivery expired (message too old) [Default] 451-'Temporary local problem - please try later' (delivery attempts: 75)> #SMTP#

In your mail log you’ll see something like this:

+++ 1e248B-000NMy-T6 has not completed +++
1969-08-15 01:40:21 1e248B-000NMy-T6 malware acl condition: clamd : unable to send file body to socket (127.0.0.1)
1969-08-25 01:40:21 1e248B-000NMy-T6 H=some.hostname.com [1.1.1.1] X=TLSv1:RC4-SHA:128 CV=no F=<prvs=449d2f142=senders@email.com> temporarily rejected after DATA

To solve this, open your clamav.conf file (/etc/clamav.conf or find your location) and change value for StreamMaxLength according to your needs. Default value is 25M.

Don’t forget to restart your ClamAV.

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