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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