Short answer:
You don't have to run it manually because it has been run automatically and is running in the background, that's why you receive that message.
If you want to stop the daemon and run it manually:
sudo systemctl stop clamav-freshclam.service
run it manually:
sudo freshclam
What is happening and how to handle it?
Every time when you encounter into a similar situations, errors like file x has been locked or Another process is using this file : /path/to/x you can use the lsof command to find out which process is using that file, in your case if you run:
sudo lsof /var/log/clamav/freshclam.log
You should get an output like:
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
abc 126 user 3wW REG 259,1 100 1048 /var/log/clamav/freshclam.log
The abc is the name of process which is using that file, in your case it's: freshclam.
That means freshclam which you want to run has been already ran by clamav daemons.
you can use less /var/log/clamav/freshclam.log or similar commands to see what's going on.
So you don't have to run it manually anymore, it's a process to avoid any conflict and having multiple instance of a same process doing same thing at the same time.
If you want to make it stop and run it manually, then send a SIGTERM to its process, that gives the process a chance to finish its job and close itself cleanly, something like:
sudo pkill -15 -x freshclam
- in this case
sudo may be necessary.
- 15: SIGTERM is the default
Then run it manually:
sudo freshclam
However in this case you can use:
sudo systemctl stop clamav-freshclam.service
to stop the daemon.