How to fix error Failed binding to authentication address * port 1812: Address already in use freeradius

I once ran FreeRADIUS in debug mode:

sudo radiusd -X

And I noticed the following error:

Failed binding to authentication address * port 1812: Address already in use freeradius
/usr/local/freeradius/etc/raddb/radiusd.conf[84]: Error binding to port for 0.0.0.0 port 1812

The error indicates that the address is already in use, so you need to stop the running FreeRADIUS process, look for it and see what’s running on the ports:

sudo ps ax | grep radius
sudo netstat -tulpn | grep :1812
sudo netstat -tulpn | grep :1813
sudo netstat -tulpn | grep :67

In my case, /usr/sbin/radiusd was already started, it can be terminated by PID:

sudo kill -9 PID

Or so:

sudo /etc/init.d/radiusd status
sudo /etc/init.d/radiusd stop
sudo /etc/init.d/freeradius stop