freeradius3 couldnt connect to mysql-server

[Lukas Nuth]

Hi,
FreeRADIUS starts with my virtual machine. Therefore Ubuntu created the 
file "radiusd.service" itself. I activated "radius.service" with 
"systemctl enable radiusd.service" so that FR starts with the virtual 
machine.
Now the problem when FR starts with the virtual machine is that the 
following error message can be found in the log file:

Mon Oct 22 08:45:40 2018 : Info: Debugger not attached
Mon Oct 22 08:45:41 2018 : Info: rlm_sql (sql): Driver rlm_sql_mysql 
(module rlm_sql_mysql) loaded and linked
Mon Oct 22 08:45:42 2018 : Info: rlm_sql_mysql: libmysql version: 5.7.23
Mon Oct 22 08:45:42 2018 : Info: rlm_sql (sql): Attempting to connect to 
database "radius"
Mon Oct 22 08:45:42 2018 : Info: rlm_sql (sql): Opening additional 
connection (0), 1 of 32 pending slots used
Mon Oct 22 08:45:42 2018 : Error: rlm_sql_mysql: Couldn't connect to 
MySQL server radius at localhost:radius
Mon Oct 22 08:45:42 2018 : Error: rlm_sql_mysql: MySQL error: Can't 
connect to local MySQL server through socket 
'/var/run/mysqld/mysqld.sock' (2)
Mon Oct 22 08:45:42 2018 : Error: rlm_sql (sql): Opening connection 
failed (0)
Mon Oct 22 08:45:42 2018 : Error: /etc/raddb/mods-enabled/sql[20]: 
Instantiation failed for module "sql"

If I restart FR with "systemctl restart radiusd.service" this error does 
not occur.

Can anyone help me?

regards
Lukas