Detail errors:
Jun 03 14:46:43 free freeradius[23499]: FreeRADIUS Version 3.0.20
Jun 03 14:46:43 free freeradius[23499]: Copyright (C) 1999-2019 The FreeRADIUS server project and contributors
Jun 03 14:46:43 free freeradius[23499]: There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
Jun 03 14:46:43 free freeradius[23499]: PARTICULAR PURPOSE
Jun 03 14:46:43 free freeradius[23499]: You may redistribute copies of FreeRADIUS under the terms of the
Jun 03 14:46:43 free freeradius[23499]: GNU General Public License
Jun 03 14:46:43 free freeradius[23499]: For more information about these matters, see the file named COPYRIGHT
Jun 03 14:46:43 free freeradius[23499]: Starting - reading configuration files ...
Jun 03 14:46:43 free freeradius[23499]: Debugger not attached
Jun 03 14:46:43 free freeradius[23499]: Creating attribute Unix-Group
Jun 03 14:46:43 free freeradius[23499]: /etc/freeradius/3.0/mods-enabled/rest[1]: Failed to link to module 'rlm_rest': /usr/lib/freeradius/rlm_rest.so: cannot open shared object file: No such file or directory
Jun 03 14:46:43 free systemd[1]: freeradius.service: Control process exited, code=exited, status=1/FAILURE
Error is Failed to link to module ‘rlm_rest’: /usr/lib/freeradius/rlm_rest.so: cannot open shared object file: No such file or directory
Fixing:
$ sudo apt install freeradius-rest
Run command again
$ sudo systemctl start freeradius
Reff: