Debian Stretch: No radutmp file though seeing Accounting message at network level

[Olivier]

Hello,

I'm currently testing SimultaneousUse setting in WPA2 Enterprise WiFi
environment.
I'm quite new to Radius (both concepts and implementations).

After reading this (very interesting) document [1], I assigned myself a
first step: seeing useful data through radwho command, no matter if
Freeradius relied on a completely different source on input to implement
SimultaneousUse feature.

In my testing, I'm having:
# radwho
Fri Sep 14 12:28:55 2018 : Error: Unable to check file
"/var/log/freeradius/radutmp": No such file or directory
radwho: Error reading /var/log/freeradius/radutmp: No such file or directory

1. I read in [2] then that /var/log/freeradius/radutmp is created by
Freeradius whenever it receives accounting data.
Is it correct on Debian Stretch when package's config is mostly  left
unchanged ?

2. At network level, I see that my WiFi AP are sending Account-Request and
receiving back Account-Response. Does it prove Freeradius's Accounting is
turned on and running or shall I for instance, read this Response content ?
Is there a better way to look at Freeradius "running features" ?

[1]
https://github.com/FreeRADIUS/freeradius-server/blob/v3.0.x/doc/configuration/simultaneous_use
[2]
http://lists.freeradius.org/pipermail/freeradius-users/2014-April/071808.html

Best regards