How to record a computer with ubuntu


I have succes to record my computer with Audacity and Windows.
I try do it with Audacity and ubuntu 17.04 (fully updated) without success, I need your help !
I try it on three computers and I meet the same problem : I can select the microphone, but I can’t select the computer.
How to select the computer to record it ?

On Ubuntu you need to record the PulseAudio “monitor”. See here for details:

Greats thanks I have sucess now !
For ubuntu your link is perfect !

Else, after that sucess I sucess the same purpose with debian gnome and debian lxde, it is not the same ubuntu’s method ;