ROOT canvas don't show


I have ROOT 6.20/04 and Ubuntu 20.04. I am trying to get familiar with ROOT but when I try to run simple examples like plotting something no canvas window shows up. If I type:
TF1 f1(“f1”,“sin(x)/x”,0.,10.);
then I just get:
Info in TCanvas::MakeDefCanvas: created default TCanvas with name c1
but nothing shows.

Can anyone help?

On your monitor, can you display any X11 graphical window originating from your Ubuntu (e.g. “xterm”)?