thanx helping

the path was right,
I forgot to register on the web site and then receive my activation key to update nessus.
and then do
#nessus-fetch --register XXXX-XXXX-XXXX-XXXX-XXXX
-bash: nessus-fetch command not found
btw : to update nessus when using a proxy u need to create a proxy settings file :
~/.nessus-update-pluginscr
i'm just saying that for those that will need to do it ...