Can't detect the agent's user id, skipping some tests.

Hello.
I'm sorry to disturb but I tried several ways to fix it without any success...
When I'm executing the install.sh, I've this message and installation fails : 

id: 'npm': no such user
id: 'npm': no such user
Can't detect the agent's user id, skipping some tests.

I'm sure this is not complicated, but for me yes...
Thanks in advance for your help