I’m seeing this problem quite a bit, and I believe a quick update to the install docs could really help users in my situation. I followed the install docs at https://docs.librenms.org/Installation/Installation-Ubuntu-1804-Apache/ to the letter, and it resulted in the poller not running. The solution for me was easy - I ran the poller-wrapper.py line from the cron file mentioned under “Cron job” manually and found I was missing the mysql python module. A quick “apt install python-mysqldb” fixed the problem.
I think that newer users would really appreciate it if, in the install docs, “python-mysqldb” was included in the “required packages” section, or if a note was added in the “Cron job” section to run “apt install python-mysqldb”.
Thanks!