I searched this issue in other topics but only found outdated topics with previous versions of Ubuntu. I'm using Ubuntu 18.04 in my laptop and I'm following the tutorial available at https://switch2osm.org/manually-building-a-tile-server-18-04-lts/ and was going fine, except for the last step, which is the tile viewing.
I'm opening the "sample_leaflet.html" file inside folder /src/mod_tile/extra/ using Firefox Browser and it doesn't show tiles. It only shows tiles at lv 0 zoom, which is the same tile shown at http://localhost/hot/0/0/0.png repeated side by side.
My console show the rendering messages, as the tutorial said it would do.