[closed] Merging pbf quesion

I am trying to serve my own tiles and using the https://download.geofabrik.de/ pbf files, how can I concatenate or merge them to get a single world pbf?

I tried osmium to cat or merge and that did not work for me when I tried to create a docker image from the instructions on https://switch2osm.org/serving-tiles/using-a-docker-container/

Any advice appreciated!