I have been running a bitcoin app in an old server. I need to move everything to a new server but my question is this: is there a way I can transfer my bitcoin wallet (bitcoin core) to the new server with a clean O/S installation without losing the tx history from my old server's wallet?
Just shut down the bitcoin app on the old server, copy the
wallet.dat file to the new server, then start the bitcoin app on the new server. Don't remove anything from the old installation until you 100% confirm that the new installation works.