How do I upload an existing world?
The first thing you to need to do is find your Valheim server files, if you are using a cloud hosting provider (like ServerFlex) you'll need to use an FTP client like FileZilla to access your server files, if you're running the server locally then you'll need to find the Valheim server folder on your machine. (On Windows this is located at: "C:\Users\yourusername\AppData\LocalLow\IronGate\Valheim\worlds")
Now that you've found the files and folders for your Valheim server you need to find the "worlds" folder and double click on it. Inside this folder you should see at least two files, these files come in pairs so there should be a "world.fwl" file and a "world.db" file. Valheim splits the world data into two files so when uploading the new world you must include both of them.
Find your existing world files on your local machine, these files will be the name you chose when you created the world on your Valheim client. As mentioned previously you will need both the ".fwl" and the ".db" files for your world. Next you need to add these to the "worlds" folder in your Valheim server.
Now that we've added the files to your Valheim server we can configure the server to start with that world. Depending on how you host a Valheim server this part may be different so it's important to check with your Valheim hosting provider before proceeding. If you are hosting the server locally you will need to head back to the Valheim server base directory and find the file "start_server.sh" and open it in a text editor. It should contain something like this:
echo "Starting server PRESS CTRL-C to exit"
# Tip: Make a local copy of this script to avoid it being overwritten by steam.
# NOTE: Minimum password length is 5 characters & Password cant be in the server name.
# NOTE: You need to make sure the ports 2456-2458 is being forwarded to your server through your local router & firewall.
./valheim_server.x86_64 -name "My server" -port 2456 -world "Dedicated" -password "secret"
Note: If you're hosting with ServerFlex you can simply go to your server in our control panel and click on your world in your server settings.
Find the "-world" parameter near the bottom of the file and change the argument to the name of your world, don't forget to close the quote marks! Start your server again and you should now be able to play your existing world.
If you're a ServerFlex customer we've put together a video tutorial for how to simply upload your world through our control panel.
How do I create a new world on my Valheim server?
To create a new world you can simply change the command line argument to the name of a world that does not exist and restart the server. Unless you're using ServerFlex's control panel you won't be able to choose the seed for the server, so if this is important and you're not hosting a Valheim server with ServerFlex then you'll need to create the world locally and then add it to your server as an existing world.