Your first server

By the end of this page you will understand every choice Osmium asked you to make, and what each one wrote to disk.

Choose the server software#

Osmium installs three kinds of server software, and the kind decides whether the server takes mods or plugins. They are not interchangeable: a Fabric mod dropped into plugins/ is ignored, and a Paper plugin in mods/ is ignored just as quietly.

Osmium shows a one-line description beside each as you pick:

Start the wizard with no flags and it asks one question at a time:

$ osmium create

The steps are, in order: Choose Location, Name the Server, Choose Server Engine, Select Version, Allocate Memory, Agreements & Options, and Review. Anything you give as a flag is taken as answered and its step is skipped — which is what makes a fully specified osmium create run without a single prompt.

Choose a Minecraft version#

The version list is fetched live from Mojang's version manifest, so it is whatever is actually released. Osmium falls back to a short built-in list when it cannot reach the network.

Three different versions sit next to each other in this documentation and in the interface, so it is worth naming them apart:

• the Minecraft version — 1.21.1, the game version the server targets;
• the loader version or build — the Fabric loader version or the Paper build number, which Osmium handles for you;
• Osmium's own version — what osmium --version prints.

Allocate memory#

Memory is what the server is started with. 4G suits most small servers, and is the default until you change it in Settings or with --ram.

Accepted forms are gigabytes or megabytes — 6G, 10G, 3072M. Changing it later is osmium edit --ram 8G, and a running server keeps the old amount until it is restarted.

Accept the EULA#

A Minecraft server will not start until Mojang's EULA has been accepted. This is Mojang's requirement, not Osmium's; the server itself refuses to run otherwise.

The wizard's Agreements & Options step is where you accept it, and Osmium then writes eula.txt in the server folder. Passing --eula on the command line says you accept it and skips the step. The step is never skipped by anything else — an agreement cannot be accepted on somebody's behalf.

Add a mod or a plugin#

Which command you use follows from the server software. For a Fabric, Forge, NeoForge, Quilt or Vanilla server:

$ osmium mod add sodium -s survival

For a Paper, Purpur, Spigot or Bukkit server:

$ osmium plugin add luckperms -s survival

Both take Modrinth slugs. If you do not know the slug, search first — the search is narrowed to what fits this server's loader and Minecraft version:

$ osmium mod search world edit -s survival

To hold something at one particular build, name it: osmium mod add sodium@0.5.8. That is a pin, and updates leave it alone until it is unpinned.

Inspect the manifest#

$ cat osmium.json

{
 "category": "Mod Loader",
 "loader": "Fabric",
 "version": "1.21.1",
 "ram": "4G",
 "mods": {
  "sodium": "0.5.8",
  "spectrum": "*"
 },
 "plugins": {}
}

* means "whichever build is newest and compatible". A version number means that exact build and no other. There is nothing in between — Minecraft mods do not carry version numbers that a range could be written against, since an author may call a build 1.10.5-fabric, 0.102.0+1.21.1 or mc1.21.1-0.5.8.

Beside it, osmium.lock records what those requests resolved to, including everything pulled in as a dependency and which mod pulled it in. Both files are described in full in Configuration.

Start it, join it, stop it#

$ osmium start -s survival
$ osmium logs -s survival -f

The server binds to the port in server.properties, which is 25565 unless you change it. Osmium reads that file to know which port to talk about; it does not manage its contents beyond the gameplay settings exposed in the interface.

$ osmium details -s survival

While the server is running, details asks the server's own status port who is online, the way the game's server list does — nothing is typed into the console, so running it leaves no trace in the log.

$ osmium stop -s survival

Next#

Updating — three different things people mean by "update", kept apart.