How to add custom mods to a Minecraft server?

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Prerequisites

• Access to your Oxygenserv panel (login and password).
• Server running a proper mod loader: Forge, NeoForge, Fabric, or Quilt (not plain vanilla).
• Mod .jar files from CurseForge/Modrinth that match your Minecraft version and loader.
• Required dependencies (e.g., Fabric API, Architectury, Cloth Config), if listed on the mod page.
• FTP/SFTP client (e.g., FileZilla) or the panel’s File Manager. Typical SFTP port: 22.
• Enough RAM available (e.g., 4–6 GB for a few mods, 8 GB+ for larger sets) and a fresh backup.

Step-by-step

1. Confirm mod compatibility
   On the mod page, note 1) the Minecraft version, 2) the loader (e.g., Forge vs Fabric), and 3) dependencies. Download the exact file for your server (e.g., 1.20.1 Forge). a) If the mod needs a library (like Fabric API), grab it too. b) Do not mix Forge mods with Fabric/Quilt. c) When in doubt, check the mod’s Files tab and description.
2. Install or switch to the correct mod loader
   Open your Oxygenserv panel, go to the “Version” or installer section, and select the loader that matches your mods (e.g., Forge 1.20.1, Fabric 1.20.4, NeoForge 1.20.1). Confirm and wait for the setup. If warned about a reinstall, create a backup first. After the first modded boot, a mods folder will be created automatically.
3. Stop the server safely
   Go to “Console” and click the red “Stop” button. Wait until you see the shutdown message. Never upload mods while the server is running—this risks data corruption. If the button seems stuck, refresh the page and ensure no auto-restart is scheduled.
4. Create a backup before changes
   In the panel, open “Backups” and click “Create backup”. Include at least world, mods, and config. You can also download these folders locally for extra safety. If you get a permission error, try again after a clean stop.
5. Upload mods to the mods folder
   Method A (panel): go to “Files”, open mods (create it if missing), then drag and drop your .jar files. Method B (SFTP): connect using your host, username, and password on port 22, then navigate to the server root and open mods. Upload every required .jar, including dependencies. If a file doesn’t show up, refresh and confirm the upload reached 100%.
6. Add dependencies and avoid loader mix-ups
   If a mod requires a dependency (e.g., Fabric API or Architectury), drop it into mods too. Don’t add Fabric mods on a Forge server (or vice versa) or you’ll see messages like “Missing Mod” or “Failed to apply mixin”. a) Keep a clear list of added files. b) Avoid duplicates (two versions of the same mod). c) If a mod is marked “client only”, don’t put it on the server.
7. Start and watch the logs
   Back in “Console”, click “Start” (or “Restart”). Monitor the startup—on success, you’ll see a ready/”Done” line. If it crashes, open logs/latest.log and check crash-reports/... to find the culprit. Common errors: “Missing mods” (dependency missing), “NoClassDefFoundError” (wrong version/loader), “Unsupported class file version” (Java too old).
8. Sync mods with your players
   On Forge/NeoForge/Fabric/Quilt, players must have the same mods and versions as the server (except strictly server-side mods). Share your list of .jar files or provide a modpack. Errors like “Incompatible modded server” or “Mismatched mod channel list” mean a mod/version mismatch on the client.
9. Test in-game and iterate
   Join the server and confirm new items/blocks work. If you notice lag after adding a mod, temporarily remove it to confirm the cause. When crashes happen, remove the last mod, reboot, then try a different build. Keep a backup of config/ if you tweak advanced settings.
10. Clean up and maintain
    To remove a mod: stop the server, delete its .jar from mods, and remove related files in config/ if needed. Restart and check logs. If chunks contained mod blocks, expect missing content—backups are your safety net. Schedule regular backups to stay safe.

Tips & optimization

– Java requirement: for Minecraft 1.18+ use at least Java 17 (1.20.5+ may target Java 21). Old Java triggers “Unsupported class file version”.
– RAM guidance: 4–6 GB for a few mods, 8–10 GB for medium packs, 12 GB+ for heavy modpacks. Don’t over-allocate without reason.
– Useful server-side performance mods: Forge/NeoForge → FerriteCore, Spark. Fabric/Quilt → Krypton, FerriteCore, Starlight.
– World settings: lower view-distance to 6–8 and simulation-distance to ~6 for steadier TPS on heavy setups.
– Add mods in small batches (3–5), boot, verify, then continue. This isolates conflicts fast.

FAQ

The mods folder is missing—what now?

Boot the server once with the loader installed (Forge/Fabric/Quilt/NeoForge) and it will create mods. If not, create a folder named exactly mods at the root, then reboot. If it still fails, you’re likely still on vanilla.

Do players need the exact same mods?

Yes for almost all Forge/NeoForge/Fabric/Quilt mods. “Server-side only” mods don’t require client installs, but anything adding blocks/items must match client and server. Compare .jar names and versions if you get mismatch errors.

Can I run mods and plugins together?

Not on pure Forge/Fabric. You need a hybrid server (e.g., Mohist, Magma, Arclight depending on versions) to support both. Note: stability varies and version coverage is limited. For maximum stability, avoid mixing if possible.

Server crashes on startup after adding a mod. How do I fix it?

Open logs/latest.log and crash-reports to find the mod named in the stacktrace. Remove it, verify loader (Forge vs Fabric), Minecraft version, and dependencies. Update to compatible builds and reboot. Add mods one by one to locate the culprit.

How do I move from vanilla to modded without losing data?

Make a full backup, install the loader (Forge/Fabric/Quilt/NeoForge) via the panel, boot once, stop, add your mods, and restart. Worlds are kept unless you wipe the disk. Keep a backup in case a mod requires a fresh world.

You’ve got this. Add mods in small steps, watch logs, and keep backups—your server will stay fast and stable. Need help? We’ve got your back.

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