Arma 3 server-side mods run on the dedicated server without being sent to connecting players. They are useful for administration, persistence, and rules that do not require new client-side assets. Players still need any mod that supplies models, textures, sounds, or scripts that must execute on their own computers. This guide explains how to install, launch, secure, update, and troubleshoot both server-only and mixed server/client mod setups.
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What “server-side mod” means in Arma 3
Arma 3’s dedicated-server startup parameter -mod loads “server-side (not broadcasted to clients) mods.” The server reads the mod’s files locally and does not distribute them through the game session. That makes a server-side mod different from a conventional content mod, where the client must also load the same addon before joining.
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The label describes distribution, not a special file type. A mod is server-only when all of its useful work can happen on the server. Administration tools, persistence databases, mission-management logic, anti-abuse controls, and some gameplay rules can fit that model. A mod stops being server-only when it depends on content or code that must run on a player’s machine.
When players do not need the mod
- The mod changes server administration or logging only.
- It stores or retrieves persistence data on the server.
- Its gameplay logic is evaluated entirely by the server and sends ordinary networked game state to clients.
- It does not add a model, texture, sound, animation, user interface, or client-executed script that the mission requires.
When players must install it too
- The addon supplies assets that must be rendered or played locally.
- The mission calls functions or scripts that are packaged in the addon and executed by the client.
- The mod changes a client interface or key bindings.
- The server or mission declares the addon as a required user-generated mod.
Some projects are mixed: one part can remain server-only while another component must be present on every client. Read the mod author’s dependency and installation notes rather than assuming that every item in a server’s -mod list is optional for players.
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Choose the right distribution model before installing
| Model | What is installed on the server | What players install | Main advantage | Main risk |
|---|---|---|---|---|
| Server-only | Logic, administration, persistence, or other non-client content | Nothing for that mod | Players can join with a standard client profile | A supposedly server-only feature may secretly depend on client code |
| Required client mod | The mod and its dependencies | The same mod versions and dependencies | Rich assets and client features are available | Version, signature, and missing-addon errors prevent joining |
| Optional client pairing | Server component | Optional Workshop item or companion component | Can provide extra features without blocking a basic client | Feature behavior differs between equipped and unequipped players |
Decide whether you want strict, reproducible content or a low-friction public server. A strict mod set is easier to test because every participant has the same files. A server-only design is easier for casual players because it reduces downloads and client launch errors.
Server requirements and hosting choices
Bohemia Interactive’s dedicated-server guide describes the package as free and supports installation with SteamCMD on Windows Server or a modern Linux distribution. Its baseline figures are guidance, not a performance guarantee.
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| Resource | Minimum guidance | Recommended guidance | Qualification |
|---|---|---|---|
| Memory | 2 GB RAM | 4 GB RAM | Official baseline; real needs rise with player count, missions, AI, and mods |
| CPU | 2.4 GHz dual-core | 3.5 GHz quad-core | Clock and architecture alone do not predict server FPS |
| Storage | 32 GB | 32 GB SSD | Leave additional room for Workshop downloads, logs, backups, and rollback copies |
Self-hosting
Self-hosting gives you direct control over the dedicated-server files, startup parameters, key directories, update timing, logs, firewall rules, and rollback archives. It also makes you responsible for SteamCMD maintenance, operating-system updates, port forwarding, bandwidth, storage, backups, and mod synchronization.
Managed hosting
A managed host can reduce the operational work around SteamCMD, network ports, storage, operating-system administration, and Workshop updates. The trade-off is less control over update timing, filesystem layout, startup flags, and emergency rollback. Before choosing a provider, verify its current game version support, geographic location, Workshop automation, operating-system policy, backup method, mod-size limits, and access to configuration files. These features and prices change, so treat them as contract terms rather than assumed capabilities.
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Install the dedicated server
SteamCMD workflow
- Install SteamCMD on the Windows Server machine or modern Linux distribution that will run the instance.
- Use SteamCMD to install or update the Arma 3 dedicated-server package into a dedicated directory.
- Create a separate data directory for the instance’s configuration, profiles, logs, missions, keys, and downloaded mods. Keeping it separate from SteamCMD makes backups and parallel instances safer.
- Open only the network ports required by your server configuration and apply the host’s firewall rules. Confirm that the process is reachable from another machine before adding mods.
- Launch the unmodded server once. This creates profile and configuration files and proves that the executable, permissions, ports, and BattlEye setup work independently of Workshop content.
Arma 3 Launcher option
For a small casual setup, the Arma 3 Launcher includes a Server option. It is convenient for a single operator who wants to select content graphically, but a scripted SteamCMD deployment is easier to reproduce, automate, and roll back on a long-running public server.
Download and place mods correctly
Use a controlled deployment process: download Workshop content on the server or copy a tested mod directory from a staging machine. Do not edit files inside a live mod while players are connected.
- Obtain the exact mod release and every stated dependency.
- Keep each mod in its recognized root folder, normally using an ordinary directory name or the Workshop-style name supplied by the author.
- Verify that the root contains the expected addon structure, including an
addonsdirectory with the mod’s PBO files. - Preserve any supplied signature files. A signed addon commonly has a corresponding
.bisignfile next to its PBO. - Place public key files in the server’s key directory. If multiple instances share a machine, use a separate key directory for each instance and point the launch command to it with
-keysFolder=. - Record the mod version, download date, dependencies, and checksum or archive name in a deployment note. That record lets you reproduce a working build after an automatic Workshop update.
Avoid mixing files from different releases. Copying a new PBO over an old directory while leaving obsolete files behind can create mismatches that are difficult to diagnose.
Launch server-side mods with startup parameters
Add server-only content to the executable’s -mod= parameter. Separate multiple mod directories with semicolons in the value used by your launcher or startup script. Use the exact directory names and quote the complete value when a path contains spaces.
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arma3server_x64.exe -port=2302 -profiles=C:Arma3profiles -mod=@ServerLogic;@Persistence -keysFolder=C:Arma3instance1keysThe executable name and path differ between installations; the important parts are the -mod= list and, when needed, -keysFolder=. Keep server-only mods in this list. For a client-required mod, document the same release for players and include any dependency in the correct load order.
Use a repeatable launch script
- Store the command in a batch file on Windows or a shell/service unit on Linux.
- Keep configuration, profiles, logs, keys, and mod directories in known locations.
- Write the selected mod set and game build to the log at startup.
- Restart only after a clean shutdown so profile and persistence files are flushed.
- Maintain a second, known-good launch profile with the last tested mod versions for rollback.
Pair a server with a Workshop item
Workshop pairing helps the Arma 3 Launcher identify content associated with a server. It is useful for mods that players must download; it does not magically turn client-required content into server-only content.
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Bohemia Interactive’s Workshop instructions tell a player to subscribe to a mod, let Steam download it, open the Launcher’s MODS tab, and press PLAY with the selected mods. A server can expose the corresponding Workshop item by placing a meta.cpp file in the mod’s root directory.
protocol = 1;
publishedid = 123456789;Replace the example number with the numeric published ID in the Workshop URL for that item. Keep the file in the mod root, not inside addons. After restarting the server, check the launcher or server browser to confirm that the item is associated with the expected folder.
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Workshop pairing versus manual distribution
| Approach | Best for | Control | Common failure |
|---|---|---|---|
| Workshop pairing | Public servers whose players can use Steam subscriptions | Easy discovery and download | A Workshop update changes files before the server has been tested |
| Manual archive or controlled copy | Private groups, staged releases, and strict rollback requirements | Exact version and timing | Players receive an outdated archive or incomplete dependency set |
Signatures, keys, and BattlEye
Arma 3 addon signatures allow a server to validate the files presented by a client. A signed PBO is accompanied by a BISIGN signature, and the server uses the mod’s public key to verify it. Signature creation and related key operations are documented with DSUtils.
Apply a deliberate key policy
- Obtain keys only from mods you intentionally permit.
- Copy the public
.bikeyfiles into the instance’s key directory, or into the directory selected by-keysFolder=. - Do not place private signing keys on the production server.
- Remove keys for retired or untrusted mods when you remove those mods from the allowed set.
- Restart the server after changing keys and test a permitted client and a deliberately unpermitted client.
Accepting every key defeats the purpose of signature checking. Conversely, enabling strict checking without installing the intended public key will reject legitimate clients.
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BattlEye supports server commands through RCon. Commands can also be executed automatically from BEServer.cfg (or beserver.cfg on Linux; the 64-bit filename is commonly BEServer_x64.cfg). Protect the RCon password, restrict remote access at the firewall, and keep the configuration readable only by the service account. Test administrative commands from an authorized console before relying on an automated rule.
Keep server and client versions aligned
Every required client mod must match the server’s tested release and dependencies. “Latest” is not a stable deployment policy: Workshop authors can publish a new revision while your mission, configuration, or companion mods still expect the previous one.
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- Freeze a known-good mod list for each public event or campaign.
- Update one mod at a time on a staging instance.
- Start the server without players and inspect the startup log for missing dependencies or duplicate addons.
- Join with a clean client profile that contains exactly the documented mod set.
- Run the mission, test persistence, reconnect, and check the server log before promoting the update.
- Keep the previous directories or archives until the new build has survived a complete play session.
For a server-only mod, clients should not be asked to subscribe merely because the server uses it. For a required mod, publish the exact Workshop item, revision policy, dependencies, and launch order to players.
Troubleshoot PBO mismatches and signature errors
“PBO mismatch” or a data-difference message
Bohemia Interactive describes a PBO error as the server and client using different data. The usual causes are a partial Workshop update, stale files left in a mod directory, a server updated before its clients, or two releases with the same folder name.
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- Stop the game and remove the named PBO and its accompanying BISIGN from the affected client or server mod directory.
- Verify the Arma 3 game files through Steam on the affected installation.
- Redownload or resubscribe to the Workshop mod, or recopy the controlled archive used by the server.
- Compare the server’s mod version and dependency list with the client’s launch profile.
- Restart the server and test with one clean client before inviting the rest of the group.
If the same mismatch continues after a clean verification and redownload, the server administrator should check for duplicate mod folders, stale PBOs in a second search path, or a Workshop revision that was not deployed consistently.
Signature or “missing key” error
- Confirm that the client has the signed PBO and matching BISIGN file.
- Confirm that the server has the corresponding public BIKEY, not a private key.
- Check that the key is in the active directory selected by
-keysFolder=. - Remove obsolete keys and restart so the running instance is using the intended policy.
- Do not solve a single bad key by accepting all keys; identify the exact mod that should be trusted.
Join failure caused by version or required content
Support documentation notes that joining can fail when the game version differs or when the server requires user-generated addons and mods. Check the Arma 3 build on both sides, then compare the server’s required-mod declaration with the client’s launch profile. A player who has subscribed to a Workshop item may still be running an old local revision, missing a dependency, or launching a different preset.
The server starts but a feature does not work
- Check the server log for a missing function, dependency, or failed initialization.
- Confirm that the mission actually calls the mod’s server-side component.
- Test with the mission’s documented parameter values and a fresh profile.
- Determine whether the feature is truly server-only; a user interface or local script may require a client companion mod.
- Disable unrelated mods on a staging copy and add them back one at a time.
Windows and Linux administration differences
| Task | Windows approach | Linux approach |
|---|---|---|
| Installation | Run SteamCMD and store the server in a dedicated directory | Install SteamCMD through the distribution’s supported method and use a service account |
| Startup | Batch file, shortcut, or service wrapper | Shell script or system service with explicit working and profile directories |
| Paths | Use quoted paths and backslashes where required | Use absolute paths, correct ownership, and forward slashes |
| Keys | Use the instance key directory or -keysFolder= |
Use the Linux BattlEye filename convention and restrict file permissions |
| Updates | Schedule SteamCMD and restart tasks through the host’s task tools | Schedule jobs or service restarts while preserving logs and exit status |
The mod-loading rules are the same; the important differences are path syntax, permissions, service supervision, and the BattlEye configuration filename convention.
A practical deployment checklist
- Classify every mod as server-only, required client, optional client, or dependency.
- Record the Arma 3 build, mod versions, Workshop IDs, and dependencies.
- Install the dedicated server and test an unmodded launch first.
- Copy complete mod directories, including PBO and BISIGN files.
- Install only the public keys for intentionally allowed signed mods.
- Use
-mod=for server-side directories and-keysFolder=when instances need separate key sets. - Add
meta.cppwithprotocol = 1;and the correct numericpublishedidwhen Workshop pairing is appropriate. - Test on a staging instance, then join with a clean client profile.
- Keep a tested rollback copy before accepting Workshop updates.
- Document the exact recovery action for each PBO, key, and version error.
Bottom line for choosing server-side mods
Use a server-only mod when its administration, persistence, or gameplay logic can execute entirely on the dedicated server. Use a synchronized client mod when the feature needs local assets, interfaces, or scripts. Install the server with SteamCMD or the Launcher’s Server option, load server-only directories with -mod=, keep signatures and public keys deliberate, pair Workshop content with a correctly written meta.cpp, and treat every update as a versioned deployment. Most join failures are solved by restoring identical game and mod data on both sides rather than by weakening signature or key checks.
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