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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsServer-side mods in Arma 3 run on the dedicated server without being broadcast to every connected player. They are useful for administration, persistence, database or mission logic, and other functions that do not require a player’s game to load new models, sounds, maps, or client scripts. If a mod supplies anything the player must see or execute locally, that player still needs the mod installed and enabled.
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The reliable setup is to install the dedicated server, place each mod in a valid folder, launch it with the correct -mod= parameters, and enforce a deliberate signature-key policy. Workshop metadata can help the Arma 3 Launcher identify required client content, while careful version control prevents the PBO mismatches and signature errors that stop players from joining.
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What “server-side mod” means in Arma 3
Arma 3 distinguishes between content loaded by the server and content that must be loaded by each client. Bohemia Interactive’s dedicated-server documentation describes the -mod startup parameter as loading “server-side (not broadcasted to clients) mods.” In practical terms, the dedicated server reads the mod’s files and executes the portions that belong on the server; it does not automatically send that mod to players.
That description is about distribution, not a guarantee that every feature is invisible to clients. A mod can contain server logic and client-facing assets in the same release. The deciding question is whether a player’s game must load an asset or script to render the world, play audio, process an action, or participate in a feature.
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Content that can remain server-only
- Administration and moderation logic that runs on the dedicated server.
- Persistence, statistics, mission-state storage, and server-side databases.
- Rules, event scheduling, spawning logic, and other functions that do not add client assets.
- Automated server controls and management scripts that never need to execute in a player’s game.
Content that normally requires clients to install it
- New weapons, vehicles, uniforms, characters, maps, terrain objects, sounds, or visual effects.
- UI elements or interactive scripts that execute in the player’s game.
- Any mission dependency whose files are checked when a player joins.
When a release combines both kinds of content, follow its author’s installation instructions and test with a clean client profile. Calling a mixed mod “server-only” because its main purpose is administration can still produce missing-asset errors or a failed join.
Do players need to install a server-side mod?
Not if the mod is genuinely server-only and the mission does not require client files. Players can join with an otherwise unmodified Arma 3 installation when the server uses only server logic. They do need matching client content when the mod adds assets, client scripts, or a mission dependency that must be present locally.
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Use this decision test for every mod:
- Read the mod’s description and installation notes for a statement that it is server-only.
- List what the mod changes: administration and persistence usually stay server-side; assets and player UI usually do not.
- Run a join test with a client that has not subscribed to the mod.
- Check the server and client logs if the join fails. A missing required addon, a version mismatch, or a signature rejection means the content is not optional for that connection.
Do not assume that a successful connection proves every feature works. Test the specific commands, persistence operations, and mission events that the server-side mod provides.
Dedicated-server requirements and planning
Bohemia Interactive’s dedicated-server guide states that the dedicated-server package is free. It documents SteamCMD installation, Windows Server or a modern Linux distribution, and baseline hardware guidance. These figures are requirements and recommendations in the guide, not a performance guarantee for a particular mission, player count, AI load, or mod set.
| Resource | Minimum in the official guide | Recommended in the official guide | What affects the real requirement |
|---|---|---|---|
| Memory | 2 GB RAM | 4 GB RAM | Mission complexity, AI, extensions, logging, and the number of instances |
| CPU | 2.4 GHz dual-core | 3.5 GHz quad-core | Simulation load, server frame rate, AI count, and concurrent instances |
| Storage | 32 GB HDD | 32 GB SSD | Game files, Workshop downloads, logs, backups, and rollback copies |
Reserve additional disk space for multiple Workshop revisions and backups. A rollback is only useful if the previous mod files still exist. On a shared machine, isolate each instance’s configuration, profile, logs, port assignments, and key directory so an update for one server cannot silently alter another.
Install or update the dedicated server
SteamCMD deployment
SteamCMD is the practical choice for a repeatable dedicated server. Install SteamCMD on Windows Server or a supported modern Linux distribution, authenticate as required by Steam, and use it to install or update the Arma 3 dedicated-server app. Keep the installation directory under your control rather than mixing it with a desktop client’s game directory.
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After an update, record the build and preserve a copy of the startup script and configuration files. Updating the executable and updating Workshop mods are separate operations; perform them deliberately and restart the instance after either change.
Arma 3 Launcher for a small casual setup
For a small, manually managed server, the Arma 3 Launcher includes a Server option. This is convenient for a casual setup, but it offers less automation than a scripted SteamCMD deployment. It is still important to document the selected mods, ports, profile path, and launch parameters so the server can be rebuilt after a machine change.
Put mods in a recognized folder structure
Download required Workshop content on the server or copy the mod directories through a controlled deployment process. Do not drag individual PBO files into arbitrary folders. Keep each mod’s recognized root structure intact, including its addon PBO files and any supplied signature files.
A typical mod directory has a mod root containing an addons directory. The addon directory contains PBO files and, where the author supplies them, matching BISIGN signature files. Preserve capitalization and filenames when copying between Windows and Linux; a path that works on a case-insensitive filesystem can fail on a case-sensitive one.
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Launch server-side mods with the correct parameters
Start the executable, commonly named arma3server, with a -mod= parameter listing the server-side mod directories. Keep the list explicit and ordered, and quote paths that contain spaces according to the rules of the operating system and your service wrapper.
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Use -keysFolder= when you need key directories separated between instances. This is useful on a host running several servers with different trust policies. Ensure the account running the service can read the mod files and keys and can write the profile, logs, and BattlEye files.
Deployment checklist
- Stop the instance before replacing or updating a mod.
- Back up the current mod directory, startup script, configuration, and profile data.
- Copy the new mod directory without flattening its structure.
- Confirm the PBO files and supplied BISIGN files are present.
- Review the
-mod=list for spelling, separators, and duplicate paths. - Set
-keysFolder=if this instance uses an isolated key directory. - Start the server and inspect the startup log for missing directories, failed loads, or duplicate addons.
- Join with a test client before announcing the update to players.
For repeatable operations, store the launch command in a script or service definition and keep a dated change log. The exact command syntax around the executable, quoting, and service account depends on whether you run Windows or Linux, but the mod parameter and directory structure are the same concepts.
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Bohemia Interactive’s Workshop 101 instructs a player to subscribe to a mod, let Steam download it, open the Launcher’s MODS tab, select the mod, and press PLAY. That workflow is for client content, not a way to make server-only logic execute on a player’s machine.
The server browser can associate a server mod with its Workshop item. In the mod root, create a file named meta.cpp containing:
protocol = 1;
publishedid = 123456789;Replace the example number with the numeric identifier in the mod’s Workshop URL. With that metadata, the Launcher can identify the required Workshop item and help a player subscribe to and download missing client content. It does not turn a client-required mod into a server-only mod, and it does not remove the need for signatures or compatible versions.
Workshop pairing versus manual distribution
| Method | Advantages | Risks and work |
|---|---|---|
| Workshop pairing | Players can identify the item and download the intended release through Steam. | Workshop updates can arrive independently of your mission schedule; verify revisions before restarting a live server. |
| Manual distribution | You control the exact archive, revision, and rollback copy. | You must distribute files securely, communicate updates, and prevent clients from mixing old and new copies. |
Choose one source of truth for each mod. Mixing a Workshop copy, a manually copied archive, and an older local folder makes it difficult to prove which PBO a player is using.
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Signatures, keys, and trust policy
Arma 3 addon documentation describes PBO content, BISIGN signatures, and key creation with DSUtils. A signature allows the server to validate that an addon was signed by a key it trusts. The public key belongs on the server; the private signing key must remain with the party authorized to build or sign the addon.
Install only the public keys for mods you intentionally allow. A broad key folder weakens the purpose of signature checking because it tells the server to trust more signed content than you have reviewed. Keep a record of which key belongs to which mod and remove obsolete keys when you retire a mod.
How signature failures happen
- The server lacks the public key for an allowed, signed addon.
- The client has a different PBO revision from the server.
- A PBO or BISIGN file was copied incompletely or altered.
- The server is loading duplicate copies and validating a different file than expected.
- A mod was replaced without restarting the instance, leaving old files in memory.
When changing a signed mod, update the PBOs, matching signatures, and the corresponding public key as one controlled change. Restart the server and verify the startup log before testing a client connection.
BattlEye and automated server administration
BattlEye documents that server commands can be sent through RCon and that commands can be executed automatically from BEServer(_x64).cfg; on Linux the filename is written as beserver(_x64).cfg. Keep BattlEye configuration with the instance that uses it and restrict access to RCon credentials and ports.
Automated commands are separate from Arma mod loading. A server-side administration mod may provide its own commands or persistence, while BattlEye controls anti-cheat enforcement and remote administration. Test both layers after an update: confirm that the mod loads, then confirm that the BattlEye configuration still accepts the intended RCon or scheduled commands.
Windows versus Linux administration
| Consideration | Windows Server | Modern Linux distribution |
|---|---|---|
| Installation | SteamCMD and the dedicated-server files can be managed with Windows services or scheduled tasks. | SteamCMD can be managed with a service manager and shell scripts. |
| Paths and filenames | Case-insensitive behavior can hide capitalization mistakes. | Case-sensitive paths make exact mod and key names important. |
| Updates | Use a maintenance script or service stop/start sequence. | Use scripted backups, updates, permissions checks, and service restarts. |
| Administration effort | Familiar GUI tools may simplify casual management. | Automation and remote administration are strong, but permissions and service logs require care. |
Neither operating system removes the need for version control, backups, correct ports, or a tested launch command. Select the platform your administrator can patch, monitor, and recover confidently.
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Self-hosting or managed hosting?
Self-hosting gives direct control over files, startup parameters, update timing, keys, logs, and rollback copies. It also makes you responsible for SteamCMD maintenance, firewall and port configuration, storage, operating-system updates, backups, and every mod revision.
Managed hosting can reduce routine work by handling some combination of SteamCMD updates, port setup, storage, Workshop synchronization, and operating-system administration. Features differ by provider and change over time, so verify the current game version support, server locations, Workshop automation, operating-system model, backup options, access to startup parameters, and terms before committing. A host that hides the mod directory or prevents custom -mod= and key settings may be unsuitable for a server-side-mod workflow.
Fix PBO mismatch, signature, and join errors
PBO mismatch or “different data” error
Bohemia Interactive’s known-issues guidance says a PBO error means the server is using different data from the client. The documented recovery is:
- Note the exact PBO named in the error.
- Delete that PBO and its accompanying BISIGN file from the affected client mod directory.
- Verify the Arma 3 game files through Steam.
- If the file belongs to a Workshop mod, redownload the mod or unsubscribe and resubscribe so Steam obtains a clean copy.
- Restart the Launcher, enable the intended mod revision, and try again.
- If the error continues, contact the server administrator and provide the PBO name, mod revision, and server address.
On the server, compare the mod directory with the approved release and remove duplicate copies. Do not “fix” a mismatch by copying a random client PBO to the server; establish which revision the server is meant to run, then distribute that exact revision.
Signature or “missing key” error
- Confirm the server has the public key for every signed addon it intentionally allows.
- Check that the key belongs to the current mod release, not an older replacement.
- Make sure the client’s PBO and BISIGN files were downloaded as a matched set.
- Inspect the
-keysFolder=path and file permissions if the server uses a separate key directory. - Restart the instance after changing keys or signed files.
Version or required-mod join failure
Bohemia Interactive support warns that joining can fail when the game version differs or when the server requires user-generated addons and mods. Keep the dedicated-server build, mission, server mod list, Workshop revisions, and each client launch profile aligned. If only one player fails, have that player disable stale local copies and redownload the required Workshop items. If everyone fails after a server update, roll back the server and mod set together to the last known-good snapshot.
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- Confirm the mod appears in the startup log and is listed in the actual service command, not only in a desktop shortcut.
- Check that the mission invokes the mod’s required configuration or server-side component.
- Verify that the server account can read the mod and write the profile or persistence location.
- Test with one mod enabled at a time if several updates were deployed together.
- Review BattlEye and server logs for blocked commands, missing files, or script errors.
A safe update and rollback routine
- Announce a maintenance window and stop the server cleanly.
- Back up the executable version record, launch script, mission files, profile, keys, configuration, and current mod directories.
- Download the new Workshop revision or controlled archive without deleting the rollback copy.
- Compare the mod list and check whether the release adds client dependencies.
- Replace the mod atomically, preserving the recognized folder structure and signatures.
- Update the server’s
-mod=list or-keysFolder=path only when required. - Start the server, inspect logs, and connect with a test client.
- Exercise administration, persistence, mission start, and any mod-specific commands.
- Record the date, server build, mod revision, key changes, and test result.
If the test fails, stop the server and restore the complete previous snapshot rather than mixing old and new PBOs. A rollback is meaningful only when the executable, mission, configuration, keys, and mod files are restored as a compatible set.
Quick Recap
Practical decision guide
| Your situation | Recommended approach |
|---|---|
| You need administration or persistence only and players should join unmodified. | Use a genuinely server-only mod, load it with -mod=, and test a clean client. |
| The mod adds weapons, terrain, UI, sounds, or other assets. | Treat it as client-required; use Workshop pairing or a controlled manual distribution process. |
| You run several instances on one machine. | Separate profiles, ports, logs, mod paths, and key directories; use -keysFolder= where appropriate. |
| You need exact rollback control. | Keep dated archives and update manually or through a deployment script that preserves revisions. |
| You want less operating-system maintenance. | Evaluate managed hosting, but verify current Workshop, startup-parameter, storage, backup, and operating-system capabilities first. |
Key points to remember
-mod=loads server-side mods; it does not automatically install anything for players.- Players need a mod when its assets or scripts must run locally, even if the same package also contains server logic.
- Workshop
meta.cppmetadata helps the Launcher identify a required item; it is not a substitute for compatible files and signatures. - Public keys define which signed addons the server trusts, so install only keys for approved mods.
- PBO mismatches are data mismatches: identify the named file, obtain a clean matching revision, and keep the server and clients aligned.
- Backups, explicit launch parameters, isolated instance directories, and a tested rollback are more valuable than an improvised hotfix.
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