Arma 3 Server Troubleshooting Guide

This is the catch-all we point Arma 3 admins at when something's wrong. Organised by symptom, because you usually arrive here knowing what you're seeing, not why. Start at the section that matches what the server (or the player) is doing, and only dig deeper if the first fix doesn't land.

If you only read one paragraph: most "won't start" problems are a missing mod PBO or a typo in server.cfg; most "won't show up in the browser" problems are a mod the client doesn't have or filters hiding it; most "BattlEye: client not responding" kicks are client-side, not your server; and most desync problems are CPU-bound, not bandwidth-bound.

New to Arma 3 hosting? Start with the Getting Started Guide and the Server Configuration Guide. Everything below assumes the server is already provisioned on LOW.MS and you can reach the panel at control.low.ms.

1. Server won't start or crashes on boot

Hit Start and the process dies within seconds, or it never gets past the loading screen. Open Log Viewer in the control panel first – Arma 3 is fairly loud about why it bailed. The actual cause is almost always in the last 50 lines before the process exits.

The usual suspects, in order of frequency:

Syntax error in server.cfg – a missing semicolon, an unmatched quote, or a stray brace. Arma 3's config parser is unforgiving. Edit via Configuration Files in the panel so you can see the whole file, and look at the line number the log complains about.
Missing mod PBO. You've listed a mod in the launch parameters but the folder isn't actually on disk, or it's named differently than what's in -mod="...". Mod folder names are case-sensitive on anything non-Windows, but even on Windows a typo like @CBA_A3 vs @cba_a3 will bite you if a mod references the other. Open File Manager and compare what's on disk to what your commandline says.
Missing mission file. If class Missions in server.cfg points at template = "coop01.Altis" and that PBO isn't in mpmissions/, the server logs the error and quits. Either upload the mission or comment the mission rotation out to confirm that's the cause.
Stale lock files after a crash. If the last process exited uncleanly, occasionally a leftover file sticks around and blocks the next boot. A full restart from the panel (not just Start) clears it.

When the log mentions a specific addon by name but you "have it installed," double-check that the .pbo is actually inside the @Addon/addons/ folder and not nested one level deeper after an unzip.

2. Server starts but doesn't appear in the in-game Server Browser

On LOW.MS the firewall is pre-opened for the full Arma 3 port range, so "my ISP blocked it" isn't usually the cause. What you're looking at is almost always one of:

verifySignatures mismatch against the browser filter. If the client has "Verified" filtered on and your server has verifySignatures = 0, it won't show up for them. Conversely, if you left verifySignatures = 2 but didn't upload the right .bikey files, players who run the listed mods get filtered out of the list. Clear Arma 3's in-game browser filters and re-search.
Mod filter on the client. If the client has "All mods playable with current setup" ticked and they don't have every mod you advertise, your server disappears from their list. Tell them to toggle it off or subscribe to the missing mods.
Browser cache in-game. Hit the refresh button in the Arma 3 browser – it doesn't live-update, and a freshly restarted server takes a minute or two to propagate through Steam's master server.
Direct-connect still works. Give players your connect string from the panel service page (IP and port 2302) and use Direct Connect while you narrow the browser issue down. If direct works, it's purely a listing/filter problem.

One modern note: Bohemia dropped the requirement to set steamPort and steamQueryPort in server.cfg a long time ago. The server auto-assigns them as game port +1 and +2. If you've copy-pasted an old config that sets them manually, delete the lines – leaving them wrong is worse than not setting them at all.

3. Players can't connect: "Session lost", BattlEye kicks, Steam auth failure

Symptoms vary, cause usually doesn't. Work through them in order:

"Session Lost" mid-connect. Almost always the client had a mod-version mismatch, a signature check failed, or the server hit a brief hiccup during load-in. Ask the player to retry once; if it persists every time, move on to the signature section below.

"BattlEye: Client not responding" – this one bites everybody at least once. It's a client-side network hiccup between the player and the BattlEye master, not your server. The usual fix path for the player (not you):

Close Arma 3 and Steam completely.
Delete the BattlEye folder inside the Arma 3 install directory, and delete BEClient_x64.dll from %LOCALAPPDATA%\Arma 3\BattlEye\.
Steam → right-click Arma 3 → Properties → Installed Files → Verify integrity of game files. Steam reinstalls BattlEye and prompts once for the anti-cheat install on the next launch.
Power-cycle their router if it keeps happening. Flaky home routers do drop long-lived UDP flows.

If you see dozens of players hitting this simultaneously and the server just restarted, that's different – your node went through a BattlEye update and players need to reconnect once the new build catches up.

"Steam authentication failed" / "Steam ticket check failed". The player's Steam isn't properly authenticated. Have them restart Steam, then relaunch Arma 3. This one's usually just that.

"Signature check timed out" or "Files X are not signed by a key accepted by this server" – see section 5.

4. "You cannot play/edit this mission; it is dependent on downloadable content that has been deleted"

This is a client-side error, even though the server is what triggered it. The mission was built with a mod or DLC the player doesn't have.

The message usually names the offending class right at the end, e.g. a3_characters_f_exp (Apex), CUP_Weapons, or rhsusf_infantry. Match that back to its mod:

a3_*_exp = Apex DLC (paid).
a3_*_tank = Tanks DLC.
a3_*_orange = Laws of War DLC.
Anything starting with rhs, cup, ace, cba = a Workshop mod the player hasn't subscribed to.

Share the full mod list from your server config with players before session – ideally as a Steam Workshop collection so they can one-click subscribe. If you're running heavy milsim (RHS + ACE + CBA + TFAR) and somebody's confused, it's usually CBA that's missing; half the other mods depend on it.

5. Signature mismatch: `verifySignatures = 2` and `.bikey` handling

For hardened public servers you want verifySignatures = 2 in server.cfg. That's the strict V2 check: every loaded addon must be signed, and the server must hold the matching public key (.bikey) in its keys/ folder.

Where it goes wrong:

Missing .bikey for a mod in your list. Kick happens the instant a client joins. Open the mod folder, look for a keys/ or serverkeys/ subfolder, and copy the .bikey up to the server's root keys/ directory.
Duplicate or stale keys. Old versions of a mod ship a different .bikey than the current release. Players on the new version get kicked against your old key. Clear out obsolete keys whenever you update a mod.
Too many keys. The engine has a practical ceiling on how many keys it loads cleanly. Servers that accumulate a lot of keys across years of mod turnover can start having load issues. If your keys/ folder is huge, prune anything you're not actually loading.
Mods that ship partially-signed content. Some Workshop mods only sign a subset of their PBOs. Those will never pass V2. Drop to verifySignatures = 0 temporarily to confirm that's the cause, then either swap the mod out or raise it with the mod author.

Headless clients also live or die by signatures. They need to connect from an IP listed in headlessClients[] and localClient[] in server.cfg. On LOW.MS, if you're running an HC on the same node, 127.0.0.1 in both arrays is the right answer. If the HC sits and says "connecting" forever with no progress, 9 times out of 10 the IP isn't whitelisted and the server is silently refusing it.

6. Low FPS, desync, rubber-banding

The single biggest surprise for new Arma 3 admins: this game is CPU-bound on a small number of cores, not bandwidth-bound. A 12-core box doesn't help if the sim thread is pegging one core at 100%. LOW.MS's Arma 3 plans are built around high per-core clocks for exactly this reason.

Things that actually move the needle, in order:

Cut the AI count. In Antistasi, Liberation, and similar AI-heavy missions, 200+ simultaneous AI on the server will destroy framerate no matter what hardware you throw at it. Either cap the count in the mission or offload groups to a headless client.
Headless client offload. Moving AI simulation off the main server thread and onto an HC is the single biggest FPS win Arma 3 has. If you're running a mission that supports it (Antistasi does, plenty of milsim frameworks do), turn it on.
Tune basic.cfg if the server genuinely has bandwidth headroom. Defaults are MaxMsgSend = 128 and MaxSizeGuaranteed = 512. Increasing MaxMsgSend to 256–384 and MinBandwidth to a realistic value for your plan can help high-player-count sessions. Don't just paste a "100-slot optimised" config off the internet – if you push values past what the network can carry, you'll make desync worse, not better.
Reduce view distance in-mission. Server-side setViewDistance on a busy mission is a free win; most players won't notice 2000m vs 4000m visually, but the server notices it a lot.
Scheduled restart. Arma 3 servers leak memory over long uptimes – not dramatically, but enough that a 24-hour-old server feels worse than a fresh one. Set a daily restart in Scheduled Tasks.

7. Admin can't `#login`

You set passwordAdmin in server.cfg, typed #login yourpassword in chat, and nothing happens. Or worse, "Wrong password."

You didn't restart the server after editing the config. Arma 3 only reads server.cfg on process start. Stop and start from the panel after any config edit.
Whitespace in the password. A trailing space copy-pasted into passwordAdmin = "letmein " is a different password than letmein. Re-type it by hand.
Wrong command. In-game open the chat with /, then type #login yourpassword and press enter. Some mission frameworks rebind or swallow chat input – if nothing appears in chat at all, you've got a mission-side issue.
UID-based admin. If you've configured admins[] = { "76561198..." }; instead, typing #login with no password is the correct form. Give it no argument when your Steam UID is on the list.

8. RCON won't connect

Arma 3 RCON rides on the BattlEye protocol, configured via beserver_x64.cfg. On LOW.MS your RCON port is the one shown in the panel as TCP (typically the game port + 10, e.g. 2312) – not the default 2306 you'll find in random guides online. External tools need that port, not the default.

Checklist when a tool like BERCon, Arma 3 Server Tools, or BEC refuses to connect:

Confirm beserver_x64.cfg exists in the BattlEye folder and contains a line like RConPassword yourpassword and RConPort 2312 (using your actual allocated RCON port).
Confirm the tool is pointed at the server's public IP, not 127.0.0.1 – unless the tool is literally running on the game node, which it isn't for you.
Make sure the password matches exactly. BE RCON is picky about trailing whitespace too.
Restart the server after editing beserver_x64.cfg. Like server.cfg, it's only read on boot.
If you're running BEC as a watchdog, its own Config.cfg needs the matching password and port. It's a separate config from the BE one.

If you're still stuck, open Web Console and watch the server output as you connect – BE logs every failed RCON handshake with the reason.

9. Can't upload a mod / `.dll` upload blocked

SFTP on port 8822 (or FTP on 8821) both refuse .dll uploads by design – this is a platform-wide safety net, not an Arma 3 specific thing. For the vast majority of Arma 3 mods this is fine, because mods ship as folder-based .pbo files. Workshop mods like ACE, RHS, CBA, TFAR, Antistasi – all PBOs, no DLL in sight.

The exceptions are a small handful of engine-extension mods – Intercept Core is the one that comes up most often, plus the occasional dev tool. If a mod you need ships a .dll, don't try to rename it or work around the block. Open a ticket and we'll install it server-side for you, same day.

10. Scheduled restarts and running out of memory at high player counts

Arma 3 is a 64-bit engine and will happily eat every gig of RAM you give it if the mission keeps spawning entities. What starts as a smooth 40-slot server at Monday's restart will be crawling by Wednesday if nobody's rebooted it.

Two things to do:

Set up a daily restart in Scheduled Tasks. Once-every-24-hours at your community's quiet time is the sweet spot for most ops. For Antistasi and similar persistent campaigns, consider saving the mission state before the restart.
Watch RAM in Current Activity & Stats. If you're pinning against your plan's limit even right after a restart, you're on the wrong tier. The Arma 3 plans page lists RAM sizes and slot counts.

A 70-slot RHS + ACE + mission-heavy server genuinely needs more RAM than a vanilla 20-slot Altis Life box. Sizing down to save money and then hitting OOM at prime time is a false economy.

11. When all else fails

Log Viewer is always the first stop. The real error is usually there.
Web Console is the second – live output as things go wrong is often more useful than the log file after the fact.
Check the sidebar item titled "Server not starting? Please read!" in the panel if you see it; it covers edge cases we've hit on the platform.
The Bohemia community wiki on the Dedicated Server and server config parameters are both authoritative when something doesn't match this guide.
Still stuck? Open a ticket from control.low.ms. Paste the first 50 lines of log after the failure, tell us what you tried, and we'll dig in. Support's 24/7.