Most problems with an Arma 3 server come down to a few causes. Start with the one that matches what you see.
Players cannot find the server in the server browser
Why: The in-game list depends on Steam query traffic and can be slow to show a new server, and the browser filters hide servers with mods you have not loaded.
Fix: Use Direct connect on the Launcher's Servers page and enter the address and port from the Overview page. Clear the browser filters if you search by name.
Players are kicked on joining, or told their mods or signatures do not match
Why: The server checks mod signatures by default. Each mod needs its .bikey file in the keys folder, and players must load the same mods, with no unsigned or edited files.
Fix: Put the .bikey of every client mod in the keys folder, make sure players load the same mod set, and have them verify their mod files. Mods you uploaded yourself need their .bikey in the keys folder. A listed Workshop mod only gets its key if the server managed to download it, so check for its @ folder in Files.
A mod will not load, or the console reports missing files, after uploading it from Windows
Why: The Linux server is case sensitive and some mods fail when any file or folder name has capital letters.
Fix: Turn on Make Mod Files Lowercase, restart once, then you can turn it off again. Also make sure the folder name in Additional Mods is lowercase, has no spaces and does not start with a number.
The console warns that the modlist file could not be found or is invalid, and your preset mods are not loaded
Why: The file name in the Modlist File setting does not match the uploaded file, it is not in the server's main folder, or it was not exported from the Arma 3 Launcher.
Fix: Export the preset again from the Launcher's Mods page as HTML, upload it to the main folder, and enter exactly that file name in the Modlist File setting.
The mission stops and the server goes back to the lobby whenever everyone leaves
Why: Missions only keep running with no players when persistent is set to 1 in server.cfg, and it is 0 in the default server.cfg. Auto Initialize Mission is also skipped without it.
Fix: Set persistent = 1; in server.cfg and restart. If you want the mission to start by itself, also turn on Auto Initialize Mission.
#login does nothing or says the password is wrong
Why: passwordAdmin is still commented out or you edited it without restarting, or another admin is already logged in.
Fix: Remove the // before passwordAdmin in server.cfg (or add the line passwordAdmin = "yourpassword"; if it is missing), set your password, restart, then type #login with the same password. If someone else is admin, ask them to type #logout first.
You changed the player limit or password in server.cfg and it keeps reverting
Why: The server rewrites those two lines in server.cfg from the panel values every time it starts. The player limit is also fixed by your plan.
Fix: Change the password with the Server Password setting. The player limit follows your plan and cannot be raised in the file.
Server is slow, AI move in bursts, or players see heavy desync
Why: Arma 3 runs most of its work on one main thread, so large AI counts or heavy scripts overload it. Headless Clients only help with missions written for them.
Fix: Reduce AI counts or mission scripting, keep Server FPS at the default, and use Headless Clients only with a mission that supports them. Check the server's CPU and memory graphs in the panel.
Still stuck?
Open a ticket in the category that fits and include the last 50 to 100 lines of the console. See How to open a support ticket and How to fix a server that will not start.
