Which ports does CARLA use, and what is holding them?

Paths. scripts/… below is relative to the directory holding this SKILL.md. Your working directory is the user's project, not that directory, so prefix them with its absolute path or the command is not found.

The failure this prevents: a bind error is read as a broken install. CARLA's components do not search for a free port when theirs is taken. The simulator exits, and the Traffic Manager retries the same port twenty times and then raises. Both messages describe the symptom, neither names the process at fault — and on a developer machine the culprit is usually another CARLA, an editor, or a tool that defaults to the same number.

Docs/ref_ports.md is the full reference. This skill answers the live question: what is in use right now.

Instructions

Progress:
- [ ] Step 1: bash scripts/check_env.sh     (only fails with no ss and no lsof)
- [ ] Step 2: check — the CARLA ports and who holds them
- [ ] Step 3: act — free the port, or move the service that wants it

Step 1 — prerequisites

bash scripts/check_env.sh

Step 2 — check

bash scripts/ports.sh check

Prints one row per CARLA port with its expected role and the process actually listening:

PORT    STATE      ROLE                                          LISTENER
2000    IN USE     CARLA RPC server (-carla-rpc-port)            UnrealEditor 48250
2001    IN USE     CARLA sensor streaming (RPC+1)                UnrealEditor 48250
2002    IN USE     CARLA multi-GPU secondary router (RPC+2)      UnrealEditor 48250
8000    free       Traffic Manager RPC                           -
6256    IN USE     Unreal MCP server (editor only)               UnrealEditor 48250
8010    free       NVIDIA Cosmos example server                  -
8767    free       Alpamayo 2 Super model service                -

Read the LISTENER column, not the ROLE column. ROLE is what CARLA expects on that port; LISTENER is what is really there. A mismatch between them is the bug, and check calls out the common one — an editor serving MCP on the Traffic Manager's 8000.

Other subcommands:

Non-default bases come from the environment, so a server on another port still reports correctly:

PORT=3654 TM_PORT=8050 bash scripts/ports.sh check

Step 3 — act

Pick by which side is easier to move.

Never free a port by killing a process you did not start. An editor on these ports usually holds someone's unsaved level. Report what holds it and let the user decide.

Gotchas

• The Traffic Manager lives in a client, not in the simulator. The first client to call get_trafficmanager(port) becomes its server; later clients on the same port attach to it. A free 8000 with vehicles already on autopilot means they are driven from another process.
• ports.sh only sees TCP. ROS 2 is DDS over UDP, and its ports come from the domain id (7400 + 250 × domain), not from a port argument. Separate two ROS 2 stacks with ROS_DOMAIN_ID, not with ports.
• A 0.0.0.0 bind is reachable from the network; 127.0.0.1 is not. The simulator binds all interfaces, the Unreal MCP server only localhost.
• Unreal's own ports are not CARLA's. 1981/1989 are UnrealTraceServer and 1985/8558 are Zen Server; they appear whenever the editor runs and are nothing to do with a CARLA bind error.