Fix port 3080 already in use when starting DeepSeek Harness

Port 3080 already in use when starting DeepSeek Harness means a leftover or duplicate process holds the port and the new instance cannot bind — the browser is often still showing the old instance, which is why "the page opens but config changes never apply". Locate the owner (lsof -i :3080 / netstat -ano | findstr :3080), free the port or switch with dsh web --port 8080, then verify; prevent it with graceful shutdowns and process-list checks.

DeepSeek Harness port 3080 in use: old process holds the port, new instance cannot start

The classic symptom of port 3080 already in use: an old dsh process still holds 3080, the new instance cannot bind, and the browser keeps showing the old instance — everything looks normal except your config changes never take effect. It is a frequently reported runtime issue on the dshbase troubleshooting page (source):

1. You start dsh web and the terminal reports port 3080 in use (or silently switches ports and prints a new one);
2. The browser opens http://127.0.0.1:3080 and the page loads fine — because it is the old instance;
3. You change a config and restart, but nothing changes — the new instance never came up;
4. Key judgment: a loading page ≠ a healthy service; first confirm you are connected to the freshly started instance.

Why DeepSeek Harness reports port conflicts: leftover processes, duplicate instances, firewall interference

Port 3080 conflicts come from three sources: leftover processes (not fully exited), duplicate instances (multiple starts), and firewall or proxy interference (an occupancy illusion). In detail:

1. Leftover processes: closing the terminal window or force-killing dsh can leave child processes behind that still hold 3080 (source).
2. Duplicate instances: running the desktop app and dsh web against the same profile at once, or starting several web instances, leaves the later ones unable to bind.
3. Firewall / proxy interference: system firewall rules or a global proxy may intercept or forward 3080 traffic, showing up as "port in use with no process" — lsof finds nothing and you should check proxy rules instead.
4. dsh web listens on 127.0.0.1:3080 by default (confirmed in the official README, source); when the port is occupied, cases 1 and 2 are the usual cause.

Fix DeepSeek Harness port conflicts: locate the process, free or switch ports, verify

Follow the locate-then-act order: find the owner with lsof/netstat, kill it or switch ports, then open the browser to confirm the new instance. Step by step:

1. Find the process holding 3080: macOS / Linux:

   bash

   lsof -i :3080
   

   (On Linux you can also inspect the listener with ss -tlnp | grep :3080) Windows (PowerShell):

   powershell

   netstat -ano | findstr :3080
   

   Note the PID (the PID column of lsof / the last column of netstat). If the owner is not a system service, continue; if no process shows up yet the port is still blocked, skip to step 4 and check the proxy/firewall.

2. Free the port (kill the owner): macOS / Linux:

   bash

   kill -9 <PID>
   

   Windows:

   powershell

   taskkill /PID <PID> /F
   

   Run lsof -i :3080 (or netstat) again — no output means the port is free.

3. Switch ports (alternative when you do not want to kill anything) — --port belongs to the web app and must come after dsh web:

   bash

   dsh web --port 8080
   

   When the terminal prints http://127.0.0.1:8080, open http://127.0.0.1:8080 (source).

4. Check the firewall / proxy: when lsof finds no process but the port still will not open, check whether a global proxy forwards 127.0.0.1 traffic too — add the local address to the direct/bypass list, or temporarily disable the proxy and retry.

5. Verify: open http://127.0.0.1:3080 (or the new port) and confirm it is the freshly started instance; config changes should now apply immediately.

How to verify a DeepSeek Harness port change and restore the default port

After switching ports, verify two things: the new port is really listening and the page loads; to restore 3080, kill the old owner and run dsh web again. In order:

1. Confirm the new port is listening:

   bash

   lsof -i :8080
   

   A dsh process in LISTEN state means success; no output means the service did not start — recheck the fix section.

2. Verify in the browser: open http://127.0.0.1:8080; a page that loads and applies config changes immediately means the whole chain works.

3. Restore the default 3080: first kill the old process holding 3080 (macOS/Linux kill -9 <PID>, Windows taskkill /PID <PID> /F), then run:

   bash

   dsh web
   

   The terminal printing dsh web: http://127.0.0.1:3080 means the default port is back.

4. Free the port in one shot on Linux (optional): once you confirm the owner is dsh, use fuser to release it directly:

   bash

   fuser -k 3080/tcp
   

   Then lsof -i :3080 again — no output means the port is free.

Notes: DeepSeek Harness port conflicts — locate before killing

1. Close dsh with Ctrl+C for a graceful shutdown — the first Ctrl+C lets plugins clean up; press again to force exit if it hangs. Closing the window directly leaves the most leftovers.
2. Before starting, list processes: ps aux | grep dsh on macOS/Linux, tasklist | findstr dsh on Windows — handle old instances first.
3. Do not run the desktop app and dsh web against the same profile simultaneously; concurrent writes also cause session problems.
4. Plugin load failures can also break the Web UI — for plugin-related faults, check install history and errors in the DSH Plugin Hub at Settings → Plugin Market instead of guessing.
5. See install error troubleshooting for other DeepSeek Harness install issues.

Sources: dshbase troubleshooting, DeepSeek Harness CLI behavior reference, DeepSeek Harness README