affaan-m/ECC · error · Error

tmux session already exists

Error message

tmux session already exists: ${plan.sessionName}

What it means

executePlan refuses to start when a tmux session with plan.sessionName already exists (checked via 'tmux has-session -t'). This prevents attaching duplicate panes/workers into an existing session or silently reusing stale state from a previous run.

Solutions

1. Kill the existing session: run 'tmux kill-session -t <sessionName>' and re-run the orchestrator.
2. Use a different sessionName in the plan if the old session must be preserved.
3. Attach to the existing session ('tmux attach -t <sessionName>') if it is actually the run you want.
4. Check for and clean up leftover sessions after crashed runs: 'tmux ls'.

Example fix

// before (fails)
node orchestrator.js --session my-session
// after
tmux kill-session -t my-session
node orchestrator.js --session my-session

const { status } = spawnSync('tmux', ['has-session', '-t', sessionName], { stdio: 'ignore' });
if (status === 0) {
  console.error(`session '${sessionName}' exists — kill it first: tmux kill-session -t ${sessionName}`);
  process.exit(1);
}

try {
  executePlan(plan);
} catch (err) {
  if (String(err.message).startsWith('tmux session already exists')) {
    spawnSync('tmux', ['kill-session', '-t', plan.sessionName], { stdio: 'inherit' });
    executePlan(plan); // retry once after cleanup
    return;
  }
  throw err;
}

When it happens

Trigger: Calling executePlan twice with the same sessionName; a previous run crashed after creating the tmux session but before cleanup; skipExistingSession/precheck flag disabled so the has-session check runs and returns status 0.

Common situations: Re-running the orchestrator after an aborted run without cleanup; two team members launching the same session name concurrently; session left over from an interactive tmux experiment with the same name.

Related errors

• buildOrchestrationPlan requires at least one worker
• Cannot delete active session
• Cannot merge active session
• Cannot rebase active session
• Canonical session snapshot requires

AI-assisted analysis of affaan-m/ECC@8321021c54 (2026-09-16). Data as JSON: /api/errors/988a709475ab759e. Report an issue: GitHub.

Appendix: source

Thrown at scripts/lib/tmux-worktree-orchestrator.js:506

  const rollbackCreatedResourcesImpl = runtime.rollbackCreatedResources || rollbackCreatedResources;
  const createdState = {
    workerPlans: [],
    sessionCreated: false,
    removeCoordinationDir: !fs.existsSync(plan.coordinationDir)
  };

  runCommandImpl('git', ['rev-parse', '--is-inside-work-tree'], { cwd: plan.repoRoot });
  runCommandImpl('tmux', ['-V']);

  if (plan.replaceExisting) {
    cleanupExistingImpl(plan);
  } else {
    const hasSession = spawnSyncImpl('tmux', ['has-session', '-t', plan.sessionName], {
      encoding: 'utf8',
      stdio: ['ignore', 'pipe', 'pipe']
    });
    if (hasSession.status === 0) {
      throw new Error(`tmux session already exists: ${plan.sessionName}`);
    }
  }

  try {
    materializePlanImpl(plan);

    for (const workerPlan of plan.workerPlans) {
      runCommandImpl('git', workerPlan.gitArgs, { cwd: plan.repoRoot });
      createdState.workerPlans.push(workerPlan);
      overlaySeedPathsImpl({
        repoRoot: plan.repoRoot,
        seedPaths: workerPlan.seedPaths,
        worktreePath: workerPlan.worktreePath
      });
    }

    runCommandImpl(
      'tmux',

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