{
  "id": "linux-service-lifecycle",
  "title": "Start, Verify, and Stop a Service",
  "category": "Linux Administration",
  "isolation_type": "shared_namespace",
  "difficulty": "Easy",
  "type": "task",
  "weight": 4,
  "description": "## Start, Verify, and Stop a Service\n\nUnlike the previous exercise (inspecting a service you must never touch), this one is yours to fully control.\n\n**Your task:**\n\n1. Start a small HTTP service in the background, listening on port 8890: `python3 -m http.server 8890 --directory /srv/service-lab &`, and save its PID to `/srv/service-lab/service.pid`\n2. Confirm it's actually listening, and record the result to `/srv/service-lab/status-before.txt` (write exactly `listening`)\n3. Stop it using the PID you saved\n4. Confirm it's actually gone, and record the result to `/srv/service-lab/status-after.txt` (write exactly `stopped`)",
  "hints": [
    {
      "title": "Starting and recording the PID",
      "body": "`$!` after backgrounding a command holds its PID.",
      "command": "mkdir -p /srv/service-lab\npython3 -m http.server 8890 --directory /srv/service-lab >/srv/service-lab/service.log 2>&1 &\necho $! > /srv/service-lab/service.pid"
    },
    {
      "title": "Verifying and stopping",
      "body": "`ss -lnt | grep 8890` confirms it's listening. `kill $(cat .../service.pid)` stops it using the PID you recorded, not a hardcoded number.",
      "command": "ss -lnt | grep 8890 && echo listening > /srv/service-lab/status-before.txt\nkill $(cat /srv/service-lab/service.pid)\nsleep 1\nss -lnt | grep 8890 || echo stopped > /srv/service-lab/status-after.txt"
    }
  ],
  "setup_commands": [
    { "command": "mkdir -p /srv/service-lab" }
  ],
  "validation": {
    "commands": [
      { "description": "confirmed the service was actually listening before stopping it", "command": "cat /srv/service-lab/status-before.txt", "expected_output": "listening", "match": "exact" },
      { "description": "confirmed the service is actually stopped now", "command": "cat /srv/service-lab/status-after.txt", "expected_output": "stopped", "match": "exact" },
      { "description": "the process is genuinely no longer running", "command": "kill -0 $(cat /srv/service-lab/service.pid) 2>/dev/null && echo RUNNING || echo GONE", "expected_output": "GONE", "match": "exact" },
      { "description": "port 8890 is genuinely no longer bound", "command": "ss -lnt | grep -q 8890 && echo BOUND || echo FREE", "expected_output": "FREE", "match": "exact" }
    ]
  },
  "default_namespace": "default",
  "teardown_commands": [
    { "command": "[ -f /srv/service-lab/service.pid ] && kill $(cat /srv/service-lab/service.pid) 2>/dev/null; rm -rf /srv/service-lab" }
  ]
}