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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Stdio transport: MCP server process survives parent death (stdin EOF not causing shutdown)","articleBody":"### Initial Checks\n\n- [x] I confirm that I'm using the latest version of MCP Python SDK\n- [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue\n\n### Description\n\n## Stdio transport: MCP server process survives parent death (stdin EOF not causing shutdown)\n\n### Description\n\nWhen an MCP server using `transport=\"stdio\"` has its parent process die (e.g. the MCP client exits, is killed, or crashes), the server process is orphaned and continues running indefinitely. It gets reparented to init/systemd and never exits.\n\n### Expected behavior\n\nWhen the parent process dies and stdin reaches EOF, the server should detect this and shut down cleanly.\n\n### Analysis\n\nLooking at the code flow in `mcp/server/stdio.py`:\n\n1. `stdin_reader()` (line 60) iterates `async for line in stdin` where `stdin` is `anyio.wrap_file(TextIOWrapper(sys.stdin.buffer, encoding=\"utf-8\"))`\n2. When stdin reaches EOF, the loop should end, closing `read_stream_writer`\n3. This should close the `read_stream`, causing `server.run()`'s `async for message in session.incoming_messages` loop to end\n4. `run()` returns → `stdio_server()` context exits → task group cancels `stdout_writer` → process exits\n\nIn practice, the process survives. The likely cause is that `anyio.wrap_file` runs the underlying `readline()` in a worker thread, and this thread may not wake up or propagate EOF correctly when the pipe is closed due to parent death.\n\n### Reproduction\n\n```python\nfrom mcp.server.fastmcp import FastMCP\n\nmcp = FastMCP(\"test\")\n\n@mcp.tool()\nasync def hello() -\u003e str:\n    return \"hello\"\n\nmcp.run(transport=\"stdio\")\n```\n\n1. Start the server as a subprocess from any parent process\n2. Kill the parent process (e.g. `kill -9 \u003cparent_pid\u003e`)\n3. Observe that the MCP server process is still running (`ps aux | grep python`)\n4. The process is now reparented to init/systemd and will never exit\n\n### Environment\n\n- `mcp` version: 1.26.0\n- Python: 3.14\n- OS: Linux (Fedora 43)\n\n### Fix\n\nA proposed fix would be to monitor `stdin` via a selectors and when it becomes ready and returns \"\" shutdown the process.\n\n### Example Code\n\n```Python\nfrom mcp.server.fastmcp import FastMCP\n\nmcp = FastMCP(\"test\")\n\n@mcp.tool()\nasync def hello() -\u003e str:\n    return \"hello\"\n\nmcp.run(transport=\"stdio\")\n```\n\n### Python \u0026 MCP Python SDK\n\n```Text\nEnvironment\n\n    mcp version: 1.26.0\n    Python: 3.14\n    OS: Linux (Fedora 43)\n```","author":{"url":"https://github.com/arcivanov","@type":"Person","name":"arcivanov"},"datePublished":"2026-03-06T11:53:35.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/2231/python-sdk/issues/2231"}