Confirm a recorded PID is a Studio server before signalling it

unsloth_cli/commands/studio.py

@@ -2453,6 +2453,17 @@ def _pid_file_entries() -> "list[tuple[int, list[Path]]]":
     return list(by_pid.items())
 
 
+def _pid_is_studio_server(pid: int) -> bool:
+    """Guard against PID reuse: a stale record must not get an unrelated process
+    killed. Unknowable without psutil, so trust the record there."""
+    try:
+        import psutil
+        cmdline = " ".join(psutil.Process(pid).cmdline()).lower()
+    except Exception:
+        return True
+    return "run.py" in cmdline or "unsloth" in cmdline
+
+
 def _signal_stop(pid: int) -> "str | None":
     """SIGTERM (or taskkill) the pid. Returns an error string, or None on success."""
     import signal as _signal
@@ -2483,7 +2494,7 @@ def stop():
 
     signalled, failed = [], []
     for pid, paths in entries:
-        if not _pid_alive(pid):
+        if not _pid_alive(pid) or not _pid_is_studio_server(pid):
             for path in paths:
                 path.unlink(missing_ok = True)
             continue

unsloth_cli/tests/test_studio_stop.py

@@ -11,6 +11,7 @@ from __future__ import annotations
 
 import sys
 from pathlib import Path
+from types import SimpleNamespace
 
 import pytest
 from typer.testing import CliRunner
@@ -43,6 +44,7 @@ def _install(
     killed = killed if killed is not None else []
 
     monkeypatch.setattr(studio_mod, "_pid_alive", lambda pid: pid in live)
+    monkeypatch.setattr(studio_mod, "_pid_is_studio_server", lambda pid: True)
 
     def fake_kill(pid, _sig):
         killed.append(pid)
@@ -98,6 +100,7 @@ def test_stop_signals_each_server_once(monkeypatch, tmp_path):
     monkeypatch.setattr(studio_mod, "_PID_FILE", tmp_path / "studio.pid")
     monkeypatch.setattr(studio_mod.time, "sleep", lambda _s: None)
     monkeypatch.setattr(studio_mod, "_pid_alive", lambda pid: True)
+    monkeypatch.setattr(studio_mod, "_pid_is_studio_server", lambda pid: True)
     killed = []
     monkeypatch.setattr(studio_mod.os, "kill", lambda pid, _sig: killed.append(pid))
     monkeypatch.setattr(sys, "platform", "linux")
@@ -123,6 +126,46 @@ def test_stop_removes_every_stale_file_for_one_pid(monkeypatch, tmp_path):
     assert not list(tmp_path.glob("*.pid"))
 
 
+def test_stop_does_not_signal_a_reused_pid(monkeypatch, tmp_path):
+    # Crash leaves a per-port file behind, the OS hands that PID to something
+    # else: stop must drop the record, not SIGTERM an unrelated process.
+    studio_mod, _live, killed = _install(monkeypatch, tmp_path, alive = {8550})
+    monkeypatch.setattr(studio_mod, "_pid_is_studio_server", lambda pid: False)
+    _write_pid(tmp_path, "studio-8901-8550.pid", 8550)
+
+    result = _run_stop(studio_mod)
+
+    assert result.exit_code == 0, result.output
+    assert killed == []
+    assert not (tmp_path / "studio-8901-8550.pid").exists()
+
+
+def test_pid_identity_check_trusts_the_record_without_psutil(monkeypatch):
+    # No psutil: fall back to trusting the record rather than never stopping.
+    studio_mod = _studio()
+    monkeypatch.setitem(sys.modules, "psutil", None)
+
+    assert studio_mod._pid_is_studio_server(8550) is True
+
+
+def test_pid_identity_check_matches_a_studio_command_line(monkeypatch):
+    studio_mod = _studio()
+
+    class _FakeProcess:
+        def __init__(self, pid):
+            self.pid = pid
+
+        def cmdline(self):
+            if self.pid == 8550:
+                return ["/venv/bin/python", "/pkg/studio/backend/run.py", "--port", "8901"]
+            return ["/usr/bin/postgres", "-D", "/var/lib/pg"]
+
+    monkeypatch.setitem(sys.modules, "psutil", SimpleNamespace(Process = _FakeProcess))
+
+    assert studio_mod._pid_is_studio_server(8550) is True
+    assert studio_mod._pid_is_studio_server(9999) is False
+
+
 def test_stop_reads_the_legacy_single_pid_file(monkeypatch, tmp_path):
     studio_mod, _live, killed = _install(monkeypatch, tmp_path, alive = {4242})
     _write_pid(tmp_path, "studio.pid", 4242)
@@ -162,6 +205,7 @@ def test_stop_does_not_claim_a_stop_while_a_server_is_still_alive(monkeypatch, t
     monkeypatch.setattr(studio_mod, "_PID_FILE", tmp_path / "studio.pid")
     monkeypatch.setattr(studio_mod.time, "sleep", lambda _s: None)
     monkeypatch.setattr(studio_mod, "_pid_alive", lambda pid: True)
+    monkeypatch.setattr(studio_mod, "_pid_is_studio_server", lambda pid: True)
     monkeypatch.setattr(studio_mod.os, "kill", lambda pid, sig: None)
     monkeypatch.setattr(sys, "platform", "linux")
     _write_pid(tmp_path, "studio-8901-8550.pid", 8550)
@@ -181,6 +225,7 @@ def test_stop_continues_after_one_server_fails_to_stop(monkeypatch, tmp_path):
     monkeypatch.setattr(studio_mod.time, "sleep", lambda _s: None)
     live = {8550, 8600}
     monkeypatch.setattr(studio_mod, "_pid_alive", lambda pid: pid in live)
+    monkeypatch.setattr(studio_mod, "_pid_is_studio_server", lambda pid: True)
 
     def fake_kill(pid, _sig):
         if pid == 8550: