Fix srun detection causing permission error on non-SLURM platforms (#15485)

* improve srun detection
* changelog
* try catch is obsolete

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/lightning_lite/CHANGELOG.md

@@ -48,7 +48,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
--
+- Fix an issue with the SLURM `srun` detection causing permission errors ([#15485](https://github.com/Lightning-AI/lightning/issues/15485))
 
 -
 

src/lightning_lite/plugins/environments/slurm.py

@@ -15,8 +15,8 @@
 import logging
 import os
 import re
+import shutil
 import signal
-import subprocess
 import sys
 from typing import Optional
 
@@ -160,10 +160,8 @@ class SLURMEnvironment(ClusterEnvironment):
         """
         if _IS_WINDOWS:
             return
-        try:
-            srun_exists = subprocess.call(["command", "-v", "srun"]) == 0
-        except FileNotFoundError:
-            srun_exists = False
+
+        srun_exists = shutil.which("srun") is not None
         if srun_exists and not _is_srun_used():
             hint = " ".join(["srun", os.path.basename(sys.executable), *sys.argv])[:64]
             rank_zero_warn(

tests/tests_lite/plugins/environments/test_slurm.py

@@ -126,7 +126,7 @@ def test_srun_available_and_not_used(monkeypatch):
     expected = "`srun` .* available .* but is not used. HINT: .* srun python train.py --lr 0.01"
 
     # pretend `srun` is available
-    with mock.patch("lightning_lite.plugins.environments.slurm.subprocess.call", return_value=0):
+    with mock.patch("lightning_lite.plugins.environments.slurm.shutil.which", return_value="/usr/bin/srun"):
         with pytest.warns(PossibleUserWarning, match=expected):
             SLURMEnvironment()