gh-138216: Fix testGetServBy fails on systems without certain entries in /etc/services

Lib/test/test_socket.py

@@ -201,6 +201,36 @@ def _have_socket_hyperv():
         s.close()
     return True
 
+def _query_available_service(expected_protocols, services_file = '/etc/services'):
+    if not os.path.exists(services_file):
+        return None
+    services_found = dict()
+    with open(services_file, 'r') as f:
+        for line in f:
+            line = line.strip()
+            if line.startswith('#'):
+                # Skip comment line.
+                continue
+            tokens = line.split()
+            if len(tokens) < 2:
+                continue
+            if '/' not in tokens[1]:
+                continue
+            try:
+                _, entry_protocol = tokens[1].split('/')
+            except:
+                continue
+            entry_name = tokens[0]
+            if entry_name not in services_found:
+                services_found[entry_name] = [entry_protocol]
+            else:
+                services_found[entry_name].append(entry_protocol)
+            for protocol in expected_protocols:
+                if protocol not in services_found[entry_name]:
+                    break
+            else:
+                return entry_name
+    return None
 
 @contextlib.contextmanager
 def socket_setdefaulttimeout(timeout):
@@ -1276,7 +1306,10 @@ def testGetServBy(self):
             except OSError:
                 pass
         else:
-            raise OSError
+            service = _query_available_service(('tcp'))
+            if service is None:
+                self.skipTest('No available service found.')
+            port = socket.getservbyname(service, 'tcp')
         # Try same call with optional protocol omitted
         # Issue gh-71123: this fails on Android before API level 23.
         if not (support.is_android and platform.android_ver().api_level < 23):

Misc/NEWS.d/next/Tests/2025-08-28-09-21-18.gh-issue-138216.lNF79V.rst

@@ -0,0 +1 @@
+Fix ``testGetServBy`` in ``test_socket.py`` on systems without certain entries in ``/etc/services``.