check_systemd_units: Ignore non-actionable scope failures

src/check_systemd_units.py

@@ -33,11 +33,17 @@
 import collections
 import datetime
 import logging
+import re
 import subprocess
 import sys
 import time
 import typing
 
+# Compiled regex for transient user/session units
+TRANSIENT_UNIT_RE = re.compile(
+    r'^(session-.*\.scope|user[@-].*\.(service|slice))$'
+)
+
 CheckResult = collections.namedtuple('CheckResult', ['code', 'msg'])
 
 logging.basicConfig(
@@ -61,7 +67,7 @@ def parse_args():
         action='append',
         default=[],
         help='Units to return critical when failed. Checking a timer unit'
-             ' will implicitly check the related service unit as well',
+        ' will implicitly check the related service unit as well',
     )
     parser.add_argument(
         '-i',
@@ -73,14 +79,14 @@ def parse_args():
     parser.add_argument(
         '-w',
         '--timer-warn',
-        default=3.,
+        default=3.0,
         type=float,
         help='Warning threshold of timer (inactivity/min_monotonic_interval)',
     )
     parser.add_argument(
         '-c',
         '--timer-crit',
-        default=7.,
+        default=7.0,
         type=float,
         help='Critical threshold of timer (inactivity/min_monotonic_interval)',
     )
@@ -118,8 +124,8 @@ def run_checks(args: argparse.Namespace) -> CheckResult:
     units = parse_units(raw_units)
     results = process(args, units)
 
-    logger.info('Criticals are: {}'.format(results[2]))
-    logger.info('Warnings are: {}'.format(results[1]))
+    logger.info(f'Criticals are: {results[2]}')
+    logger.info(f'Warnings are: {results[1]}')
 
     return gen_output(results)
 
@@ -147,9 +153,7 @@ def process(
         if res_code == Codes.OK:
             continue
 
-        logger.info('Problem for {} is: {} - {}'.format(
-            unit_id, res_code, res.msg,
-        ))
+        logger.info(f'Problem for {unit_id} is: {res_code} - {res.msg}')
         results[res_code].append((unit_id, res.msg))
 
     return results
@@ -175,7 +179,7 @@ def gen_output(
         else:
             problems[problem] = unit
 
-    logger.info('Problems are: {}'.format(problems))
+    logger.info(f'Problems are: {problems}')
     message += '; '.join([': '.join(i) for i in problems.items()])
 
     return exit_code, message
@@ -282,21 +286,30 @@ def check_unit(self, unit_id: str, timer: bool = False) -> CheckResult:
             )
         )
 
-        # Fast state checks first
+        # Ignore transient user/session units that are managed by logind.
+        # These come and go with user logins and are arguably harmless:
+        # * session-*.scope
+        # * user@.service
+        # * user-.slice
+        if TRANSIENT_UNIT_RE.match(unit_id):
+            logger.debug(f'Ignoring transient user/session unit {unit_id}')
+            return CheckResult(Codes.OK, '')
+
+        # Fast state checks
         if unit['LoadState'] != 'loaded' and unit['ActiveState'] != 'inactive':
             return CheckResult(
                 Codes.CRITICAL,
                 'the unit is not loaded but not inactive',
             )
-        elif unit['ActiveState'] == 'failed':
+        if unit['ActiveState'] == 'failed':
             return CheckResult(Codes.CRITICAL, 'the unit is failed')
-        elif unit['LoadState'] != 'loaded':
+        if unit['LoadState'] != 'loaded':
             return CheckResult(Codes.WARNING, 'the unit is not loaded')
 
         # Check the specifics about the different unit types
         if unit_id.endswith('.timer'):
             return self.check_timer(unit_id)
-        elif unit_id.endswith('.service'):
+        if unit_id.endswith('.service'):
             return self.check_service(unit_id, timer)
 
         return CheckResult(Codes.OK, '')
@@ -397,10 +410,11 @@ def check_intervals(self, unit_id: str) -> CheckResult:
         # We can check only monotonic triggers for regular execution
         checked_intervals = ['OnUnitActiveUSec', 'OnUnitInactiveUSec']
         intervals = [
-            (p[0], p[1]) for p in unit['TimersMonotonic']
+            (p[0], p[1])
+            for p in unit['TimersMonotonic']
             if p[0] in checked_intervals
         ]
-        logger.debug('Monotonic timers are: {}'.format(intervals))
+        logger.debug(f'Monotonic timers are: {intervals}')
         if not intervals:
             return CheckResult(Codes.OK, '')
 
@@ -462,7 +476,7 @@ def _check_interval(
             return CheckResult(
                 code,
                 f"the timer hasn't been launched since {last_trigger_human}, "
-                f"look at {service_unit['Id']}"
+                f'look at {service_unit["Id"]}',
             )
         return CheckResult(Codes.OK, '')