Merge ~vern/charm-hw-health:check_megacli_fix into charm-hw-health:master

[Vern Hart]

Properly handle return code of megacli cronjob Fixes LP: #1978896

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Paul Goins (vultaire)]

This is an unfortunate bug. It's one of the checks that we struggle to test since we don't have the target hardware, but this type of bug kind of begs for a unit test which mocks that out to a basic level.

The fix looks exactly like what we need. +1.

review: Approve

[Garrett Neugent (thogarre)]

Thanks for catching this Vern, and for fixing it proactively! +1 from me as well

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision a51a6cba0c3cca4c663e40030fe040e56fa005c6

diff --git a/src/files/megacli/check_megacli.py b/src/files/megacli/check_megacli.py
index be8c065..dc09607 100755
--- a/src/files/megacli/check_megacli.py
+++ b/src/files/megacli/check_megacli.py
@@ -61,9 +61,12 @@ def handle_results(nlines, match, critical, errors, num_ldrive, num_pdrive, poli
 def check_cron_return_code(rc_file=RC_FILE):
     with open(rc_file) as return_code_file:
         rc = return_code_file.read().strip()
-        if rc != 0:
+        try:
+            rc = int(rc)
+            if rc != 0: raise ValueError()
+        except ValueError as e:
             msg = "WARNING: megacli cron job failed, return code {}".format(rc)
-            raise WarnError(msg)
+            raise WarnError(msg) from None
 
 
 def parse_output(policy=False):  # noqa:C901