Align monitoring exit codes and about error handling

[c-kr]

Return Codes And CLI Validation

Summary

This patch aligns top-level CLI handling and parser exits with the Monitoring Plugins guidelines:

• --help and "no command supplied" now return UNKNOWN (3) instead of OK (0).
• argparse usage and invalid command-line arguments now return UNKNOWN (3).
• ConnectionRefusedError now reports CRITICAL in both text and exit code.
• about no longer maps unexpected plugin-internal exceptions to CRITICAL; normal check results stay unchanged, but unexpected internal failures now surface as UNKNOWN.

Reference:

• https://www.monitoring-plugins.org/doc/guidelines.html

The relevant guideline points are:

• invalid command line arguments should return UNKNOWN (3)
• --help / --version should return UNKNOWN (3)
• plugin-internal failures should not be reported as CRITICAL

Files

• checkvsphere/tools/cli.py
• checkvsphere/cli.py
• checkvsphere/vcmd/about.py

Quick Verification

export PYTHONPATH="$PWD"
export VC_HOST='vcenter.example.com'
export VC_USER='monitor@vsphere.local'
export VC_PASS='secret'

1. No command supplied

python -m checkvsphere.cli
echo $?

Expected before fix:

• rc=0

Expected after fix:

• rc=3

2. Subcommand help

python -m checkvsphere.cli host-runtime --help
echo $?

Expected before fix:

• rc=0

Expected after fix:

• rc=3

3. Connection refused text/code mismatch

python -m checkvsphere.cli datastores -s 127.0.0.1 -o 1 -u x -p x
echo $?

Expected before fix:

• rc=2
• output starts with UNKNOWN - Connection refused

Expected after fix:

• rc=2
• output starts with CRITICAL - Connection refused

4. about internal error classification

This check needs a reachable vCenter. Point --sessionfile to a directory so writing the session ID fails after login:

python -m checkvsphere.cli about -s "$VC_HOST" -u "$VC_USER" -p "$VC_PASS" --sessionfile /
echo $?

Expected before fix:

• rc=2
• generic runtime failures inside about are reported as CRITICAL

Expected after fix:

• rc=3
• the failure is reported as UNKNOWN

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Assisted-by: Codex gpt-5.4 high