- Use `systemctl is-active` to check if service is running
- Cleaner that `grep` on `systemctl status` output
- Return success means service is running/active
- Return failure means not running which could be due to
stopped/failed service or that service does not exist
- Use `command -v` instead of `which`
Ref: https://github.com/koalaman/shellcheck/wiki/SC2230
- Follow Google "Shell Style Guide": indent, use "readonly"
- Minor: Rephrase comment, avoid all caps
