YAML is very sensitive to formatting. The way you published your configuration file gives us no clue about the formatting. See Formatting code and log snippets in posts and re-post.
You are not supposed to run mongod as root.
The message error command line: unrecognized line in ‘systemLog:’ does not look like an error message from mongod. Because it usually indicate the line number when yaml is wrong. May be you are using an old mongod and the error messages have been rewritten.