This check will monitor mysql open_files value raported to setted open_files_limit value. The plugin must be copied into /usr/lib/check_mk_agent/plugins folder and the executable bit must be set for this file.
The check will return current open_files_limit and open_files values. The check gets critical at 90 percent of open_files_limit and warning at 80.
Both limits are definable in Wato under "Parameters for Inventorized Checks", "Applications, Processes & Services".