se a verificação de md5sum for suficiente para você, tente seguir o seguinte plugin:
nagios-exchange check_file_md5
Do manual:
Modeled after check_file_md5s, this script performs the following functions:
Permits arbitrary md5sum checking of a filename passed in on a parameter
Builds a list of files with every md5 check - warns when file isn't in the list and adds the file
Critical alert when a file is not present
Critical alert, followed by a refresh of the list of checksums when an md5 checksum doesn't match