The file system check utility FSCK is used to check and display the state of the file system, files and blocks in it. When used with a path (bin/Hadoop fsck / -files -blocks -locations -racks), it recursively displays the state of all files under the path. When used with '/', the entire file system is checked. By default, FSCK ignores files that are still open for writing by a client. To list such files, run FSCK with the -openforwrite option.  FSCK scans the file system, prints a dot for each file that is found to be healthy, and prints a message about the files that are not quite healthy, including those that have over-replicated blocks, under-replicated blocks, incorrectly replicated blocks, damaged blocks, and missing replicas.