mysql_fix_extensions converts the extensions for MyISAM (or ISAM) table files to lowercase. It looks for files with an extension that that matches any lettercase variant of .frm, .myd, .myi, .isd, and .ism and renames them to have extensionsn of .frm, .MYD, .MYI, .ISD, and .ISM, respectively. This can be useful after transferring the files from a system with case-insensitive filenames (such as Windows) to a system with case-sensitive filenames.

Invoke mysql_fix_extensions like this, where data_dir is the pathname to the MySQL data directory.

shell> mysql_fix_extensions data_dir