Filenames must consist of lowercase letters, numbers, periods (.), dashes (-), and underscores (_).
No file's name should ever begin with a dash, begin or end with a period, or contain multiple consecutive periods.
Individual components of a filename should be kept shorter than 50 characters. No filename should be longer than 100 characters. No directory should contain more than 100 entries.
Hard links and symlinks are prohibited unless they can be either removed or replaced with copies without ill effect.
These restrictions are intended to prevent file naming on the physical filesystem from causing problems with Unix shells, broken backup software, braindead physical filesystems, and untrained human operators.