# Illegal filenames

Every filesystem has its own set of characters that are not allowed in filenames. For example, HFS+ does not allow the use of '/' in filenames, though the operating system will transparently turn it into a ':' character if you use it when saving a file.

When you are copying a file between different filesystems, it is possible that a filename that is perfectly legal on one filesystem will be illegal on the other. When Synk attempts to copy this file, it will not be allowed to create the file and will generate an illegal filename error.

To fix this problem, you should name your files with names that are valid on all filesystems you will be working with. To be truly safe, you should stick to just letters and numbers.