chmod is an abbreviation for the term "change mode". chmod is a function on all Unix, Linux and FreeBSD systems that allows varying levels of permissions to be set on files and directories in relation to the application attempting to access them. chmod controls the configuration of execute, write and read accessibility (permissions). For people using an FTP application for chmod, it can be difficult when a script author only states that a particular file needs permissions of, for example, 755 - some FTP applications only present a dialog box with checkboxes for Read, Write and Execute. Using the table above can make it easier for you to know which boxes should be checked. Here are some examples of common chmod settings: