Complex sentence: The book assumes a level of understanding of POSIX operating systems; their design, commands and permission controls and was made during the 3.4 release, thus some some information became dated within only a few months when the next OpenBSD version was released.
Split into simpler sentences: The book assumes a level of understanding of POSIX operating systems; their design, commands and permission controls. It was written at the time of the 3.4 release, thus some information became dated within only a few months when the next OpenBSD version was released.