closefrom.3bsd man page
closefrom — delete open file descriptors
#include <unistd.h> (See libbsd(7) for include usage.)
The closefrom() system call deletes all open file descriptors greater than or equal to lowfd from the per-process object reference table. Any errors encountered while closing file descriptors are ignored.
The closefrom() function first appeared in FreeBSD 8.0.