... I get segmentation faults when accessing ports. ... Check the return value of ioperm() . Also, check that you're actually accessing the ports that you enabled with ioperm() (see Q3). If you're using the delaying macros ( inb_p() , outb_p() , and so on), remember to call ioperm() to get access to port 0x80 too. ... Check the order of the parameters; it should be outb(value, port) , not outportb(port, value) as is common in MS-DOS. ...