process 	- an execution environment that consists of
		  instruction, user-data and system data segments.
program 	- a file containing instructions and data used to
		  initialize instruction and user-data segments of a process.


                        
segmentation fault (SIGSEGV)
		- Indicates an attempt to access a memory address that is 
		  not part of the process virtual memory.  The address is
		  not mapped to an object or the writer has invalid permission.
		In C, this error usually is caused by a pointer error.
bus error (SIGBUS)
		- 1) an attempt to access a nonexistent physical device 
		  or bus address, perhaps caused by a hardware error.
		- 2) an attempt to make an incorrectly aligned transfer 
		  to an address.  Most machines require that a multi-byte 
		  transfer only go to certain addresses, such as a 4 byte 
		  transfer can only go to addresses that are multiples of 4.
		  In C, a typical cause is writing non-character data to
		  an odd address.
		In C, this error usually is caused by a pointer error.


stream		- full duplex data path in kernel between user processes
			and driver routines
		- similar to pipe except data flow and processing is 
                        bidirectional
effective UID 	- used to determine file access
		- same as read UID except is changed by setuid on file
session leader	- controlling terminal
process group	- subgroup of above

===

Somewhere it should be pointed out that there are two execution contexts 
for kernel:

process context:  kernel acts on behalf of process (e.g. getting date)
			exception handling: e.g. floating point exception;
                        synchronously.  Has access to u-area. May allowed to 
                        block.  Software interupts, system calls are other
                        examples.
system context:   kernel acts on behalf of system such as during interrupts.
                        Interrupts are asynchronous, caused by peripherals,
                        no process context - no access to u-area. Should not
                        block.