Module 5

Question 1

Redirection

Answer 1

modifying the location to which an input is taken from or an
output is sent for a given command; redirection operators are commutative,
meaning they can appear in swapped orders and produce the same result
○ “dup2” system call: implement redirection by passing in two file
descriptors (oldfd and newfd) and causing newfd to point to the file or
data structure that was pointed to by oldf

Question 2

Standard input

Answer 2

the location where programs look for their inputs; for
programs initiated in command-line, this defaults to your terminal; Standard in
can be redirected, and child processes inherit standard in from their parent
process; the Standard in file descriptor is “0”

Question 3

Standard output

Answer 3

the location where programs stream their outputs; for
programs initiated in command-line, this defaults to your terminal; Standard
out can be redirected, and child processes inherit standard out from their
parent process; the Standard out file descriptor is “1”

Question 4

Pipe

Answer 4

a form of interprocess communication, providing a way to stream data
from one process to the other; pipes have a “write end” to which data gets
written by one process to be sent to another process, and a “read end” from
which the receiving process reads the incoming data

Question 5

SIGPIPE

Answer 5

a signal generated when a process tries to write to a pipe whose
read end has been closed

Question 6

Process pipelining

Answer 6

running multiple processes at the same time where the output
of one process is used as input to another process

Question 7

Half duplex

Answer 7

data flows in one direction; pipes between two processes are in the half
duplex communication paradigm as data flows in one direction between the two
processes

Question 8

FIFO

Answer 8

these are similar to pipes; while pipes are temporary and unnamed
connections, FIFOs are files with names that allow two processes to communicate by
writing to the file

Question 9

Process group

Answer 9

collection of processes that are established in a way such that you
can send (or block) a signal to the entire group at the same time; the processes in a
pipeline are in a single process group

Question 10

PGID

Answer 10

process group ID

Question 11

Session ID

Answer 11

one instance of your login to your shell is a session, and all processes
launched in this session have the same session ID

Question 12

SSH

Answer 12

a secure network protocol that allows a remote user to be authenticated to
login to a machine

Question 13

Foreground process

Answer 13

there is always exactly one foreground process; this process
has access to interactive shell output (in the absence of explicit redirection) and
input, and receives all the terminal generated signals; the shell must wait on this
process before executing another process

Question 14

Job terminal control

Answer 14

ability to manipulate multiple jobs from a single terminal and
also to allow us to toggle jobs between background and foreground

Question 15

Synchronous waiting

Answer 15

a process waits finds out the outcome of another process by
implementing a loop that constantly checks for a signal; “busy wait”

Question 16

Asynchronous waiting

Answer 16

a process continues executing normally and when another
process has a signal to send, a generic SIGCHLD is sent to the executing process,
who handles the signal with a SIGCHLD signal handler

Question 17

Background processes

Answer 17

there can be any number of background processes; these
processes will allow the user to execute other programs and interact with the shell
without waiting