slides05

Question 1

three streams in a process

Answer 1

• standard in (stream 0): default stream for input on keyboard
• standard out (stream 1): eg. terminal screen
• standard error (stream 2)

Question 2

File Descriptor Table

Answer 2

• each process has a unique FDT in the kernel space
• cloned during a fork
• index: File Descriptor
• 0th entry: stdnin
• 1st entry: stdout
• 2nd entry: stderr

Question 3

output redirection (printing to a file)

Answer 3

• close(1) dissociates FTD[1] from the terminal
• FDT[1] becomes available for use
• if we run int fd = open(“abc.txt”, ), we get fd = 1 (it looks for the first available slot from the top of FTD)
• now, whenever we call printf(), instead of displaying to the terminal, it will go into the file ‘abc.txt’
• the redirection is only valid for the current process, you can create a child at this point and it will inherit the redirection

Question 4

intput redirection

Answer 4

1. close(0)
2. open the file from which we want to receive the scanf() inputs

Question 5

command piping

Answer 5

• one process sends its output so it becomes an input to another process
• done using pipes

Question 6

pipe()

Answer 6

• creates a pipe
• two end points
• unidirectional data flow
• write end: pipe[1]; read end: pipe[0]
• inside the kernel, array of two fd descriptors

Question 7

sharing information between parent and child processes using pipe

Answer 7

• when you do a fork: FTD is copied to child process, pipe is exact same in both processes (not a copy)
• REVIEW

Question 8

socket

Answer 8

• endpoint provided by OS for communication
• pair of sockets acts as a communication link between processes
• identified by an address:port