unix

Unix does process creation/change using-

fork() and exec...()

What does fork1.c do?-

fork() then say hello

pid-

process ID

fork1a.c-

fork() and print pid

fork1b.c-

fork() and print relationship

fork2.c-

fork() twice creating 4 processes

fork3.c-

fork() thrice creating 8 processes

what happens when a parent forks-

creates a child class, calls exec(), exit(), wait(), then back to parent

mathtable.c-

uses 10 children to print ten lines of a multiplication table

in mathtable.c, how did the program wait before creating the next child-

wait(NULL)

can two process read and write from one pipe-

yes

do you have to close extra pipes if you allocate different pipes for reading and writing to different processes-

no

why would you close extra pipes if you allocate different pipes for reading and writing to different processes-

to prevent confusion of reading or writing a wrong pipe

guess3.c-

Parent and child processes communicate with each other using pipes, a special extension of file descriptors.

what happens if you create a pipes then fork-

the pipes get shared by the child

guess5.c-

switches user functionality to a different

What do the exec functions return on error?

-1

FD 0

Standard Input

FD 1

standard output

fd 2

error output

if pipes 0 1 and 2 are taken, what will a new pipes fds id be

3 and 4

what is the input pipe fds id

0

what is the output pipe fds id

1

guess6.c

reduced to do the pipe setup then fork(), then adjust thepipes using close() and dup(), theninvoke computer & user programs

if you need a 2nd input parameter what fds id would it be

3

mysum.c

uses multiple pipes between the addition child class

Assignment 8

calculator that uses many different pipes between the child classes that do the different processes. pipes are created dynamically based on where the data needs to go

ps -ef

Command to see every process on the system using standard syntax

ps -f

uid, pid, ppid, c (cpu), stime (start time), tty, time, cmd

popen()

Opens a pipe to read or write to

execvp

"parameters (const char *filename, char *const argv[]); searches directories listed in PATH environment to find full name of a file from filename; can execute system utility programs; array of pointers must be terminated by NULL poitner"

pclose()

Closes a pipe opened by popen() returns status

do unnamed pipes need to be created by common ancestors and passed to children

yes

what is the advantage of named pipes

does not need to be created by ancestors and can be used to connect any two processes

qserver.c & qclient.c

Server creates a named pipe and wait for requests from clients. Clients open server FIFO and send its own FIFOFor each client request, server opens specified FIFO and writes a quote & closes.

qserver2.c & qclient2.c

Avoid race conditions - good to include \n at the end of each lineMake server independent of client misbehavior by making the server wait for the client

qserver3.c & qclient3.c

Each client can ask for multiple quotes! But make the server work with old clients too.

qserver4.c & qclient4.c

Enable server and client to have a conversation:client can repeatedly specify quote number, server can respond....\n at end of each line and fflush() are needed to avoid buffering glitches.

how many clientfifos are needed if there are n clientes

n

how many serverfifos are there if there are n clients

1

Multiple writers for same pipe is OK, but what about multiple readers?

no

Assignment 10

hangman game that uses client and server fifos to get multiple client guesses at the same time

messages

IPC mechanism that uses servers and client to send an receive food

shared memory

In interprocess communication, a section of memory shared by multiple processes and used for message passing.

shmget()

create/recreate

shmat()

attach

shmdt()

detatch

shmctl()

change/remove

Unique key in shared memory

needed for the programs to create/access the shared memory

What do the exec functions return on success?

nothing

in guess 5 how does the child become a new process

execl()

socket() client or server

both

bind() client or server

both

recvfrom() client or server

client

read() client or server

client

close() client or server

both

listen() client or server

server

read() client or server

server

write() client or server

server

ps -ef

Shows all process ID

accept() client or server

server

Difference between TCP and UDP?

TDP is slow but secure while UDP is fast but not secure.

Are sockets unidirectional or bidirectional?

birectional

Server: server5 bound to port \#NNNN

ncat server port user1

What to put on top of bash script?

\#! /bin/bash

Full form of bin?

Binary