CMSC 125 - 5. Interlude: Process API

fork(), exec()

[Process creation and control in Unix]

• Uses ____ and ____ system calls

wait()

[Process creation and control in Unix]

• A process can wait for a process it has created using ______ system call

fork()

system call that creates a new process

address space, registers, PC

[fork()]

• The newly created process has its own private copy of the _______, _______, and _______.

0

What should the value of rc be to be determined as a child (new process)

int rc = fork();

<0

What should the value of rc be to be determined as fork failed

int rc = fork();

>0

What should the value of rc be to be determined as a parent of child

int rc = fork();

0, child PID

fork() returns ______ to the child process and the ______ to the parent process

non-deterministic, scheduler

[fork()]

The order of execution of the parent and child processes is _________, dependent on the _______

wait()

This system call won’t return until the child has run and exited

deterministic

Adding the call to wait() on the code block for the parent process guarantees the ______ order of execution

exec()

Run a program that is different from the calling program

code, static data

[exec()]

The child process will have different ____, _____, address space, registers, PC

• essential for building a shell

• It allows the shell to alter the environment of the about to be run program by exec(), enabling more features (ex. Pipes and I/O redirection) to be implemented

Why separate fork() and exec()?

an “interface” program that accepts commands from users to access the services of the OS

BASH, ZSH

examples of shells in Linux

Command Prompt, Powershell

examples of shells in Windows

kill()

used to send signals to a process

SIGINT

pressing CTRL+c

SIGSTOP

pressing CTRL+z

SIGCONT

fg command

Signals subsystem

________ enable the delivery of events to processes

signal handlers, signal()

Processes and process groups can have ______ (via ______ system call) to perform a specific action whenever a specific signal is received

users

Processes are associated to ______ in order to provide ownership and control, as well as limited security and protection

getuid()

system call to return the user id of the user of the process calling it

• main

• top/htop

• ps/pstree

• kill/killall

• fg/jobs

• /proc

Useful programs and commands in Linux terminal