The document discusses Unix processes and process creation. It introduces the ps command for viewing processes, and explains that when a command is run, the shell process spawns a new child process to run it while suspending itself. Process creation uses the fork() system call to duplicate the calling process and the execlp() system call to load and execute the desired program. The wait() system call is used by the parent process to wait for a child process to complete.

1. Introduction to Unix and OS
Module 2 Continued……
Dr. Girisha G S
Dept. of CSE
SoE,DSU, Bengaluru

2. Agenda
• Process Basics
• ps command
• Mechanism of process creation
• Internal and External Command
• Process States and Zombies

3. The Shell Process
• A shell is simply a process
• Every time you issue a command, the UNIX operating
system starts a new process and suspends the current
process (the shell) until the new process completes.
Example: $ cat emp.lst

4. Parents and Childerns

5. ps - Process Status

6. ps command options

7. fork()
Syntax:
#include <unistd.h>
pid_t fork(void);
execlp()
Syntax:
#include <unistd.h>
int execlp(const char *file, const char *arg, …,
NULL );
wait()
Syntax:
#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(int * status);