Hi All

I had an interview , where the interviewer asked me the question
"How to create and call a process in unix"


I answered that we can use the command
FORK()/ CLONE() to create a process.

But I didnt have the answer for the second question, how to call a process.

Can someone help me with the second question ?

Thanks

Process is just a program in execution.

e.g. The set of lines written in the ls file is a program and when we type ls on the prompt, it gets called and thus the ls becomes a process which we called !!

and also you can use special system calls to call a program e.g. system (), execvp () and popen () etc.

IMHO

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System call is the services provided by Linux kernel. In C programming, it often uses functions defined in libc
which provides a wrapper for many system calls.

It is also possible to invoke syscall() function directly. Each system call has a function number defined in
<syscall.h> or <unistd.h>. Internally, system call is invokded by software interrupt 0x80 to transfer control to
the kernel. System call table is defined in Linux kernel source file “arch/i386/kernel/entry.S ”

System Call Example
#include <syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
int main(void) {
long ID1, ID2;
/*-----------------------------*/
/* direct system call */
/* SYS_getpid (func no. is 20) */
/*-----------------------------*/
ID1 = syscall(SYS_getpid);
printf ("syscall(SYS_getpid)=%ld\n", ID1);
/*-----------------------------*/
/* "libc" wrapped system call */
/* SYS_getpid (Func No. is 20) */
/*-----------------------------*/
ID2 = getpid();
printf ("getpid()=%ld\n", ID2);
return(0);
}