Exec System Call in C

1. What is exec () system call?
2. What does exec () do in C?
3. What are the differences between execl () Execlp () Execle () and Execvp () system calls?
4. What does exec () return?
5. Is printf a system call?
6. What happens if you call exec before fork?
7. What happens if you call exec without using fork ()?
8. Does Exec create a new process?
9. What is the difference between fork () and exec ()?
10. Which is a system call 1 point execl () Execle () execve () Execv ()?
11. What does wait system call do?
12. How can I call one C program from another?

What is exec () system call?

The exec system call is used to execute a file which is residing in an active process. When exec is called the previous executable file is replaced and new file is executed. More precisely, we can say that using exec system call will replace the old file or program from the process with a new file or program.

What does exec () do in C?

The exec family of functions replaces the current running process with a new process. It can be used to run a C program by using another C program. It comes under the header file unistd. h.

What are the differences between execl () Execlp () Execle () and Execvp () system calls?

The function execl, execlp, and execle require each of the command line arguments to the new program to be specified as separate arguments. The execv, execvp and execve, we have to build an array of pointers to the arguments, and the address of this array is the argument to these three functions.

What does exec () return?

The exec functions replace the current process image with a new process image. The new image is constructed from a regular, executable file called the new process image file. There is no return from a successful exec, because the calling process image is overlaid by the new process image.

Is printf a system call?

Library functions might invoke system calls (e.g. printf eventually calls write ), but that depends on what the library function is for (math functions usually don't need to use the kernel). System Call's in OS are used in interacting with the OS. E.g. Write() could be used something into the system or into a program.

What happens if you call exec before fork?

fork starts a new process which is a copy of the one that calls it, while exec replaces the current process image with another (different) one. Both parent and child processes are executed simultaneously in case of fork() while Control never returns to the original program unless there is an exec() error.

What happens if you call exec without using fork ()?

exec without fork

The current process image is replaced with something different. Restarting the currently running program (might for example happen when you SIGHUP or such a server process, reloading everything and doing a completely fresh start).

Does Exec create a new process?

exec does not create a new process; it just changes the program file that an existing process is running. exec first wipes out the memory state of the calling process. It then goes to the filesystem to find the program file requested.

What is the difference between fork () and exec ()?

The fork() returns the PID of the child process. ... So the main difference between fork() and exec() is that fork starts new process which is a copy of the main process. the exec() replaces the current process image with new one, Both parent and child processes are executed simultaneously.

Which is a system call 1 point execl () Execle () execve () Execv ()?

Standard names of such functions in C are execl, execle, execlp, execv, execve, and execvp (see below), but not "exec" itself. The Linux kernel has one corresponding system call named "execve", whereas all aforementioned functions are user-space wrappers around it.

What does wait system call do?

A call to wait() blocks the calling process until one of its child processes exits or a signal is received. After child process terminates, parent continues its execution after wait system call instruction.

How can I call one C program from another?

use "system" a in-built function. Say you want to invoke another C program with name abc.exe. system("abc.exe"); // provide absolute path if exe place at other directory.