How To Run A Process From Another Process? [using system() function]

We know that Linux or Unix-like Operating System is a multi-tasking Operating System and an instance of a program constitutes a process.

In Linux, multiple processes can run simultaneously. Even multiple instances of the same program can execute simultaneously. Moreover, a process may initiate another process.

In the following example, we will discuss how a process can be executed from another process.

---

To discuss this topic, first, we should understand that when we run a command, a process is started. For example, if we execute ls command, a process is being started, which will be enlisted an in-process list of the Operating System.

If we run a C program, it will create another process. Hence, if we perform a system call from within a program, two processes will be executed.

---

In the following program, we have shown how ls -l command can be executed from a C program.

Source code to run a process inside another process

#include <stdlib.h> #include <stdio.h> int main() { printf("Running ls with system\n"); system("ls -l"); printf("Done.\n"); exit(0); }

---

In the above example, we have executed a process using ls -l command. After the call of the system function, the main process waits until the process gets completed. Hence, the Done message is printed after printing the output of the command.

---

In this context, if you want to run a process as a background process and you want to terminate the main process after starting another process, you can use & symbol at the end of the command you want to run. The example is shown below.

Source code to run a process inside another process

#include <stdlib.h> #include <stdio.h> int main() { printf("Running ls with system\n"); system("ls -l &"); printf("Done.\n"); exit(0); }

If you look at the output, you will understand that the main process is being terminated before the completion of another process.

Happy Exploring