return value of fork() system call can be

Then in the next line we have created an array of character pointers. Therefore in child process value of x remain 6 but then child process modified the value of x to 10. On failure, -1 is returned in the parent, no child process is created, and errno is set appropriately. This is because control is never returned back to old process image once new process image replaces it. 345 views The entire content of the process is replaced with a new program.The user data segment which executes the exec() system call is replaced with the data file whose name is provided in the argument while calling exec().The new program is loaded into the same process space. The following variant of the Hello World program demonstrates the mechanics of the fork system call in the C programming language. She can be found on Facebook at 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. Following is the simple syntax for this function − fork Return Value.

Fork() returns a zero to the newly created child process. fork() vs exec() The fork system call creates a new process. System call fork()is used to create processes. Hence there is no concept of parent and child processes in exec() system call.In fork() system call the parent and child processes are executed at the same time. in the middle of a Writing tutorials and creating programs is her passion. The last element of this array should be NULL as the terminating point.Then we have used the function execv() which takes the file name and the character pointer array as its argument. But in exec() system call, if the replacement of process image is successful, the control does not return to where the exec function was called rather it will execute the new process. The explain_fork function is used to obtain an explanation of an error returned by the fork(2) system call. By default, waitpid() waits only for terminated children, but this behaviour is modifiable via the options argument, as described below. 6. "While the 4.4BSD implementation got rid of the vfork implementation, causing vfork to have the same behavior as fork, it was later reinstated in the In the child process, the return value appears as zero (which is an invalid process identifier). It should be noted here that we have used ./ with the name of file, it specifies the path of the file. You must ensure that you wait on your children to prevent "zombie" processes from forming. Total Number of Processes = 2So there are total eight processes (new child processes and one original process).If we want to represent the relationship between the processes as a tree hierarchy it would be the following:In the above code, a child process is created. A message is displayed and we have used execv() system call and the current child process image which is example.c will be replaces with hello.c. Below are different values returned by fork().The number of times ‘hello’ is printed is equal to number of process created. Ayesha Tariq is a student of Computer Science and working as a freelancer as well. Positive Value: The positive value is returned to the parent process. If fork () call is successful then code after this call will be executed in both the process. #include pid_t fork (void); Return value On success, the PID of the child process is returned in the parent, and 0 is returned in the child. Syntax. Don’t stop learning now. For a process to start the execution of a different program, it first forks to create a copy of itself. Zero Value: It returns Zero for the newly created child process. We use cookies to ensure you have the best browsing experience on our website. The BSD man page states: "This system call will be eliminated when proper system sharing mechanisms are implemented. 3. Whereas, exec() system call is used to replace a process image with a new process image. The fork system call creates a new process. When the process image is successfully replaced nothing is returned to calling function because the process that called it is no longer running.

If it return -1 (negative value) then it means child process doesn’t create and it has an error.

2. This is because example.c is the parent process image and hello.c is the child process image.

Signal handlers are inherited, but not shared. In the above example we have used the type pid_t which will store the return value of fork (). in unix or echo %ERRORLEVEL% in windows after executing the same command in a shell.