wait() system call

 

⚙️ The wait() System Call

Purpose:

The wait() system call is used by a parent process to pause execution until one of its child processes terminates.

This ensures synchronization — the parent process continues only after the child has completed its work.

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Syntax:

pid_t wait(int *status);

• Return value:

  • Returns the process ID of the terminated child on success.

  • Returns -1 if there are no child processes.

• Parameter:

  • status is an integer pointer used to store the exit status of the child.

  • You can pass NULL if you don’t need it.

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Behavior:

• When the parent calls wait(), it is blocked until a child process finishes execution.

• Once the child terminates, the parent resumes.

• This avoids zombie processes, since wait() collects the child’s exit status.

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Example:

pid_t pid = fork();

if (pid == 0) {
    // Child process
    printf("Child process running\n");
}
else {
    // Parent process waits
    wait(NULL);
    printf("Parent process running after child\n");
}

Output:

Child process running
Parent process running after child

✅ Here, wait() ensures synchronization — the parent executes only after the child finishes.