1. 创建进程fork

fork创建一个子进程，给新进程分配资源（数据和代码空间）

#include <unistd.h>

pid_t fork(void);

函数返回值，给子进程返回0，给父进程返回子进程的ID，

• 0 to the child process

• the process ID of the child process to the parent process.

• -1 to the parent process, no child process is created

fork运行原理如下：

2. vfork

vfork，创建一个子进程，并阻塞父进程（block parent），

#include <unistd.h>

pid_t vfork(void);

fork与vfock区别，

• vfork creates a child process and block parent (the calling thread is suspended until the child terminates)
• vfork() is a special case of clone(2). It is used to create new processes without copying the page tables of the parent process. It may be useful in performance-sensitive applications where a child is created which then immediately issues an execve(2).