1. system启动的子进程回挂起，直到子进程正常退出，或者kill掉。

2. 使用kill命令kill子进程

void *thr_fn1(void *arg){        system("ffmpeg -re -i master.mp4 -c copy -f flv -y /dev/null");        printf("son pro exit\n");}void *thr_fn2(void *arg){        sleep(10);        system("ps -ef | grep /dev/null | grep -v grep | cut -c 9-15 | xargs kill -s 9");}int main(){        int     err;        err = pthread_create(&ntid, NULL, thr_fn1,0);        if(err!=0)        {                printf("can't create thread\n");                exit(1);        }        err = pthread_create(&ntid, NULL, thr_fn2,0);        if(err!=0)        {                printf("can't create thread\n");                exit(1);        }        while(1)        {                sleep(1);        }        sleep(3);        exit(0);}