102-多进程的ping

没有多进程，ping一个网段的IP地址往往要花费几十分钟；使用多进程，几秒钟解决。

import subprocess
import os

def ping(host):
    rc = subprocess.call(
        'ping -c2 %s &> /dev/null' % host,
        shell=True
    )
    if rc:
        print('%s: down' % host)
    else:
        print('%s: up' % host)

if __name__ == '__main__':
    ips = ('192.168.1.%s' % i for i in range(1, 255))
    for ip in ips:
        pid = os.fork()
        if not pid:
            ping(ip)
            exit()