1、 了解系統(tǒng)調(diào)用pipe()的功能和實(shí)際原理
2、 編寫一段程序，使用管道實(shí)現(xiàn)父子進(jìn)程之間的通信
a) 使用系統(tǒng)調(diào)用fork()創(chuàng)建一個(gè)子進(jìn)程
b) 子進(jìn)程調(diào)用函數(shù)write()向父進(jìn)程發(fā)送自己的進(jìn)程ID和字符串” s sending a message to parent.\n”。
c) 父進(jìn)程調(diào)用函數(shù)read()通過管道讀出子進(jìn)程發(fā)來的消息，將消息輸出屏幕，然后終止
xl2tpd a Layer 2 Tunneling Protocol (L2TP) daemon. It supports IPsec SA reference tracking, which enables the IPsec stacks to support multiple l2tp clients behind the same NAT router and multiple l2tp clients on the same internal IP address. It is a fork of "l2tpd".
Release focus: Minor feature enhancements
Changes:
Support for passwordfd, a workaround for some Cisco routers, and extended logging.
