信号机制是解决进程同步和互斥的有效工具。实现进程间的互斥时，公用变量信号的初值一般设置为(15)；实现进程间的同步时，私用变量初值一般设置为(16)。

(54)

(71)

(72)

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(67)

Networks can be interconnected by different devices in the physical layer networks can be connected by (71) or hubs．which just move the bits from one network to an identical network．One layer up we find bridges and switches which operate at data link layer．They can accept (72) ，examine the MAC address and forward the frames to a different network while doing minor protocol translation in the process in me network layer，we have routers that can connect two networks，If two networks have (73) network layer，the router may be able to translate betweenthe packer formats．In the transport layer we find transport gateway，which can interface between two transport connections Finally，in the application layer，application gateways translate message (74) ．As an example，gateways between Internet e-mail and X，400 e-mail must (75) thee-mail message and change various header fields．

(68)

配置WWW服务器是Linux操作平台的重要工作之一，而Apache是目前应用最为广泛的Web服务器产品之一，(48)是Apache的主要配置文件。如果允许以“http://www.xxx.edu.cn/-usemame”方式访问用户的个人主页，必须通过(49)指令设置个人主页文档所在的目录。

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(65)

若FTP地址写为ftp://test:123@222.18.8.241:8901，则该地址中的“test”的含义是FTP服务器的(42)。若FTP地址为ftp://222.18.8.241，则该地址对应连接的FTP服务器用户名字为(43)。

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