说明：  模拟unix操作系统中的文件系统功能，在终端界面上用户可以象unix的shell命令一样输入一些命令，如输入ls 显示文件目录，chmod改变文件权限，chown改变文件拥有者，chgrp改变文件所属组，chnam改变文件名，pwd显示当前目录，cd改变当前目录，mkdir创建目录，rmdir删除目录，mk创建文件 ,cp文件拷贝，rm删除文件，cat显示文件内容，login切换用户，passwd修改用户口令 等功能。在后台，要实现混合索引式文件结构，包括用空闲结点号栈管理空闲结点和成组链接发管理空闲盘块。
(Simulation of unix operating system file system functions, in a terminal interface as unix users, like the shell command to import some orders, such as the input file directory ls show, chmod to change file permissions, chown change file owner, chgrp to change the file belongs to group chnam change the file name, pwd show current directory, cd to change the current directory, mkdir to create directories, rmdir delete directory, mk create a file, cp file copy, rm to delete files, cat shows the contents of the documents, login to switch user, passwd modify user passwords and other functions . In the background, it is necessary to realize a mixed-type index file structure, including its stack node idle idle node management and group management links fat free disk blocks.)