1、简单认识操作系统
1-1：
cornerstone 基石
kernel 核心
provied 提供
interface 界面，接口
interact 交互
1-2：Simple classification（分类） of operating systems
a variety of 各种
kernel 内核
Windows：单用户
unix：最早的multi-user, multi-tasking 多用户多任务的分时操作系统。
linux：是免费开源的类Unix操作系统，可以安装在各种计算机硬件系统中，比如平板（tablets）路由器（routers）
2、exploration（探索） of Linux
Kernel version（内核版本）：
linux不是一个操作系统，他只是一个kernel（内核），
kernel：建立硬件和软件间的通讯平台,提供虚拟存储等功能
Release version（发行版本）：一些公司基于linux内核进行2次开发后的版本，比如Ubuntu和CentOS（新手推荐）
3、Linux file system overview。 linux文件概述
3-1、all resources managed by the operating system。
input and output devices（输入输出设备）or directories（目录） are considered as（被视为） one file.
embodiment ：体现
this is an embodiment of the UNIX philosophy, Unix物理哲学的体现。so this concept（思想） has also been passed down（传承下来）
treated ：对待，视为.
In UNIX systems, all resources are treated as files, including hardware devices. UNIX systems treat each piece of hardware as a file, usually called a device file, so that users can access the hardware by reading and writing files.Unix把所有的硬件都看做文件，称为设备文件，因此用户可以通过读写文件的形式访问硬件。
3.2 File types and directory structures
（1）普通文件：符号是 -
（2）目录文件：符号是 d
（3）字符设备文件：符号是c
（4）块设备文件：符号是b
（5）符号链接文件：符号是l
常见目录描述：
/bin：存储（2进制可执行文件）binary executable files (ls, cat, mkdir, etc.)，commonly used commands are generally here;常用命令通常都在这里。
/ etc: Stores system management and configuration files;存储系统管理和配置文件。
/ home: The root directory that stores all user files（存储所有用户的文件和根目录）, which is the base point of the user’s home directory（是用户主目录的根节点）. For example, the user user’s home directory is / home / user, which can be expressed by ~ user;（/home/user == ~user）
/ usr: used to store system applications;存储系统应用程序
/ opt: Where to place additional installed optional application packages. （放置额外安装的可选程序包）In general, we can install tomcat, etc. here;
/ proc: Virtual file system directory, which is a mapping of system memory.(虚拟文件系统目录，系统内存的映射) You can directly access this directory to get system information（您可以直接访问这个目录来获取系统信息）;
/ root: the home directory of the superuser 超级用户的主目录(system administrator) (privileged class ^ o ^);
/ sbin: Stores binary executable files, which can only be accessed by root.（存储只能由根用户访问的文件） Stored here are system-level management commands and programs used by system administrators. Such as ifconfig（系统级的管理命令）
/ dev: used to store device（设备文件） files;
/ mnt: The installation point where the system administrator installs the temporary（临时文件） file system. The system provides this directory for users to temporarily mount （挂载）other file systems.（系统规定此目录供用户临时挂载其他文件系统）
/ boot: stores various files used during system boot;存储系统引导期间使用的各种文件
/ lib: Stores library files related to system operation;存储与系统操作相关的库文件
/ tmp: used to store various temporary files, and is a common temporary file storage point;用于存储各种临时文件，是常用的临时文件存储点
/ var: It is used to store the files that need to be changed during operation. It is also an overflow area for some large files, such as log files of various services (system startup logs, etc.), etc .;它用于存储在操作期间需要更改的文件。它也是一些大型文件的溢出区域，如各种服务的日志文件(系统启动日志等)等
/ lost + found: This directory is usually empty, and the system shuts down abnormally and leaves a “homeless” file (what is called .chk under windows) here.这个目录通常是空的，系统异常关闭并留下一个“无家可归”的文件(在windows下称为.chk)
