课程作业
1.按系列罗列Linux的发行版，并描述不同发行版之间的联系与区别。
Linux是一种类unix的系统，不同的发行版主要就是对Linux的不同版本的内核和GUN组织的开源的的软件进行打包形成了不同发行版的系统。
主流的发行版有S.U.S.E、Debian、Geetoo、Arch、Redhat等等
在从基础上还会发行了很多二次发行版，比如，基于Debian的Ubuntu、Knopix，基于Redhat的Centos、Fedora、Oracle。
2.安装Centos7.6操作系统，创建一个自己名字的用户名，并可以正常登录，将主要步骤截图。
使用VMware安装Centos虚拟机，我这里安装的是centos7.7，系统可以在阿里云开发者社区下载，网站是https://developer.aliyun.com/mirror](https://developer.aliyun.com/mirror
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在主界面点击创建新的虚拟机
image.png - 在创建向导中先选择自定义-稍后安装操作系统-选择版本CentOS7-要创建的位置-选择处理器数量和内存数量以及网络模式-磁盘类型和容量，完成之后在主界面选择此虚拟机的CD/DVD设置，选择我们要安装的系统镜像，然后开启此虚拟机。
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image.png - 开启虚拟机后使用root用户登录进系统，开始创建用户。
使用useradd username添加用户，使用passwd username来设置用户登录密码。
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再使用logout命令推出root用户登录，使用刚刚设置的用户名和密码登录。
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3.配置环境变量，实现执行history的时候可以看到执行命令的时间。 -
未配置环境变量时：
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使用vim对用户的环境变量文件：家目录下的.bashrc文件
image.png - 在末尾加上history的格式的变量HISTTIMEFORMAT的设置，其值设定为“%F %T ”，如图：
image.png - 再使用命令source来重新读取环境变量文件，
source ~/.bashrc，再执行history时就会显示出时间和日期了。
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4.总结Linux哲学思想。 - 一切皆文件，它将几乎所有的资源抽象为文件的形式，甚至包括硬件设备。
- 它是由众多功能单一的程序组成的，讲求一个程序只做好一件事，通过组合来完成复杂任务。
- 它尽量避免和用户交互，从而易于用编程的方式来实现自动化任务。
- 使用文本文件保存配置信息
5.总结Linux常用命令使用格式，并用实例说明。
命令基本格式都常见为COMMAND...[OPTIONS]...[ARGUMENTS]，指的是命令接上它的可选运行特性再接上它的作用对象。
如ls命令，他的作用是列出作用对象下的所有文件。查看其help，发现他有多种options,如常见的-a可显示全部包括隐藏的文件，-l以列表的形式显示文件等等。然后在之后接上它的作用对象就是目录，如列出/etc目录下的所有文件，ls -a /etc。命令用很多，并不能都记住其用法，注意在使用时查看其帮助，了解他的多种可选特性即可。
[root@wang ~]# ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
Mandatory arguments to long options are mandatory for short options too.
-a, --all do not ignore entries starting with .
-A, --almost-all do not list implied . and ..
--author with -l, print the author of each file
-b, --escape print C-style escapes for nongraphic characters
--block-size=SIZE scale sizes by SIZE before printing them; e.g.,
'--block-size=M' prints sizes in units of
1,048,576 bytes; see SIZE format below
-B, --ignore-backups do not list implied entries ending with ~
-c with -lt: sort by, and show, ctime (time of last
modification of file status information);
with -l: show ctime and sort by name;
otherwise: sort by ctime, newest first
-C list entries by columns
--color[=WHEN] colorize the output; WHEN can be 'never', 'auto',
or 'always' (the default); more info below
-d, --directory list directories themselves, not their contents
-D, --dired generate output designed for Emacs' dired mode
-f do not sort, enable -aU, disable -ls --color
-F, --classify append indicator (one of */=>@|) to entries
--file-type likewise, except do not append '*'
--format=WORD across -x, commas -m, horizontal -x, long -l,
single-column -1, verbose -l, vertical -C
--full-time like -l --time-style=full-iso
-g like -l, but do not list owner
--group-directories-first
group directories before files;
can be augmented with a --sort option, but any
use of --sort=none (-U) disables grouping
-G, --no-group in a long listing, don't print group names
-h, --human-readable with -l, print sizes in human readable format
(e.g., 1K 234M 2G)
--si likewise, but use powers of 1000 not 1024
-H, --dereference-command-line
follow symbolic links listed on the command line
--dereference-command-line-symlink-to-dir
follow each command line symbolic link
that points to a directory
--hide=PATTERN do not list implied entries matching shell PATTERN
(overridden by -a or -A)
--indicator-style=WORD append indicator with style WORD to entry names:
none (default), slash (-p),
file-type (--file-type), classify (-F)
-i, --inode print the index number of each file
-I, --ignore=PATTERN do not list implied entries matching shell PATTERN
-k, --kibibytes default to 1024-byte blocks for disk usage
-l use a long listing format
-L, --dereference when showing file information for a symbolic
link, show information for the file the link
references rather than for the link itself
-m fill width with a comma separated list of entries
-n, --numeric-uid-gid like -l, but list numeric user and group IDs
-N, --literal print raw entry names (don't treat e.g. control
characters specially)
-o like -l, but do not list group information
-p, --indicator-style=slash
append / indicator to directories
-q, --hide-control-chars print ? instead of nongraphic characters
--show-control-chars show nongraphic characters as-is (the default,
unless program is 'ls' and output is a terminal)
-Q, --quote-name enclose entry names in double quotes
--quoting-style=WORD use quoting style WORD for entry names:
literal, locale, shell, shell-always, c, escape
-r, --reverse reverse order while sorting
-R, --recursive list subdirectories recursively
-s, --size print the allocated size of each file, in blocks
-S sort by file size
--sort=WORD sort by WORD instead of name: none (-U), size (-S),
time (-t), version (-v), extension (-X)
--time=WORD with -l, show time as WORD instead of default
modification time: atime or access or use (-u)
ctime or status (-c); also use specified time
as sort key if --sort=time
--time-style=STYLE with -l, show times using style STYLE:
full-iso, long-iso, iso, locale, or +FORMAT;
FORMAT is interpreted like in 'date'; if FORMAT
is FORMAT1FORMAT2, then FORMAT1 applies
to non-recent files and FORMAT2 to recent files;
if STYLE is prefixed with 'posix-', STYLE
takes effect only outside the POSIX locale
-t sort by modification time, newest first
-T, --tabsize=COLS assume tab stops at each COLS instead of 8
-u with -lt: sort by, and show, access time;
with -l: show access time and sort by name;
otherwise: sort by access time
-U do not sort; list entries in directory order
-v natural sort of (version) numbers within text
-w, --width=COLS assume screen width instead of current value
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line
SELinux options:
--lcontext Display security context. Enable -l. Lines
will probably be too wide for most displays.
-Z, --context Display security context so it fits on most
displays. Displays only mode, user, group,
security context and file name.
--scontext Display only security context and file name.
--help display this help and exit
--version output version information and exit
SIZE is an integer and optional unit (example: 10M is 10*1024*1024). Units
are K, M, G, T, P, E, Z, Y (powers of 1024) or KB, MB, ... (powers of 1000).
Using color to distinguish file types is disabled both by default and
with --color=never. With --color=auto, ls emits color codes only when
standard output is connected to a terminal. The LS_COLORS environment
variable can change the settings. Use the dircolors command to set it.
Exit status:
0 if OK,
1 if minor problems (e.g., cannot access subdirectory),
2 if serious trouble (e.g., cannot access command-line argument).
GNU coreutils online help: