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Knowledge of Linux

Linux, full name GNU/Linux, is a free-to-use and free-to-spread UNIX-like operating system. Its kernel was first released on October 5, 1991 by Linus Bennard Torvalds. Inspired by Minix and Unix ideas, it is a POSIX-based multi-user, multi-tasking, multi-threaded and multi-CPU operating system. It runs the major Unix tools, software, applications, and network protocols. It supports both 32-bit and 64-bit hardware. Linux inherits the design idea of Unix taking network as the core, and it is a multi-user network operating system with stable performance. There are hundreds of different distributions of Linux, such as community-based debian, archlinux, and commercial-based Red Hat Enterprise Linux, SUSE, Oracle Linux, etc.

Main Catalogue

Linux system is a multi-user operating system, only a root directory/, no drive letter concept.

• /

  The root directory, generally only the directory is stored under the root directory. Entering/home in the terminal is actually telling the computer to start with/(I .e. the root directory) and then enter the home directory;

• /bin,/user/bin

  Directories of executable binary files, such as commonly used commands: ls,tar,mv,cat, etc;

• /boot

  Place some files used when the Linux system starts, such as Linux kernel file:/boot/vmlinuz, system boot manager:/boot/grub;

• /dev

  Store the device files under the Linux system and access a file under the directory, which is equivalent to accessing a device. The commonly used optical drive is mount /dev/cdrom /mnt;

• /etc/

  It is not recommended to store executable files in this directory. Important configuration files are:/etc/initab etc/fstab etc/init.d /etc/xll /etc/sysconfig/xinetd.d;

  • passwd

  Store the user's information, consisting of 6 semicolon

  用户名: 密码:UID:GID: 用户全名: 家目录: 登录命令
  密码：x 表示加密的密码 密码存放在 /etc/shadow
  UID：用户标识
       普通用户从 1000 开始 用户权限由 UID 决定
       root 用户为 0 如果把某一用户的 UID 改成 0 那么他具有 root 权限
  GID：组标识

  • shadow

  存放密码信息 是 /etc/passwd 的影子文件

  用户名: 加密密码: 最后一次更改密码时间: 天数

  • group

  Store group information

  组名: 密码:GID: 包含的用户

  • gshadow

  is a shadow file of/etc/group

  组名: 密码: 管理者: 组群成员

• /home

  The default user's home directory. When a user account is added, the user's home directory is stored in this directory: ~ indicates the home directory of the current directory, and ~ edu indicates the home directory used for edu;

• /lib,/user/lib,/usr/local/lib

  The directory of the function library used by the system. During the execution of the program, some additional parameters need to be called;

• /lost fount

  When a system exception generates an error, some missing fragments will be placed in this directory;

• /mnt,/media

  The default mount point of the disc. Usually, the disc is mounted under/mnt/cdrom, but not necessarily. You can select any location to mount the disc;

• /opt

  Directory for additional installation software;

• /proc

  The data in this directory are all in memory, such as the system core external equipment and network status. Since the data are all stored in memory, it does not occupy disk space. The more important files are:/proc/cpuinfo,/proc/interrupts,/proc/dma,/proc/ioports,/proc/net/*, etc;

• /root

  The home directory of the system administrator root.

• /usr/share/doc

  Contains a complete series of software documentation

Home Directory

• ~/.ssh/

  Directory where ssh information is stored

  • config

  Information for configuring ssh

  Configure Alias

  Host <别名>
      HostName 
      User <用户>
      Port <端口>

  • known_hosts

  Saves recorded server information

  • authorized_keys

  Authenticated public key information

  • id_rsa

  Generated private key information

  Generating private and public keys on the connection side

  Copy the public key to the server

  You can log in to the server without confidentiality.

  • id_rsa.pub

  Generated public key information

  Give the public key to the server

  You can log in to the server without confidentiality.

• ~/.bash

  • ~/.bash_history

  Command History File

  All previously executed commands will be saved here

  • ~/.bashrc

  The bash command that is executed every time you log in

Environment Variables

• Viewing Environment Variables: env

• Setting System Environment Variables

  export name="值"
  #（注意：这只是临时设置环境变量，在下次登录 shell 时就失效了）# 永久方法：#  在 /etc/profile.d 目录下创建 sh 文件
  #  在每次登录 shell 时都会执行 /etc/profile.d 文件夹里面的所有 sh 文件

Command

Command format:

    command [-options] parameter

    command -lhand command -l -h The effect is the same

Query Help:

    command --help

    man command

Shortcut Keys:

    Tab auto-completion

    ↑ / ↓ Quick Switch History Command

    Ctrl C to exit the selection and cancel the current command

Users and Permissions

Super User

• rootThe account is a super user account.

• For system maintenance and management

• Directly using Super User is not recommended

User Symbol

permission symbol

Commonly used software packages

About Shell

Wildcard

Asterisk *

Use to match any character, including numbers, letters, and symbols. You can use an asterisk to specify any character that the application needs to find in the corresponding position of the character.

# 删除所有文件后缀为.bak 的文件
rm *.bak

Question mark?

Used to match a single arbitrary character.

# 列出所有任意一个字符开头，后面为 bc.txt 的文件
# 例如：abc.txt bbc.txt 1bc.txt
ls ?bc.txt

File Alias

# 给命令设置别名
# alias < 别名 >="< 原命令 >"
alias test="ls -l /"
# 取消别名
# unalias < 别名 >
unalias test

Piping

# 管道的符号为 |
[命令]|[命令]|[命令]

Redirect

# 输出重定向
# 将命令执行的输出保存在文件里 直接覆盖
[命令] > [文件]
ls /etc > 1.txt
# 追加重定向
# 追加来替代直接覆盖文件
ls /etc >> 1.txt

# 输入重定向
[命令] < [文件]
grep test < 1.txt
# 追加重定向
# 获取一段分隔符之间的内容
[命令] << [分隔符]
> [内容]
> [内容]
> [分隔符]

# 错误重定向
# 把命令发生的错误写到文件里
[命令] 2> [文件]
ls /nofile 2> 1.txt
ls /nofile 2>> 1.txt

# 同时实现输出和错误重定向
[命令] &> [文件]

write by dudu233