Linux Basics (1-10)

1. Help commands

man 命令
/【要搜索的内容】

The level of man

1 Help for viewing commands
2 viewing Help for functions that can be called by the kernel
3 Viewing the Help for functions and function libraries
4 view Help for special files (mostly files in the/dev directory)
5 Viewing the Help for a configuration file
6 Viewing the game's help
7 See other miscellaneous Help
8 viewing Help for commands available to system administrators
9 viewing and kernel-related files Help

See what level of Help the command has

man -f 命令Equivalent towhatis 命令
For example man -f passwd , you will see the passwd command has a configuration file, so man 5 passwd you can see the configuration file with Help, whereis passwd you can see the location of the file

View all commands that contain keywords

man -k 关键字Equal to apropos 关键字 , as inapropos passwd

2. Aliases and shortcut key viewing and setting aliases

aliasView all command aliases in the system
alias 别名=‘原命令‘To set the alias of a command
such as alias rm=‘rm -i‘ oralias ll=‘ls -l‘
It's equivalent to setting up a shortcut command, but it's temporarily in effect

Aliases are permanently active and delete aliases

vi ~/.bashrcWrite environment variable configuration file
unaliasTemporarily remove aliases

Common shortcut keys

shortcut Keys	meaning
ctrl+c	Force the current command to terminate
ctrl+l	Clear Screen
ctrl+a	Cursor moves to the beginning of the command
ctrl+e	Cursor moves to the end of the command line
ctrl+u	Delete the cursor at the beginning of the row
ctrl+z	Put the command in the background
ctrl+r	Search in the history command

3. Common Directory Role

/root directory
/bincommand to save the directory (normal user can read the command)
/sbin
/usrSystem Software Resources Directory
/bootStart directory, start related files
/devDevice File Save Directory
/etcConfiguration File Save Directory
/libsystem function Library Save directory
/mntSystem Mount Directory
/mediaMount Directory
/sys/procSave Memory mount point, cannot be manipulated directly
/tmpTemp directory, storing temporary data
/varSave system Variable Document directory

/usrUnder the /bin /sbin same directory, the same as / the two directories to save the system command, the /sbin next command only Superuser can execute
You can leave the contents of the home directory, or the root directory / , as well as the /tmp directory under the content, others do not move, but also do not recommend in the root directory, only to put the necessary data

4. Mount commands

Equivalent to the allocation letter in win, except that Linux is called mount

Query and Auto Mount

mountQuerying devices that are already mounted in the system

• ~ on ~ type ~This is the structure of the show.
• Such as/dev/sda5 on / type ext4 (rw)
  Which sda5 represents the first SATA hard disk fifth partition, / which represents this is the root partition, ext4 representing the file system is EXT4, permission is read and write;
• Similarly, the /dev/sda1 on /boot type ext4 (rw) first partition that represents the first SATA hard drive is the boot partition, the file system is EXT4, and the permissions are read-write

mount -aAccording to the contents of the configuration file /etc/fstab , all the devices written in this file are mounted once, such as /，/boot，/home，swap these partitions are in the file, so the system will automatically mount these partitions at each boot

Mount command format

mount【-t文件系统】【-o特殊选项】设备文件名 挂载点
-t 文件系统Add the file system type to specify the type of mount, you can ext3,ext4,iso9660 the file system
-o 特殊选项Additional options for mounting can be specified, with various parameters, can be multiple together, separated by commas
Special look at this exec/noexec , on behalf of the execution/not execution, set whether to allow executable files in the file system, the default is the exec file
For example, to mount -o remount,noexec /home/ re-mount /home the partition, and do not allow executable files, at this time if you go again ./hello.sh will show insufficient permissions

5. Shutdown and restart command shutdown command

shutdown 【选项】时间
-cCancels the previous shutdown command
-hShutdown
-rRestart

• Use the date command to see the system date
• shutdown -r 05:30Indicates a restart at 5:30 A.M., this time into the countdown state, can no longer operate, by ctrl+c canceling.
• At the end of the add & , so that the command in the background, do not occupy the operation interface, two times after the return to continue their operations. If you do not want to execute this command in the background, you can use it shutdown -c to cancel.
• shutdown -r nowIndicates a reboot now.
• Avoid using this command when you telnet to the server!

Other shutdown commands

halt
poweroff
init 0
But none of these three are safe.

Other Restart commands

rebootMore secure
init 6Not safe

What do the 0 and 6 here mean?

Represents seven levels of system operation
0 Turn off the machine
1 single user, can be regarded as the safe mode in win, used for system repair
2 not fully multi-user, without NFS service (file sharing service)
3 full multi-user, is the black-bottom white character interface
4 Not assigned
5 graphical interface
6 restart
Init means calling a level
Use runlevel to see exactly at what level the system is running, MAC OS does not support
cat /etc/inittabChange the system boot default level by locating the fields in the file id:3:initdefault and modifying the numbers. But it must not be set to 0 and 6.

Exit Login Command

logout

6. Pipeline than characters command sequence execution

Multi-Command executor	format	function
;	Command 1; Command 2	Multiple command order execution, no logical connection between commands
&&	Command 1 && Command 2	Logical AND, command 1 executes correctly only if command 2 is executed, command 1 does not execute correctly, and command 2 does not execute
Shift+\shift+\	Command 1 shift+\shift+\ Command 2	Logical OR, command 2 does not execute when command 1 is executed correctly, and command 2 does not execute when command 1 is executed correctly

* Which shift+\ means that|
For example, date ; tar -zcvf etc.tar.gz /etc ; date you can calculate the time-consuming execution of intermediate packed compression commands
Again, the ls && echo yes || echo no first command executes correctly, output Yes, error execution, output no

Pipe character

Command format: 命令1 | 命令2 , there is a certain programming idea inside the command 1 the correct output as the operand of command 2, and the logic is not the same as
Example:

• ls -l /etc | moreRepresents ls -l /etc the output split-screen display
• netstat -an | grep ESTABLISHEDRepresents netstat -an a row with established in the search output
  If it becomes again netstat -an | grep ESTABLISHED | wc -l , this is a multi-pipe character command, representing the number of rows with established to the last statistic, you can see how many people are connected on the server
• If cat there is a lot of repetition in the content of the output, you can add it to the back |uniq

7. How the script executes the echo output command

echo【选项】【输出内容】
echo "cangls he bols ni xi huan na yi ge?"double quotes are required as long as there are spaces in the output
Option -e to indicate support for antisense characters

Echo can support the antisense character (also can be used in Python)

anti-semantic characters	function
\a	Output warning tone
\b	Backspace key, that is, delete key to the left
\ n	Line break
\ r	Enter
\ t	tab, which is the TAB key
\v	Vertical tab
\0nnn	Output characters according to the Octal Ascⅱ code table. Where 0 is a digital zero and NNN is a three-bit octal number
\xhh	Output characters according to the hexadecimal Ascⅱ code table. Where HH is a two-digit hexadecimal number

For example echo -e "\x68\x65\x6c\x6c\x6f" , to manually enter a hexadecimal Ascⅱ code value for a character, the output ishello
The pure character interface of Linux native is not supported in Chinese!
In addition, in the remote tool interface such as Xshell can support the color display, such as echo -e "\e[1;31m 嫁人就要嫁凤姐 \e[0m" , which \e[1;31m is the open color, \e[0m is the turn off color, 31m indicating red, can support the color from 30 to 37

First script

vim hello.sh#!/bin/bash#注释echo -e "\e[1;34m 天上掉下个林妹妹 \e[0m"

Script execution

• Give execute permission, invoke script
  chmod 755 hello.sh
./hello/sh#相对路径
• Execute scripts directly from bash
  bash hello.sh

8. Historical Command History command

history 【选项】【历史命令保存文件】
Options:
-cClear History Command
-wWrite the history command in the cache to the history command to save the file~/.bash_history
The history command saves 1000 by default and can be modified in the environment variable configuration file /etc/profileHISTSIZE=1000

Invocation of the history command

• Use 上下箭头 to invoke previous history commands
• Using the !n repeat nth command
• Use !! repeat to execute previous command
• Use !字串 repeat to execute the last command that starts with the string

Command and file completion

In bash, command and file completion are very handy and common functions we just press the Tab key to automatically complete the command or file when we enter it.

9. Link Command Link command

ln -s 【原文件】【目标目录】
function is to generate a linked file
-sCreate a soft link

Features of hard links

1. Hard links have the same I node and storage block blocks, which can be seen as the same file
2. Can be identified by the I node
3. Cannot span partitions
4. Cannot use for directory

ln desktop/Learning_Python/hello_world.py documents/hello_world.hardls -l desktop/Learning_Python/hello_world.py-rw-r--r--  2 Jeff  staff  3379  3 14 10:30 desktop/Learning_Python/hello_world.pyls -l documents/hello_world.hard-rw-r--r--  2 Jeff  staff  3379  3 14 10:30 documents/hello_world.hardls -i desktop/Learning_Python/hello_world.py documents/hello_world.hard2231081 desktop/Learning_Python/hello_world.py2231081 documents/hello_world.hard

Features of soft links

1. Similar to win under the shortcut
2. The soft link has its own I node and block blocks, but the data block only saves the original file name and I node number, and there is no actual file data
3. IrwxrwxrwxIthe permissions for soft link soft link files arerwxrwxrwx
4. Modify any file and the other changes
5. Delete original file, soft link cannot be used

10. Command format

[root@localhost ~]#

rootSegment represents the current user, localhost is the host name
If it is a superuser, the current directory is the /root root directory, and if it is a normal user user1, the/home/user1
#Represents the current user bit super user, $ or normal user

Format:命令 【选项】【参数】

Query Directory Contents command

ls 【选项】【目录/文件】

ls -l ~/desktop[email protected]  3 Jeff  staff    102  3  8 11:08 $RECYCLE.BINdrwxr-xr-x   6 Jeff  staff    204  4  9 16:13 A*算法drwxr-xr-x  10 Jeff  staff    340  4  9 16:14 Learning_Python-rw-r--r--   1 Jeff  staff   1441  3 30 11:43 SSH设置-rw-r[email protected]  1 Jeff  staff  48640  3  8 11:08 Thumbs.dbdrwxr-xr-x  10 Jeff  staff    340  4  9 18:07 myBooksdrwxr-xr-x  10 Jeff  staff    340  4 10 11:02 毕业规范-rw-r[email protected]  1 Jeff  staff   6313  4  8 21:36 实习小结.md

-lShow more information
Permissions 10-bit-rw-r—r—
The 1th digit represents the file type:-file d directory l soft link file
rw-U owner Class
r--G belongs to group Meimei
r--O Other people's deputies, silly monks.
rRead and w write x execution
3,6,10 These numbers represent reference counts
102,204,340 These numbers represent the size of the bytes and are converted to ls -lh KB for easy reading

ls -a ~/desktop$RECYCLE.BIN.DS_StoreLearning_PythonmyBooks..localizedSSH设置毕业规范..A*算法Thumbs.db实习小结.md

-aShow all files, including hidden files
-laShow all files in detail

ls -ld ~/desktopdrwx------+ 12 Jeff  staff  408  4 10 17:07 /Users/Jeff/desktop

-dShow Directory Properties
-ldShow directory properties in detail

If the directory does not have W permissions, even if the file has write permissions, you can not move the file, rename the operation, at this time, you need to add the directory W permissions: chmod +w (note that the CWD is this directory)

Linux Basics (1-10)