Embedded from entry to mastery (buried) - sharing of ultra detailed knowledge points 3

Linux From entry to mastery （ The grave ）

1. Structure
   a） Concept
   A structure is a type of construction data , Used to describe a message , Or a new data type constructed by an object . The structure makes C Language has the idea of object-oriented .
   b） Format 1
   Struct Structure name
   {
   data type Member variables 1;
   data type Member variables 2;
   ……
   data type Member variables n;
   }
   Be careful ：
2. Visiting members , use . Degraded access .
3. Structural variables can be assigned to each other as a whole , The same members can assign values to each other .
4. When the structure member is impossible, the function , It can be ：
   a） Basic data types .
   b） Other structural variables .
   c） The pointer ： Class A 、 second level 、 A function pointer 、 Array pointer 、 Structure pointer .
   d） Array ： One dimensional array 、 Two dimensional array 、 Function pointer array .
   Structure variable definition format ：
   Struct Structure name Variable name
   Initialization of structure variables
5. First define the structure type , Redefining variables
   a） The definition is not initialized , You need to assign initial values to members one by one .
   b） Direct initialization during definition , The corresponding position sequence assignment .
   c） Dot and wait initialization
6. Define variables as well as structure types （ The structure definition is under the header file ,main On ）
7. and typedef Use a combination of
   a） First define the structure type and then name it .
   b） Rename while defining the structure type , The structure name can be omitted .

c） Format 2：
struct
{
data type Member variables 1;
data type Member variables 2;
……
data type Member variables n;
};

1. Define variables while defining types , Generally, in nested structure types .

2. combination typedef Use .
   d） Structure pointer

3. Define format ：
   Struct Structure name * Pointer variable name ;

4. Access structure members ：
   a）（* Pointer to the variable ） Member variable name ： Take the value of the whole structure variable first , And then use . Demote access members .
   b） Pointer to the variable -> Member variable name ： Direct pointer to the member to access the value of the member .
   e） Array of structs

5. Define format ：
   Struct Structure name Array name [ Subscript ].
   2. Space occupied by structure variables
   The space occupied by a structure variable is the sum of the space opened up by the corresponding types of all members .
   however , There is an alignment rule , Align with the largest space occupied by all member data types to open up memory space .32 The bit operating system is up to 4byte alignment ,64 Bit operating system , The maximum is 8byte alignment .

6. Shared body （ Consortium ）
   a） Concept ： All members share a memory space , Memory opened up by public .
   The size of the space is based on the members that occupy the largest space .
   b） Format
   Union Community name
   {
   data type Member variable name 1;
   data type Member variable name 2;
   ……
   data type Member variable name n;
   };
   Be careful ：

7. When a community is used, the value of a member is used at the same time . That is, initialize the members you want to use

8. The definition format of the common body is similar to that of the structure , Accessing member content also uses . Degraded access .

9. Because the public body shares a memory space , Not very safe . That is, the use of common objects is relatively less . Mainly use the common body to test pc Large and small end .

10. enumeration
    Enum （ Basic variable type ）
    Stm32 linux drive QT in
    #define MON 1
    #define TUES 2
    ……
    #define SUN 7
    Use enumeration types to represent constants
    a） Format
    Enum Enumeration name
    {
    Members of the enumeration 1,
    Members of the enumeration 2,
    ……
    Members of the enumeration n,
    };// Semicolons cannot be omitted
    Generally, enumeration is used to represent some fixed values , such as , It takes only seven days to fix a week .
    Be careful ：

11. Once the enumeration type is defined , The member value in the enumeration determines , Members in an enumeration can only represent an integer , By default, the first member represents an integer 0, The members behind accumulate in turn 1.

12. The members in the enumeration are separated by commas .

13. You can specify an initial value for a member in the enumeration , The member behind a member , Add... To the initial value 1.

14. When the enumeration type is successfully defined , The value of the enumeration member has been determined , You can't change it when you use it next .

15. Generally used in and switch The combination makes the code more intuitive and clear .

16. Linux and unix The difference between
    a） Two big differences

17. Linux It is free software for developing source code , and unix It is a traditional commercial software that protects the intellectual property rights of source code .

18. Unix Most of the systems are matched with hardware , and Linux It can run on a variety of hardware platforms .
    b） redhat and ubuntu The difference between

19. redhat More for servers , Less frequent updates , Stable .

20. ubuntu humanitarianism , Interface optimization is better , Follow xinkuai , Good experience .

21. Linux Architecture
    a） application layer ：app shell
    b） Kernel layer ： Five functions

22. file management

23. Equipment management

24. Network management

25. memory management

26. Process management
    c） Hardware layer ： mouse 、 Keyboard, etc .
    C library ： It provides a set of standard function interfaces for input and output , It can be used on different operating systems . Indirect system call
    system call ： The kernel provides input and output function interfaces up , Based on the kernel , Function interfaces can only be used on this operating system . Different operating systems provide different system call interfaces .

27. Check the operating system version and kernel version

28. see linux Kernel version ：unname -r/-a

29. see ubunt Version of ：lsb_release -a

30. Shut down or restart ：shutdown

31. To turn it off
    a） Shutdown immediately ：sudo shutdown -h now
    b） Timed shutdown ：sudo shutdown -h + Time

32. restart
    a） Restart immediately 1：sudo shutdown -r now
    b） Restart immediately 2：reboot now
    c） Restart regularly ：sudo shutdown -r + Time

33. environment variable

34. Commands for viewing environment variables ：printenv or env

35. PATH： The default search path of the command is saved , The path uses ： separate .

36. If you use your executable program as a command ：
    a） Move the executable program to PATH The variable is saved in the path .
    b） Save the path where the executable exists to PATH In the environment variables .

37. Linux Software installation

38. Understand the types of software packages installed on different systems ：
    System Installation package type
    Windows .exe
    Android .apk
    Ubunt .deb
    Redhead .rpm

39. linux Popular software package management mechanism
    a） debian Linux Put forward ：deb software package
    b） redhead Linux Put forward ：rpm software package

40. deb Classification of software packages
    a） Binary packages ：.deb
    b） Source package ：.dsc

41. Package management tools ：dpkg apt
    Dpkg

42. characteristic ： Installing the software requires that the installation package of the installed software exists , Cannot detect dependencies between software , You cannot get packages from the mirror site , Network is not required for installation .

43. Software
    Warehouse 1（ Address ） Warehouse 2（ network ） Warehouse 3 Warehouse 4
    Baidu （ Source ） Mirror site firefox Google

44. command ：
    a） sudo dpkg -i Complete software name ： Install the software
    b） sudo dpkg -r The software name ： Uninstall software
    c） sudo dpkg -s The software name ： Check the installation status of the software
    d） sudo dpkg -p The software name ： Uninstall completely
    e） sudo dpkg -l The software name ： List the documents of the software

45. Package management tools apt
    Format ：apt- A set of commands ：apt-get、apt-cache
    characteristic ： Installing the software does not require the existence of the software installation package , Can detect dependencies between software , The software package can be obtained from the mirror site , Installation requires network .

46. apt-get command ： install 、 uninstall
    a） sudo apt-get install The software name ： Download the installation software
    b） sudo apt-get remove The software name ： Uninstall software
    c） sudo apt-get download The software name ： Download the package
    d） sudo apt-get source The software name ： Download source package
    e） sudo apt-get updata： Update software source
    f） sudo apt-get upgrade： Update all software
    g） sudo apt-get clean： Clearly download the software package
    h） sudo apt-get check： Check the integrity of dependencies in the system .

47. apt-cache command ： Check the installation status 、 Dependency relationship
    a） sudo apt-cache show The software name ： Get the detailed description of the binary package
    b） sudo apt-cache policy The software name ： Check the installation status
    c） sudo apt-cache depends The software name ： The software I rely on
    d） sudo apt-cache rdepends The software name ： Which software depends on me

48. IP The classification of

49. IPV4 32 position In dotted decimal
    192.168.50.14 C class IPV4 The data before a point is a 8bit( We often use IPV4 C Class is enough )
    IPV4 classification ： Five category
    a） A class ： One byte network number , Three byte host number . The first place is fixed as 0.
    Network segment value range ：0000 0000——0111 1111
    The number of hosts that can be connected to a network segment ：2^24-2
    b） B class ：2 Byte network number ,2 Host number of bytes . First fixed position 10.
    Network segment value range ：1000 0000 0000 0000 -1011 1111 1111 1111
    The number of hosts that can be connected to a network segment ：2^16-2
    c） C class ：3 Byte network number ,1 Byte host number . First fixed position 110.
    The number of hosts that can be connected to a network segment ：2^8-1
    d） Multicast address , First fixed position 1110
    e） Reserved for use , The first place is fixed as 1111.

50. know shell

51. Command line parser

52. Shell Parser version ：sh、csh、ksh、bash

53. Shell、 kernel 、 Hardware 、 The relationship between users ：
    a） The user prompts the terminal to input commands or keys from the command line , Submit to shell
    b） Shell Convert commands to instructions recognized by the bit kernel
    c） The kernel drives the hardware device to realize the corresponding instruction function , Submit the execution results to shell.
    d） Shell Submit the interpretation of the feedback results to the user for identification .

54. shell Basic commands
    a） History query ：history
    b） Command alias ：alias

55. Shell Special characters for

56. wildcard
    a) a）*： Match any length character
    b) b）？： Matches any character
    c) c）[ - ]： Match any character in the range
    d) d）[……]： Match any specified character
    e) e）[^……]： Match any character except the specified character .

57. The Conduit |
    Take one command as input to another .

58. wc command
    a） wc-l file name ： Look at the number of lines in the file
    b） wc-w file name ： Number of words in the file
    c） wc-c file name ： Number of file characters
    d） wc-m file name ： file size

59. grep: Query the string in the file
    grep “ character string ” file name

60. I / O redirection
    a) a）>file: take file Redirect to output source , New mode
    b) b）>>file： take file Redirect to output source , Append mode
    c) c）<file: take file Redirect to input source .
    d) d）2> or &>file: take file File redirection as error message output source .

61. Command substitution character ： stay Esc Under key
    Take the output of one command as an argument to another .

62. Shell Basic system commands

63. man:man man： see man Manual function

64. sudo passwd user name ： Change user password

65. su： Switching users
    a） su： Default switch to root
    b） sudo su user name ： Switch to the specified user
    c） exit： The user who exited the switch

66. data Check the date of the system
    a） sudo data -s year / month / Japan
    b） sudo data -s when ： branch ： second

67. clear Clear the screen

68. df-Th Displays the usage of disk space

69. mount: mount
    How to mount USB disk
    a） Insert the USB drive into the computer and identify it in the virtual machine
    b） adopt df-Th Check the device name and file type of the USB drive
    c） perform sudo mount -t file type Equipment name Mount point
    d） Uninstall method “sudo umount Mount point

70. TFTP、nfs、samba The server
    install TFTP File transfer server ：

71. Check whether the computer is installed
    Sudo dpkg -s tftpd -hpa

72. install
    Sudo apt-get install tftp-hpa

73. It needs to be configured correctly TFTP To ensure normal use
    Sudo vi/etc/default/tftp-hpa

74. establish tftpboot Catalog
    Sudo mkdir /hmoe/tftp
    Sudo chmod 777 /home/tftp

75. start-up tftp service
    Sudo service tftpd-hpa restart

76. Test client program
    Tftp localhost or tftp127.0.0.1（ Native ip Address ）/ The other person's IP Address
    Enter the command ：
    Put a.c// Upload files
    Get a.c// Download the file
    q// sign out
    install nfs service ：

77. Check whether the computer is installed
    Sudo dpkg -s nfs-kernel-server

78. install
    Sudo apt-get install nfs-kernel-server

79. Need modification nfs Configuration file for
    Sudo vi/etc/exports file
    Modified as ：/home/hq/nfs

80. Restart the service ：sudo service nfs-kernel-server restart

81. take /home/hq/nfs The directory is attached to mnt Next （192.168.1.107 When the virtual machine ip）
    Sudo mount-t nfs 192.168.1.107:/home/hq/nfs/mnt

82. uninstall ：sudo umount/mnt
    install samba The server ：

83. Check whether the computer is installed
    Sudo dpkg -s samba

84. install
    Sudo apt-get install samba

85. Need modification nfs Configuration file for
    Sudo vi/etc/samba/smb.conf

86. User management command

87. adduser Create user
    sudo adduser user name

88. usermod Modify or add users
    a） modify ：sudo usermod -l A new user name user name
    b） add to ：sudo usermod -aG user Group

89. Delete user
    Sudo deluser user name

90. Delete the group
    Sudo delgroup Group name

91. Process related commands
    process ： A process is an execution of a program .
    Program ： Executable binary files stored in disk space .

92. File system commands

93. File system type
    a） Disk file system ： Hard disk 、U disc
    b） Network file system ：nfs service 、samba
    c） Virtual file system ：tmpfs
    The format of the file system is ：ext、ext2、ext3、ext4、vfat、fat32

94. file file name ： Check the type of file
    a) a）.elf Executable file type
    b) b）.c
    c) c）.txt

95. rm-f： Mandatory deletion , If the file does not exist, it will be deleted .

96. cat file name ： Output the contents of the file to the terminal .
    Cat-n file name ： Output the file content and line number to the terminal .

97. head file name ： Before the default output file content 10 That's ok
    head-num file name ： Put the file in front of num Output the line content to the terminal .

98. tail file name ： The default output file is the last 10 That's ok
    tail-num file name ： After the file num Output the line content to the terminal .

99. Hard and soft links

100. Hard links ： Through documents inode Link created on . Hard linked files cannot cross file systems .
     command ：in file name Link file name

101. Soft connection ： Links created through absolute paths , As long as you can find the corresponding file in this path , Links work , Equivalent to creating hyperlinks .
     command ：in -s file name Link file name
     characteristic ：

102. If the target file name of the hard link is modified , The link is still valid .

103. If you modify the target file name of the soft link , The connection is broken .

104. Move or delete an existing connection file , May cause link disconnection . If after deleting the target file , Recreate a file with the same name , Soft links will be restored , Hard links are no longer valid , Because the file is inode Has been changed .

105. Decompress and compress

106. gzip and gunzip
     a） characteristic ：

107. Only a single ordinary file can be compressed or decompressed .

108. Cannot archive , The source file does not exist after compression or decompression .

109. After compression, the production compression format is .gz Format .
     b） Compress ：gzip file name
     c） decompression ：gunzip file name .gz

110. Bzip2 and bunzip2（ Features and gzip be similar ）
     a） The compressed format is ：.bz2
     b） Compress ：bzip2 file name
     c） decompression ：bunzip2 file name .bz2

111. zip and unzip
     a） zip function ：zip The command is used to compress one or more files into a single compressed file
     b） zip Format ：zip Compressed file name List of files to compress
     c） unzip function ：unzip The command is used to put zip Decompress the compressed file
     d） unzip Format ：unzip Compressed file to unzip .
     Be careful ：
     a） With archiving function , And compress
     b） You can compress the folder , The suffix is .zip. Compressed folders need to be added -r.
     c） The source file still exists after compression or decompression

112. xz and unxz（ Features and gzip be similar ）
     a） The compressed format is ：.xz form
     b） Compress ：xz file name .xz
     c） decompression ：unxz file name .xz

113. Tar

114. Options ：
     a） -x: Release archive
     b） -c: Create a new archive
     c） -v: Display the process information of archiving and release
     d） -f: The user specifies the file name of the archive file , Otherwise, use the default name , Followed by the filename .
     e） -j: from tar Generate archive , Then from bzip2 Compress
     f） -z: from tar Generate archive , Then from gzip
     g） -J from tar Generate archive , Then from xz Compress

115. Be careful ：
     a） With archiving function , And it can be compressed or decompressed through parameters
     b） The source file exists after compression or decompression
     c） You need to write a fully compressed or decompressed file name

116. Format ：tar Options Compress （ decompression ） file name [ List of files to compress ]

117. Combine ：
     a） -cjf： With bz2 Compressed file in the format of
     b） -czf： With gz Compressed file in the format of
     c） -cJF： With xz Compressed file in the format of
     Be careful ：
     jz stay f front ： The compressed source file still exists
     d）-xvf： Decompress a compressed package ： The compressed package still exists after decompression .

118. Shell Script

119. Essence and characteristics
     a） shell The essence of a script is an ordered set of commands .
     b） shell Script programming is an interpretive language , No compilation required .
     c） shell scripting , It is to realize some functions through certain logical order .
     d） shell The suffix of the script file .sh

120. The steps of writing a script file
     a） Create a script file ：touch xxx.sh
     b） Modify the script file permissions to executable
     Chmod 777 xxx.sh
     c） Edit script content ：vi xxx.sh
     d） Execute script file ：./xxx.sh or bash xxx.sh

121. Shell Variable

122. Allows users to create variables to store data , But it doesn't support data types

123. Format ： Variable name = value （ Be careful ： There can be no spaces on the left and right sides of the equal sign ）

124. Classification of variables
     a） User defined variables
     b） Position variables or command line parameters

125. $0 Executed script

126. $1-$9

127. ${10} - ${N}

128. $# Calculate the number of command line parameters except the execution script file

129. [email protected] $* Traverse all the command line contents except the script file
     c） Predefined variables

130. $? The result of the execution of the previous command 0： really ; Not 0： false .

131. $$ process pid
     d） environment variable

132. Shell The statement in

133. Declarative statements
     a） With # Start to end of the line , Not interpreted to perform
     b） #！/bin/bash Tell the operating system what type of shell Execute this script file .

134. Functional statement ： Any of the shell command 、 User program or other cx

135. Structural statements ： Conditional test statements 、 Multiple branch statement 、 Loop statement 、 Loop control statement .

136. Functional statement

137. read（ similar C Linguistic scanf- Input from terminal ）
     Format ：read var1 var2 var3
     Assign the first word read into the line to var1, The second is assigned to var2, And so on .
     Read-p “ character string ” Variable list ： You can print out strings , And input from the terminal .

138. expr Arithmetic operation command expr It is mainly used for simple integer operation , Include ： Add 、 reduce 、 ride 、 Divide and modulo
     Be careful ：
     a） There must be spaces on the left and right sides of the operator
     b） * and （） You must add an escape character ,*、()
     c） Expr Statement can directly output the operation result

139. let The assignment operation
     a） There must be no spaces in the operation
     b） The result of the operation needs to be assigned to a variable
     c） Variables participate in the operation process without adding $ Value

140. Test sentence ：test Statement can test three objects ： character string 、 Integers 、 File attribute

141. String test
     a） s1=s2 Test whether the contents of two strings are exactly the same
     b） s1!=s2 Test whether the contents of two strings are different
     c） -z s1 test s1 Is the length of the string 0
     d） -n s1 test s1 Whether the length of the string is not 0

142. Integer test
     a） a -eq b test a And b Whether it is equal or not
     b） a -ne b test a And b Is it unequal
     c） a -gt b test a Is it greater than b
     d） a -ge b test a Greater than or equal to b
     e） a -lt b test a Is less than b
     f） a -le b test a Less than or equal to b

143. Testing of file attributes
     a） -d name test name Whether it is a directory
     b） -f name test name Is it a common document
     c） -e name Test whether the file exists

144. Shell Structural statements in

145. if……then……fi sentence
     a） The basic structure ：
     If expression
     Then
     Command table
     Fi
     b） Hierarchical structure ：
     If expression
     Then
     Command table 1
     Else
     Command table 2
     Fi
     c） Nested structure ：
     If expression
     Then
     Command table 1
     Else
     If expression
     Then
     Command table
     Fi
     Fi
     d） elif
     if expression 1
     then
     Command table 1
     Elif expression 2
     Then
     Command table 2
     Elif expression 3
     Then
     Command table 3
     ……
     Else
     Command table n
     Fi
     Be careful ： If the expression is true , Execute the commands in the command table ; Otherwise quit if sentence , The perform fi Subsequent statements .
     if and fi Is a statement bracket for a conditional statement , Must be used in pairs ; The command in the command table can be a , It can also be several .

146. case sentence
     Format ：
     Case String variable in
     Pattern 1）
     Command table 1
     ;;
     Pattern 2）
     Command table 2
     ;;
     ……
     Pattern n）
     Command table n
     ;;
     Esac
     Be careful ：
     a） case Statement can only detect string variables
     b） The command table ends with a single double quotation line , sign out case sentence
     c） Pattern n Often written as characters * Represents all other modes
     d） Case There can be multiple patterns in the match , Between each mode | separate .

147. For……do……done Circular format ：
     For Variable name in Word list
     Do
     Command table
     Done
     Be careful ：

148. The variable takes each word in the word list in turn , Every time you take a word , Just do it once .

149. Commands in the loop body , The number of cycles is determined by the number of words in the word list .

150. The command in the command table can be a , It can also be multiple lines separated by semicolons or line breaks .
     For Several writing formats of sentences

151. for I in 1 2 3 4 do……done： Variable i Take values from the word list

152. for I do……done Variable i Take values from the command line , It can be omitted in Word list

153. for I in{1…10} do……done： Variable i from 1-10 Take value from the number

154. for（（i=0;i<10;i++）） do……done The writing format is similar to C Language

155. While loop
     Format ：
     While Command or expression
     Do
     Command table
     Done
     Be careful ：while Statement first tests the value of a subsequent command or expression , If it is true , Just execute the command in the loop body once , Then test the value of the command or expression , Execution loop body , Exit the loop until the command or expression is false .

156. Until loop
     Format ：
     Until Command or expression
     Do
     Command table
     Done
     Be careful ：until Circulation and while The function of the loop is similar , The difference is that only when the value of the tested command or expression is false , To execute the command table in the loop body , Otherwise exit the loop , This is related to while The order is just the opposite .

157. Loop control statement ：break And continue
     Break： End this cycle
     Break n： Jump out of n Once circulates
     Continue： End this cycle and continue the next cycle
     Continue n： Go to recent n Once on the next round of the loop statement .

158. Shell Array

159. Array definition and initialization
     a） arr=(v1 v2 v3 v4)
     b） arr=($1 $2 $3 $4)c）readabcarr=($a $b $c)
     d） read -a Array name

160. Access array
     a） Take an element of the array ：$CountGroupname[Nextmark]0b）YesCountGroupelementplainOfvalueInto\; theThat\text{'}s\; okrepairChange：CountGroupname[Nextmark]=valuec）All\; overcalendarCountGroup：${ Array name [@]}
     d） Get the number of array elements ：${# Array name [@]}