Linux common commands (i)

1. The Library file on window is a. dll format, and the library file on Linux is. So

2. Computer architecture

computer Underlying hardware resources : is completely independent, used to perform operations on the upper data

kernel kernel: as a middle layer, let the upper layer program transparent to the underlying hardware requirements, the upper layer through the kernel calls the underlying hardware, this is what we call the system calls, but the system call is too low, as you need to buy steamed bread, the system call to you a bunch of wheat, So the system calls the program to do a lot of things, but the system call is absolutely the highest authority, or the closest to the bottom, hackers can hack into a system of the kernel is very dangerous.

Library API: A lot of packaged software to make the upper program call the hardware directly. Like the kernel gives you the wheat, you can make the head, dumplings, buns, etc., according to your upper program requirements directly with the Library API software interface.

the upper level of the various programs: such as Shell, Word, PPT .....

3. If you develop an operating system, it is necessary that the hardware, the kernel, the shell and the shell to do the necessary library, can be made into a simple operating system, but the system is no other function.

4. Authentication at Linux Login

Login: User name (User ID)

Aaa:authentication (authentication), Authorization (authorization), Audition (audit, generally via logging)

5. Magic Number (Magic): The execution of the program entrance, in front of the program of the binary special characters, such as when we write the program will be written in front of the #! /bin/bash, this is the program execution portal, which is the magic number

6. List:ls---- lists, lists the files under the specified path (displays files in the current directory)

Directory: Also a file, is a path mapping

Many options:

-L: Displays many properties of a file, called Long format

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The first identifies a different identity, as follows

-: Normal file (f)

D: Catalog file

B: Block device files (blocks)

C: Character device file (character)

L: Symbolic Link files (symbolic link file)

P: Command pipe file (pipe)

S: Socket file (socket)

The following 9-bit, three-bit group, no use-representation, rwx (read-write-execute)

Number of hard links to files

Owner of the file

Genus Group of files

Size of the file (size), in bytes

Time stamp (timestamp), last modified time, last visited time, last changed time. (The modification is to indicate that the contents of the file are modified, and the properties of the file are changed)

-H: Do unit conversions

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-A: Show hidden files, hide files with "." Begins with

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. Represents a hidden file for the current directory

.. Represents the parent directory

-A: Displays hidden files for the current directory and does not show hidden files from the parent directory

-D: Display the directory's own properties

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-R: Show files in reverse order

-R: Recursive display of files (that is, all folders in the file are shown to you)

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7. PWD: Shows what the current directory is. Top-level catalogs are generally denoted by "/"

8. Index node: Each file in the Linux system has its own unique numeric number, which can be viewed by the following command

-I: Displays the unique inode number of the file

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9. Switch directories with Cd:change directory, only the name of the directory behind the CD

The CD is not followed by any parameters, which means switching to the home directory or calling home directory

CD ~ User name, enter the home directory of the specified user, only the administrator has permission to enter

CD-can switch between the current directory and the present directory

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Types of Linux commands:

Built-in commands (shell built-in)

External command: There is an executable file corresponding to the command name under a path in the file system

You can display the type of file that the command belongs to in type

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11. What is an environment variable?

Named memory space is called a variable, variable assignment, such as Name= "atom"

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Hash: You can see how many times the command you used was hit, the first executed command went back to look up, and the same commands that followed were extracted from the cache. The cache container is the hash value of the command, much faster than you are going to fetch the data directly.

Path: Use colon-delimited paths. is an environment variable. If a new program command must be placed in a path path, it cannot be executed.

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Linux common commands (i)