[Bird Brother Linux Video tutorial finishing]02_01_linux operating system and common commands

First, the operating system structure:

First, the lowest layer is the hardware, on a single CPU system platform, the hardware resources are independent. In order to be able to run multiple software simultaneously on the same computer, so the common management software called the kernel (kernel), the kernel is just a platform, it does not provide any specific task, just the hardware has the computing power to be abstracted out and provided to the upper layer of other software, The way it is provided is called system call. Because system calls are too low-level, it is cumbersome for programmers to use system calls to develop programs, so with libraries (Library:api-application program Interface), A library is the ability to encapsulate one or more system calls into a more advanced calling interface. A library is an executable program, but cannot be executed independently and must be called before it can be executed. The library referred to here is usually called a shared library or a dynamic shared library. At the top of the library are various applications such as shells, Web servers, KDE, Ides, and so on.

650) this.width=650; "Src=" Http://s1.51cto.com/wyfs02/M01/8A/E2/wKioL1g-g2zgMMZcAAIQC9-z4uI173.png-wh_500x0-wm_3 -wmp_4-s_2236554793.png "title=" 111.png "alt=" Wkiol1g-g2zgmmzcaaiqc9-z4ui173.png-wh_50 "/>

Second, the system login:

1.login: User ID

1. Authentication mechanism: Authentication

2. Authorization: Authorization

3. Audit: Audition (log)

2. Command prompt:

A command can be either a binary or a script file, which is strictly distinguishable from two different types for the kernel. Typically an executable file must have a program's execution entry. So at the beginning of the binary file there is a special character or a unique number of bytes marked, we call it magic numbers, magic number can be labeled Binary program execution format. The magic number of programs executed on Windows and Linux is different, and the binary format they understand is not the same, so even if the libraries are identical, the libraries compiled on Windows will not necessarily be able to run on Linux systems.

Iii. Common commands:

Catalog: Working directory, current directory

file, Path mapping

Path: The location that passes from the specified starting point to the destination

FileSystem: File System (hierarchical file management mechanism)

1.ls:list List-Lists files under the specified path

-L: Long format displays full information about the file

1). File type:

-: Normal file

D: Catalog file

B: Block device files (blocks)

C: Character device file (charcter)

L: Symbolic Link files (symbolic link file)

P: Command pipe file (pipe)

s: Socket file (Socket)

2). File permissions: 9-bit, every 3-bit group, each group: rwx (Read, write, execute)

3). Number of hard links to files

4). Owner of the file

5). Genus Group of files

6). File size (size), Unit bytes

7). Timestamp (timestamp)--the time of the most recent modification

Access: Access

Modified: modify--file content has changed

Change: change,matedata, meta data

-H: Do unit conversions (K)

-A: Show hidden files starting with.

.: Current Directory

..: Indicates parent directory

-A: not shown. and.

-D: Display the directory's own properties

-i:index node,inode Display file miniature node number

-R: Reverse Display

-R: Recursive display (recursive) fairly occupies system resources

2.pwd:printing working Directory

3.cd:change Directory

Home directory, home directory, home dirctory

CD ~username: Access to the specified user's home directory, only administrator privileges to use

CD-: Switch back and forth between the current directory and the previous directory

4.type: Shows what type of command it belongs to

Command type:

Built-in command: Shell (built-in) builtin

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

Environment variables: named memory space

5.PRINTENV: Display Environment

Path: Paths separated by colons

6.hash: Cache-Enables system acceleration

A hash is a key value segment (key value) or a key-value database, where the speed of finding content in a key-value library is 0 (1), and O (1) is the standard for measuring a program's execution speed.

O (1): Find the speed of a data from a list the ratio of changes in the length of the list or the trend of a function, the large O-ID, no matter how long the queue is, the time it takes to find the content is the same.

This article is from the "Linux Blind Advanced Road" blog, please be sure to keep this source http://blindbird.blog.51cto.com/12338383/1878239

[Bird Brother Linux Video tutorial organizing]02_01_linux operating system and common commands