Linux-System file Structure

File system architecture for Linux systems

/: Starting point of the file system structure
/home: Household Directory
/bin: Standard directives and tool programs
/usr: System uses files and instructions
/usr/bin: User commands and tool programs
/usr/sbin: System administrator Command
/usr/lib: Programming Language Library
/usr/doc:linux Documentation
/usr/man: Online Help manual
/usr/spool: Spool Files
/sbin: Administrator's command to turn on the system
/var: time-varying files, such as mailbox files
/dev: Device File interface
/etc: System configuration files and other system files

The concept of file systems

File system: A region of a specific format on a disk
File: A named object that stores data in a file system
Directory: A special type of file that contains many file items
Subdirectories: Directories that are contained in another directory, directories that contain subdirectories are called parent directories
File name: A string used to identify files, saved in a directory file entry
Path name: A collection of one or more file names that are combined with the "/" character. It specifies the location of a file in the file system
File structure: Regardless of whether a file is a program, a document, a database, or a directory, the operating system assigns it the following structure
Index node (i node)
Contains a record of the corresponding file information (file permissions, file master, file size, and so on)
Data
The actual contents of the file

File type

Normal file: string with various lengths
Text file: composed of ASCII characters
Data files: composed of digital and text-based data from applications such as spreadsheets, databases, etc.
Executable binaries: composed of machine instructions and data
Directory files: Composed of paired "I-node/filename"
The I node number is the index that retrieves the table of the I node, and the I node holds the status information for all the files.
A file name is a string of text in the form of an assignment to identify a file
Device file:/dev/tty1
Connection file: The path to a file in the FileSystem file file name

User Login System

After the system starts, enter the user name and type enter key. Such as:
Login:root
Enter the user password and the password you entered will not be displayed on the screen. If you enter a wrong password, the screen prompts the following information:
Login Incorrect
Login
After you perform these two steps, if the screen displays a system prompt, such as:
[[email protected] root] #
Instructions have been successfully logged on to the system and can be manipulated

Remote Login System

User Telnet cluster
Ordinary users through Telnet from the outside of the cluster to log on to the cluster node, the first to establish an account through the cluster system administrator
Administrator Login via Rlogin
via SSH command
Inside the cluster
Because each ordinary user account is a global NFS account, it can be accessed through rsh within the cluster
Example
Telnet VIP (VIP for the cluster system external IP address, set by the user IP)
Login:team01
Password: * *
RSH node161 (Access other nodes inside the cluster via rsh, node161 the host name of the node within the cluster)

Exit system

After the user uses the Linux system, the process of exiting the system is called "logoff"
There are three different methods
Type: Exit
Press: Ctrl+d (equivalent to execute exit)
Logout

Shutting down the system

The shutdown command must be typed by the root user at the shell prompt
The system will complete shutting down all processes
Freeing up resources to stop running
Power off
command to shut down the system
[[email protected]/root] # shutdown–h now
[[email protected]/root] # halt
[[email protected]/root] # init 0
[[email protected]/root] # Poweroff
Rebooting the system
Reboot command
Shutdown-r Command
Combo Key Ctrl+alt+del (only available under console)
Shutdown command
Syntax: Shutdown [flag] [warning message]
Flag
-R Restart
-H shutdown
-K does not shut down and only sends messages
Time
Absolute time: hh:mm
Relative Time: +mm (min)
Immediate shutdown: Now (=+0)
Linux system has a disk buffer
This buffer does not immediately write all the data to the disk.
Instead, the data is written to disk after a period of time
Turning the power off may cause the cache to not write back and the file system on the disk is incomplete
Multi-tasking system for Linux
There may be many programs that are running in the background
Only through proper shutdown sequence can we ensure that all background processes can save their own data.

Linux-System file Structure