Linux Basic-----File system

File system: Manage files to achieve file name access:
Rootfs: Root file system
Leaf node: file (the last level to be unable to store other files)

The file system is provided by the kernel and the data is stored on the hard disk, and the program does not communicate directly with the hardware, initiating the request to the kernel via the kernel-provided interface (System call)
The kernel does the work, but the system calls are too low, and multiple system calls are encapsulated into more advanced interfaces to provide upper-level application use, these packages

After the system calls the library (API), through the library to use some features, such as read write execution delete calls.


MBR: Total 512 bytes (0 sectors of hard disk) boot the operating system on the entire disk
446 bytes: bootloader
64 bytes: Partition table
2 bytes: Whether the disk is bootable

Each partition first two sectors (1024 bytes) boot block: Boot blocks: Used to boot the operating system on the partition

The filesystem will be partitioned into 3 parts, the Boot block index store, and the storage zoning divided into blocks, 1K 2K 4 K, the file system will give
These blocks are numbered (block numbers) and are based on the corresponding relationships within the index to determine which blocks the data is stored in.

Index information (metadata): File size permission is the label of the block corresponding to the time stamp data of the main group (disk block pointer implementation)

Disk Block pointers: If the data is too large to occupy chunks, and the data block label information stored in the inode, resulting in indoe is too large, in order to solve this problem, the use of hierarchical structure:

If it is a small file, the disk block pointer will directly point to the data block (direct pointer), if the file is too large, using a level two pointer to a region, the area indicates that this is an area, this area contains a portion of the disk block designator information, thus saving indoe space

Each file will have an entry, each of which is referred to as: Index node
The entire space is called an index, and each entry is called an index node: inode: File metadata: Not related to data content
For easy lookup, each inode has a number: Inode number

Directory: Path mapping of files: Directories are also files, there are indoe entries, and data is stored on hard disk blocks
Directory disk block data: The type of file name file that corresponds to the indoe number of files in this directory

The directory contains only the first-level subdirectory information in the directory, does not contain the file information in subdirectories, and the file information in subdirectories is stored in subdirectories.

If there is a log directory below/Var, var only need to log the log information, and log the following file information, there is a log record)

Such as: How file system find/var/log/messages this file
1. First, according to the inode number of the root (root will be self-reference), find the root of the inode, through the inode to find the corresponding disk block, this disk block contains var This file's inode number and corresponding file name and type,
2. Through the Var inode number, to find the corresponding indoe, through the Var inode information to find the disk block var this file, through the disk block data to find the log directory inode number and the corresponding file name and type of files
3. Through the inode number of log, find the log indoe to determine the disk block, through the disk block stored in the memssages the file's inode number and corresponding file name, determine which disk block, and finally read the contents of messages

Create a file

1. Find an idle Iode, free disk block

Inode bitmap: One bit for each inode, 0 for idle, 1 for occupancy

Block Inode bitmap: One bit for each block, 0 idle, 1 occupied

Block group: Blocks (the number of blocks in the group is equal)

By dividing too many blocks into different groups, when looking for an idle inode or block, you can scan a set of bitmaps, determine the idle according to the bitmap, and if a group is not enough, you can reference it across groups

Each group is self-managing

The 2nd 1024 byte of the disk is called: Super Block (block Group 0 Super Block)

Super BLOCK: Stores how many groups are on the disk, from which block to the end of each group

GDT: Block Group Description Table: where the block bitmap holds the Inode graph where the inode table holds the free block idle Inode

Each block group has its own: Inode table block bitmap inode bitmap GDT

Tune2fs-l: View Super Block

F

DUMPE2FS: Output ext File System Information

-H: Show Super Block information

Du directory: View the file size and total size of the directory

-S: View only the directory size
-H: Unit conversion, show the more intuitive way

DF: Display disk-related information

-L: Disk information Total capacity block with block idle block using proportional mount point

-H: humanized display

-p:posix-compatible style display

-i:indoe Related Information

Delete

1. Clear the Inode data for the file. Categorize inode to unused

2. The block data is not cleared by default, only the disk block is classified as unused, and if used in the future, directly overwrite

Copy

1. Find free blocks to copy the data into and create a new inode

Move (same partition)

1. Create an entry in the new path that points to the original inode

2. Delete the corresponding entry of the original path, the inode of the file and the database is not moved

Move (not a partition)

1. Create a new file, delete old files

Link files ln-s original file link file

Soft Connect (symbolic Link)

Ls-l file Link file type L

Whether the test file is a soft connection file in bash

1. Can cross-partition, can be created for all files, including directory

2. Delete the original file, the linked file will not be used

3. All linked files, with the original file pointing to different inode, not the same file

Hard Link ln Original file link file

1. Two different paths point to the same inode, using the same disk block

2. Delete a path, not the inode of the file, know the last path on the file to delete

3. Hard connections cannot span partitions and cannot establish hard connections to directories

Ls-l 2nd column shows the number of times the file was hard connected

Ls-i displaying the inode of a file

4. All connections point to the same inode, so they are the same file

Ext System File System: Extended Properties

Lsattr Show Extended Properties

Chattr Modifying Extended Properties

-A: Only append content is allowed

-I: becomes a read-only file for everyone, including root

Compressed Decompression Archive

Compression: TAR-CZVF test.tar.gz/test

-C: Create compression

-Z: Using gzip compression

Zip format zip test.zip test

Zip Format decompression Uzip test.zip

Decompression: TAR-XVF test.tar.gz

-C: Specify the decompression path

DD command

DD if= Original file of= target file

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