A file system is a mechanism in a computer's operating system that is used to manage data storage and retrieval. It is responsible for organizing data into files and assigning a unique identifier (i.e., file name) to each file so that users can easily access and manipulate the data. The file system is also responsible for managing the storage space of files, controlling permissions, and providing basic operations such as creating, reading, writing, and deleting files.
1. The basic concept of the file system.
File: A file is a set of data with a specific format, usually used to store different types of information such as text, images, audio, etc. Files can be temporary or durable. Temporary files are created while the program is running and disappear automatically when the program ends;Persistent files remain on disk until manually deleted.
Directories: A directory is a hierarchical way of organizing files into different folders. Each folder can contain other folders and files, forming a tree-like structure. The root directory is the topmost level of the directory structure, and all other folders are directly or indirectly subordinate to the root directory.
Path: A path is a string that represents the location of a file in the directory structure. A path consists of a series of folder names, separated by a slash ( ). For example, a folder named "documents" located in the root directory has the path to "documents".
File name: A file name is a unique name used to identify a file, usually consisting of letters, numbers, and special characters. The filename cannot contain spaces, but can contain underscores ( ) and hyphens (-) The length of the filename varies depending on the operating system and is usually under 255 characters.
II. Components of the file system.
Inode: An inode is a data structure used by the file system to store file metadata, such as file name, size, and creation time. Each file has an inode associated with it, through which the file system can quickly find and access the file.
Superblock: A superblock is the core data structure of a file system, which is used to store basic information about the entire file system, such as total capacity, used space, and free space. Superblocks also contain pointers to the inode area so that you can quickly find the inodes of individual files.
Catalog Items: Catalog items are data structures that describe the files and subdirectories in a directory. Each directory item contains a file name, an inode pointer, and other possible attributes such as permissions, owner, and so on. By traversing catalog items, users can find all the files and subdirectories in the directory.
3. The implementation of the file system.
Sequential file system: Files in a sequential file system are stored in the order in which they appear on disk. This is a simple way to implement, but it is not conducive to efficient random access to files.
Index file system: Files in the index file system are stored in the order in which they are on disk, but each file has an inode associated with it, which is used to record information such as the size and location of the file. This implementation can improve the access speed of large files, but it is less efficient to access small files.
B-tree file system: Files in the B-tree file system are stored on disk according to the B-tree structure, and each node contains multiple pointers to child nodes. This implementation can both improve the speed of access to large files and reduce the cost of accessing small files.
4. Answers to relevant questions.
Q: What are hard links and soft links?A: A hard link is a situation where two or more files share the same node. This means that these files are actually different copies of the same file and their contents are exactly the same. A soft link is a symbolic link from one file to another. A soft link is a shortcut that allows users to access the same object file through different paths.
Q: What is permission control?A: Permission control refers to the process of restricting and managing the user's access to files and directories. Typically, the operating system assigns a unique user ID (UID) to each user and sets a set of permissions for each user. These permissions include basic operations such as read (r), write (w), and perform (x), as well as access to the directory (e.g., listing directory contents, entering the directory, etc.).
Q: What is disk fragmentation?How do I avoid disk fragmentation?A: Disk fragmentation is a situation in which the free space on the disk is spread out into multiple small pieces, resulting in the inability to accommodate a complete new file. To avoid disk fragmentation, you can use the Disk Defragmentation tool to periodically defragment disks to reassemble scattered free space into contiguous areas. In addition, frequent file creation and deletion operations can be minimized to reduce disk fragmentation.