Analysis of the principles and usage of Linux hard links and soft links

In the Linux system, there is a kind of file called link file, which can be used to solve file sharing. There are two types of links: hard link and soft link or symbolic link.

Hard link concept

A hard link (also called a link) is one or more file names of a file.

A hard link is a link made through an index node. In the Linux file system, no matter what type of file is stored in the disk partition, it will be assigned a number, which is called the inode number.

Index) or Inode, which is the unique identifier of a file or directory in a file system. The actual data of the file is placed in the data area (data block), which stores important file parameter information, that is, metadata, such as creation time, modification time, file size, owner, user group, read and write permissions, data block number, etc.

After the hard link is established, the source file and the link file are synchronized, and any modification to either file will be modified

Establishing links can save space. You only need to maintain the link relationship without copying the file.

Soft link concept

A soft link (also called a symbolic link) is similar to a shortcut in the Windows system. Unlike a hard link, a soft link is just an ordinary file, but the data block content is a bit special. The content stored in the file user data block points to the path name of another file. This method can quickly locate the source file entity pointed to by the soft link. Soft links can be created for files or directories.

Soft link function:

• It is convenient for file management, for example, linking a file in a complex path to a simple path for user access.
• Save space to solve the problem of insufficient space. If a file system has run out of space, but now you must create a new directory under the file system and store a large number of files, you can link a directory in another file system with more remaining space to the file system.
• Deleting a soft link does not affect the file it points to, but if the original file it points to is deleted, the related soft link becomes a dead link.

The essential difference between hard links and soft links

A hard link can be considered as a file with two file names; a soft link is a new link file created by the system, which points to the file it refers to.

Limitations of Hard Links

• Soft links can cross file systems; hard links cannot
• A soft link can link to a non-existent file; a hard link cannot
• Soft links can connect directories, but hard links cannot
• Soft links overcome the limitations of hard links. Based on this, focus on soft links. A soft link is also called a symbolic link, which is equivalent to a shortcut in Windows.

Create a soft link

ln -s src_file ln_file

Deleting soft links

rm ln_file

Note: For directory soft leveling

rm ln_dir is to delete the soft link

rm ln_dir/ deletes the files in the directory ln_dir. Of course, the files in the source directory will also be deleted (synchronously).

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