Linux Soft Links and Hard Links

1. Linux Link Concepts Linux links are divided into two types: hard links and symbolic links. By default, the ln command creates hard links.

Hard Links

Hard links connect files via their inode numbers. In the Linux file system, every file stored on a disk partition, regardless of its type, is assigned a unique number called an inode number (Inode Index). In Linux, it is possible for multiple filenames to point to the same inode. This type of connection is generally a hard link. The purpose of hard links is to allow a single file to have multiple valid pathnames, enabling users to create hard links to important files to prevent accidental deletion. As mentioned, this is because the inode corresponding to the directory has more than one link. Deleting just one link does not affect the inode itself or other links. Only when the last link is removed are the file's data blocks and directory entries released. In other words, a file is truly deleted only when all associated hard link files are removed.

Soft Links

Another type of link is called a symbolic link, also known as a soft link. Soft link files are similar to Windows shortcuts. They are actually special files. In a symbolic link, the file is essentially a text file that contains the location information of another file.

2. Deeper Understanding Through Experimentation

[oracle@Linux]touch f1       # Create a test file f1
[oracle@Linux] ln f1 f2      # Create a hard link f2 to f1
[oracle@Linux]ln -s f1 f3    # Create a symbolic link f3 to f1
[oracle@Linux] ls -li        # -i parameter displays inode information

total 0
9797648 -rw-r--r--  2 oracle oinstall 0 Apr 21 08:11 f1
9797648 -rw-r--r--  2 oracle oinstall 0 Apr 21 08:11 f2
9797649 lrwxrwxrwx  1 oracle oinstall 2 Apr 21 08:11 f3 -> f1

From the results above, it can be seen that the hard link file f2 shares the same inode number (9797648) as the original file f1, whereas the symbolic link file f3 has a different inode number.

[oracle@Linux]echo"Iamf1file">>f1
[oracle@Linux] cat f1

I am f1 file

[oracle@Linux]cat f2

I am f1 file

[oracle@Linux] cat f3

I am f1 file

[oracle@Linux]rm -f f1
[oracle@Linux] cat f2

I am f1 file

[oracle@Linux]$ cat f3

cat: f3: No such file or directory

From the tests above, it can be seen that after deleting the original file f1, the hard link f2 remains unaffected, but the symbolic link f3 becomes invalid.

3. Summary Based on this, you can perform some related tests and arrive at the following conclusions: 1). Deleting the symbolic link f3 has no effect on f1 or f2. 2). Deleting the hard link f2 has no effect on f1 or f3. 3). Deleting the original file f1 has no effect on the hard link f2, but causes the symbolic link f3 to become invalid. 4). If both the original file f1 and the hard link f2 are deleted, the entire file will be truly removed.

End.