What is the difference between hard link and symbolic link in Linux?

Hard Link vs. Symbolic Link in Linux

In the Linux file system, there are two types of links: hard links and symbolic (soft) links. Both serve the purpose of creating a reference to a file, but they differ in their implementation and behavior.

Hard Links

A hard link is a direct reference to the actual file data on the disk. When you create a hard link, it points directly to the inode (index node) of the file, which contains the metadata and the location of the file data on the disk. This means that the file data is shared between the original file and the hard link.

Characteristics of Hard Links:

1. File Data Sharing: Hard links share the same file data, which means that any changes made to the file content through either the original file or the hard link will be reflected in both.
2. Inode Sharing: Hard links point to the same inode, which means they share the same file metadata, such as permissions, ownership, and timestamps.
3. Deletion Behavior: Deleting the original file or a hard link does not affect the other links. The file data will only be deleted when the last hard link is removed.
4. Limitations: Hard links cannot be created across file system boundaries, and they cannot be created for directories.

Example:

# Create an original file
touch original_file.txt

# Create a hard link
ln original_file.txt hard_link.txt

# Verify the hard link
ls -l
# Output:
# -rw-r--r-- 2 user group 0 Apr 24 12:34 original_file.txt
# -rw-r--r-- 2 user group 0 Apr 24 12:34 hard_link.txt

In this example, hard_link.txt is a hard link to original_file.txt, and they share the same inode and file data.

Symbolic (Soft) Links

A symbolic link, also known as a symlink, is a special type of file that contains a reference to another file or directory. Unlike a hard link, a symbolic link does not point directly to the file data; instead, it contains the path to the target file or directory.

Characteristics of Symbolic Links:

1. Target File Reference: Symbolic links contain the path to the target file or directory, which can be absolute or relative.
2. Independent File Data: Symbolic links do not share the file data with the target file. They are independent files with their own metadata.
3. Deletion Behavior: Deleting the symbolic link does not affect the target file, but deleting the target file will break the symbolic link.
4. Cross-File System Boundaries: Symbolic links can be created across file system boundaries, unlike hard links.
5. Directory Support: Symbolic links can be created for directories, unlike hard links.

Example:

# Create an original file
touch original_file.txt

# Create a symbolic link
ln -s original_file.txt symlink.txt

# Verify the symbolic link
ls -l
# Output:
# -rw-r--r-- 1 user group 0 Apr 24 12:34 original_file.txt
# lrwxrwxrwx 1 user group 9 Apr 24 12:34 symlink.txt -> original_file.txt

In this example, symlink.txt is a symbolic link that points to original_file.txt. The symbolic link has its own metadata, and it does not share the file data with the original file.

In summary, the main differences between hard links and symbolic links in Linux are:

1. File Data Sharing: Hard links share the same file data, while symbolic links do not.
2. Inode Sharing: Hard links share the same inode, while symbolic links have their own independent metadata.
3. Deletion Behavior: Deleting a hard link does not affect the file data, while deleting a symbolic link breaks the reference to the target file.
4. Cross-File System Boundaries: Symbolic links can be created across file system boundaries, while hard links cannot.
5. Directory Support: Symbolic links can be created for directories, while hard links cannot.

The choice between using hard links or symbolic links depends on the specific use case and the desired behavior. Hard links are useful when you want to create multiple references to the same file data, while symbolic links are more flexible and can be used to create references across file system boundaries or for directories.