LWM-Linux/06 - Linux File Operations/Directories and Symlinks (Shortcuts).md

# Directories and Symlinks

## Directories:

### 1. Definition:
   A directory (also called a folder) is a container in a file system that can hold files and other directories. It organizes files and provides a hierarchical structure.

### 2. Types of directories:
   - Root directory: The top-level directory in the file system hierarchy, typically represented by "/" on Unix-like systems.
   - Home directory: The default directory for a user, usually containing personal files and configurations. "~"
   - Parent directory: The directory one level above the current directory, represented by "..".
   - Current directory: The directory you're currently in, represented by ".".
   - Subdirectory: Any directory contained within another directory. "/usr/bin" - bin is a subdirectory of /usr.

### 3. Directory operations:
   - Create: mkdir (make directory)
   - Delete: rmdir (remove directory - must be empty) or rm -rf ("f"orce remove "r"ecursively, even if not empty)
   - Change: cd (change directory)
   - List contents: ls (list)
   - View path: pwd ("p"rint "w"orking "d"irectory)

### 4. Directory permissions:
   On Unix-like systems, directories have read (r), write (w), and execute (x) permissions. The execute permission allows users to enter the directory.
   - See the section on [Permissions](../05%20-%20Linux%20Permissions%20and%20Ownership/Understanding%20File%20Permissions.md) for examples.

### 5. Hidden directories:
   In Unix-like systems, directories starting with a dot (.) are hidden by default.

## Symlinks (Symbolic Links) or shortcuts (Windows):

### 1. Definition:
   A symlink is a special type of file that points to another file or directory. It's similar to a shortcut in Windows or an alias in macOS.

### 2. Types of symlinks:
   - Soft links (symbolic links): Point to a file or directory by name. They can span file systems and can link to non-existent targets.
   - Hard links: Point directly to the inode of a file. They can't span file systems or link to directories.

### 3. Creating symlinks:
   Use the ln command with the -s option:
   `ln -s target_path link_path` # Create a symbolic link at link_path to the target_path

### 4. Advantages of symlinks:
   - Save space by avoiding duplicate files
   - Create shortcuts to frequently accessed files or directories
   - Maintain multiple versions of files or configurations
   - Facilitate easier software updates and management

### 5. Symlink behavior:
   - When you access a symlink, the system automatically redirects to the target.
   - Deleting a symlink doesn't affect the target file or directory.
   - If the target is deleted, the symlink becomes a "dangling" or "broken" link.

### 6. Identifying symlinks:
   - Use `ls -l` to see detailed file information. Symlinks are indicated by an "l" at the start of the permissions string.
   - The file command can also identify symlinks.

### 7. Following symlinks:
   - Some commands (like cp) don't follow symlinks by default. Use the `-L` or `--follow` options to change this behavior.

### 8. Symlinks in different operating systems:
   - Unix-like systems (Linux, macOS): Native support for symlinks.
   - Windows: Limited support in older versions, full support since Windows Vista.

### 9. Security considerations:
   - Symlinks can potentially be used in symlink attacks, where an attacker creates a link to a sensitive file.
   - Many systems implement symlink protections to mitigate these risks.

### 10. Use cases:
    - Creating shortcuts in the file system
    - Managing shared libraries
    - Facilitating easier software updates