1. File Attributes and Access Rights

Every file (or directory) in Unix is associated with several attributes. These attributes help the system—and you—manage and secure files. Key attributes include:

• Inode Number:

  A unique identifier that the filesystem uses internally.

• Type:

  Indicates whether the file is a regular file, directory, special file, or symbolic link. In the output of commands like ls -l, the first character represents the type:

  • `` : Ordinary (regular) file.
  • d : Directory.
  • c : Special character file (e.g., device file).
  • l : Symbolic link.

• Protection Mask (Permissions):

  Specifies who can read, write, or execute the file.

• Number of Links:

  The count of directory entries (names) pointing to the file.

• Owner:

  The user who owns the file.

• Group:

  The group associated with the file.

• Size:

  The size of the file in bytes.

• Date:

  The date of creation or the last modification.

• Location:

  The directory path where the file is stored.

2. Understanding File and Directory Permissions

Unix permissions are divided into three access modes and are set separately for three classes of users.

2.1 Access Modes

• Read (r):

  • For files: Allows viewing or copying the file contents.
  • For directories: Permits listing the contents of the directory (using commands like ls).

• Write (w):

  • For files: Allows modifying, adding to, or deleting the file.
  • For directories: Permits creating, renaming, or deleting files within the directory.Note: Write permission without read permission is often insufficient, as you need to see the directory contents to manage files.

• Execute (x):

  • For files: Allows executing the file if it is a program or script.
  • For directories: Permits accessing the directory (using cd) and, when combined with read permission, listing its content.

• No Permission (-):

  Indicates that a particular operation is not allowed.