File Attributes - aryanjoshi0823/5143-Operating-System GitHub Wiki

File attributes are metadata associated with a file in a file system. These attributes provide information about the file's properties, such as permissions, size, timestamps, and access rights.

Key File Attributes

  1. Name

    • The identifier of the file (e.g., example.txt).
    • Unique within its directory.

  2. Type

    • Indicates the nature of the file:
      • Regular file (text, binary, executable, etc.)
      • Directory
      • Special file (e.g., device files in Unix/Linux)

  3. Location

    • The physical or logical address of the file on the storage device.
    • Managed by the file system.

  4. Size

    • The total amount of space (in bytes) occupied by the file.
    • May include file contents and metadata.

  5. Protection (Permissions)

    • Specifies who can read, write, or execute the file.
    • Commonly represented in Unix/Linux as: 
      rwx rwx rwx
      • Owner permissions (first set of rwx)
      • Group permissions (second set)
      • Others' permissions (third set)

  6. Ownership: Indicates the user (owner) and group associated with the file.

  7. Timestamps:

    • Provide information about key events related to the file:
      • Creation Time: When the file was created.
      • Modification Time: Last time the file's content was changed.
      • Access Time: Last time the file was accessed (read or written).

  8. File Status (Flags): Indicates special statuses such as: Hidden, Read-only, Archived, System (in Windows)

  9. Links:

    • Number of references (hard links) pointing to the file.
    • Used to determine whether the file is still accessible after deletion.

  10. File Identifier (Inode Number): A unique identifier for the file within the file system (used in Unix/Linux).

  11. File Content Attributes: Compression status, Encryption status

  12. System Attributes (OS-Specific):

    • Immutable flag (Linux): File cannot be modified.
    • No backup flag (MacOS): Excludes the file from system backups.

Some Other Attributes May Include:

Attributes related to flags. These Flags control or enable some specific property:

  • Read-only flag: 0 for read/write; 1 for read-only.
  • Hidden flag: 0 for normal; 1 for do not display in listings of all files.
  • System flag: 0 for normal files; 1 for system files.
  • Archive flag: 0 for has been backed up; 1 for needs to be backed up.
  • ASCII/binary flag: 0 for ASCII file; 1 for binary file.
  • Random access flag: 0 for sequential access only; 1 for random access.
  • Temporary flag: 0 for normal; 1 for deleted file on process exit.
  • Lock flags: 0 for unlocked; nonzero for locked.

Attribute related to keys. These are present in files which can be accessed using key:

  • Record length: Number of bytes in a record.
  • Key position: Offset of the key within each record.
  • Key length: Number of bytes in the key field.