Tim's Notes

Activity Log

Inode Table

2 min read

What is an Inode Table?

An inode (index node) table is a data structure in Unix-like file systems that stores key information about each file, except its name and data. Think of it as a database that the filesystem uses to keep track of file metadata and data block locations.

Structure of an Inode

Each inode contains:

  • File Metadata:
    • File type (regular file, directory, symbolic link, etc.)
    • File permissions (e.g., rwxr-xr--)
    • Owner and group IDs
    • File size
    • Number of links
  • Timestamps (access, modification, change)
  • Location of the file’s data blocks
  • Other Attributes

Key Concepts

  • Inode Number: A unique identifier for each file
  • Directory Entry: Maps filenames to inode numbers
  • Hard Links: Multiple directory entries pointing to same inode
  • Soft Links: Special files containing paths to other files
  • Block Pointers: Track file data locations on disk

Viewing Inode Information

You can easily check inode number using ls -i and view inode information with stat command:

# List inode number
devnyxie:~$ ls -i filename.txt
  9862203 filename.txt
# Display inode information
devnyxie:~$ stat filename.txt
  File: filename.txt
  Size: 0         	Blocks: 0          IO Block: 4096   regular empty file
  Device: 259,5	Inode: 9862203     Links: 1
  Access: (0664/-rw-rw-r--)  Uid: ( 1000/devnyxie)   Gid: ( 1000/devnyxie)
  Access: 2025-01-19 18:04:10.816862088 +0100
  Modify: 2025-01-19 18:04:10.816862088 +0100
  Change: 2025-01-19 18:04:42.024653510 +0100
  Birth: 2025-01-19 18:04:10.816862088 +0100

Inode in Action: How It Works

Interaction with Files

The role of inodes becomes clear when you interact with files by name. Here’s what happens when you run cat simple.txt:

  1. Directory Lookup:
    The system checks the current directory (or path) to find an entry for simple.txt. This entry maps the filename to its corresponding inode number (e.g., 9860740).

  2. Inode Retrieval:
    The system retrieves the inode structure from the inode table. This structure contains:

    • File type, permissions, owner/group, and timestamps.
    • Pointers to the data blocks where the file’s content is stored.

  3. Data Access:
    Using the inode’s block pointers, the system locates the file’s data blocks on the disk and outputs the content to your terminal.

Creating a file

When you create a file:

  1. The system allocates an inode
  2. Directory entry links filename to inode number
  3. File metadata gets stored in the inode
  4. Data block locations are recorded in the inode

Sources

Graph View

Backlinks

Tags