Every partition in GNU/Linux has its own file system.
In a file system, a file is represented by an inode. Inodes are data structures that contain information about files that are created when a file system is created. Each file has an inode and is identified by an inode number in the file system where it resides. Every partition has its own set of inodes.
Each inode describes a data structure on the hard disk, storing the properties of a file, including the physical location of the file data. When a hard disk is initialized, a fixed number of inodes per partition is created. This number will be the maximum amount of files, of all types (including directories, special files, links etc.) that can exist at the same time on the partition. Usually 1 inode per 2 to 8 kilobytes of storage.
When a new file is created, it gets a free inode. The following information are stored in inode.
• Owner and group owner of the file.
• File type
• Permissions on the file.
• Date and time of creation, last read and change.
• Date and time this information has been changed in the inode.
• Number of links to this file
• File size
• An address defining the actual location of the file data.
The only information not included in an inode, is the file name and directory. These are stored in the special directory files. By comparing file names and inode numbers, the system can make up a tree-structure that the user understands.
If you want to the inode number associated with a file, use "ls" command use "-i" option.