The inode is a unique identifier in Linux/UNIX filesystems, it’s also known as the index number.

Definition on nixCraft: An inode is a data structure on a traditional Unix-style file system such as UFS or ext3. An inode stores basic information about a regular file, directory, or other file system object.

We can display the inode of a specific file name or a list of files in a directory by using the ls command.

Here is a typical output of files inode inside a directory,

1
2
3
4
5

$ ls -li
total 13
10376896 -rw-r--r--  1 draco  draco   200 Feb 11 19:01 test.c
10376892 -rw-r--r--  1 draco  draco   480 Feb 11 19:11 test.hex
10376897 -rw-r--r--  1 draco  draco   181 Feb 11 19:10 test

The numbers are the inodes of the respictive files.

One of the most common use of inodes is handling filenames with special characters or unicode like UTF-8, you cannot handle such filenames directly from the terminal, so you need to access it using its inode number.

My answer on StackOverflow to a related problem: http://stackoverflow.com/a/16216044/1708778

— Further reading: Understanding Filesystem Inodes (BSD DEVCENTER ONLamp.com)