An inode stores basic information about a regular file, directory, or other file system object. It contains a list of direct, indirect, and doubly and triply indirect pointers. On some FileSystems, very small files can be stored directly in the Inode itself.

The inode number is a unique integer assigned to the device upon which it is stored. All files are hard links to inodes. Whenever a program refers to a file by name, the system conceptually uses the filename to search for the corresponding inode.

Sophisticated FileSystems create Inodes on demand, but with most, the number of Inodes on a Partition has to be decided on during FileSystem creation. It is rare to run out of Inodes unless you have an unusual usage profile such as storing a news spool or Squid cache. Exhaustion of the inodes will prohibit the creation of additional files even if sufficient HDD space exists.

How many Inodes do I have free?

• df - i

What information does an Inode store?

Note : Inodes do NOT contain filenames.

• The size of the file in bytes.
• The file's physical location (the addresses of the blocks of storage containing the file's data on a HDD)
• The file's permissions.
• The Device ID
• The User ID of the file's owner.
• The Group ID of the file.
• Timestamps (ctime,mtime and atime). See FileTimes?
• A reference count telling how many hard links point to the Inode.

View Inode Information for a particular file.

For example PhilMurray's famous macaroni and cheese recipe:

$stat macaroni_and_cheese

  File: `macaroni_and_cheese'
  Size: 1965            Blocks: 8          IO Block: 4096   regular file
Device: 305h/773d       Inode: 2775423     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/    staz)   Gid: ( 1000/    staz)
Access: 2007-05-16 00:21:17.000000000 +1200
Modify: 2007-05-16 00:21:16.000000000 +1200
Change: 2007-05-16 00:21:16.000000000 +1200

How to obtain a file's Inode number

• ls -i <file>