What is inode number in Linux ?

An inode is an entry in inode table, containing information ( the metadata ) about a regular file and directory. An inode is a data structure on a traditional Unix-style file system such as ext3 or ext4.

What is inode number in Linux

Inode number also called index number, it consists following attributes.

• File types ( executable, block special etc )
• Permissions ( read, write etc )
• UID ( Owner )
• GID ( Group )
• FileSize
• Time stamps including last access, last modification and last inode number change.
• File deletion time
• Number of links ( soft/hard )
• Location of ile on harddisk.
• Some other metadata about file.

To check inode number of file use following command. The first field in output is an inode number of the file.

ls -il  myfile.txt

1150561 -rw-r--r-- 1 root root 0 Mar 10 01:06 myfile.txt

You can also search file with an inode number using find command. For example:

find /home/rahul -inum 1150561

/home/rahul/myfile.txt

Inode Changes with Copy, Move and Delete

What happens with inode number when copy, move or delete a file on file system.

Copy file: cp allocates a free inode number and placing a new entry in inode table.

### Check inode of existing file 
ls -il  myfile.txt
1150561 -rw-r--r-- 1 root root 0 Mar 10 01:06 myfile.txt

### Copy file with new name 
cp myfile.txt myfile_new.txt

### Check inode number of new file. Its changed 
ls -il myfile_new.txt
1150562 -rw-r--r-- 1 root root 0 Mar 10 01:09 myfile_new.txt

Move or Rename a file: if destination is same filesystem as the source, Has no impact on inode number, it only changes the time stamps in inode table.

### Check inode of existing file 
ls -il  myfile.txt
1150561 -rw-r--r-- 1 root root 0 Mar 10 01:06 myfile.txt

### Moved file to another directory 
mv myfile.txt /opt/

### Check inode number of moved file. No change in inode 
ls -il /opt/myfile.txt
1150561 -rw-r--r-- 1 root root 0 Mar 10 01:06 /opt/myfile.txt

Delete a file: Deleting a file in Linux decrements the link count and freeing the inode number to be reused.