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What is an Inode Number in Linux?

What is an Inode Number in Linux? 

Linux considers all hardware devices, printers, directories, and processes to be files. A regular file may be any text, audio, video, photograph, or multimedia file. All standard files have metadata that describes everything about the file, such as sort, Inode, and so on.

An inode number in Linux is a row in the Inode table that contains data (metadata) about a regular file or directory. In a traditional Unix-style file system like Ext3 or Ext4, an inode is a data structure.

What is an Inode Number in Linux?

In Linux and other Unix-like environments, an inode number is a unique identifier for all files. When a file is created on a system, it is given a file name and an Inode number.

The inode number, also known as the index number, is made up of the following file attributes:

  • Types of files ( executable, block special, etc )
  • Permissions ( read, write, etc )
  • UID (Unique Identification Number) ( Owner )
  • GID ( Group )
  • Size of the file
  • Last access, last modification, and last inode number change are all included in the timestamps.
  • Deletion time
  • Number of soft/hard links
  • The location of the file on the hard disk.
  • Some metadata about the file.

Find the Inodes on the Filesystem

Using the ‘-i‘ option with the df command, you can find the total number of inodes on the disk.

df -i /dev/sda1

Filesystem      Inodes   IUsed   IFree     IUse% Mounted on
/dev/vda1       1536000  138846  1397154   10%   /

The command below displays the total number of inodes on the file system, as well as the number of used and free inodes. You can not generate a new file on disk if inodes are full on any filesystem, even if there is enough free space. To create files, each file system needs free disk space and inodes.

Find a file’s inode number

Use the following command to find the file’s inode number. The first field in the output is the file’s inode number.

ls -il  myfile.txt

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

You can also use the find command to look for a file by inode number. As an example:

find /home/rahul -inum 1150561


Copy, Move and Delete Inodes

When you copy, move, or delete a file on the filesystem, what happens to the inode number?

Copy file: cp creates a new entry in the inode table by allocating a free inode number.

### 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 the destination filesystem is the same as the source, moving or renaming a file has little effect on the inode number; it just affects the timestamps in the 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: In Linux, deleting a file decreases the link count and frees the inode number for future use.

Remove unused files to free inodes

In case if inodes are full. You will have to remove unused files to make inodes free on the filesystem. On disk, there is no way to increase or decrease inodes. It is only created when a filesystem is created on a disk.

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