What is an iNode and how to check if they are exhausted?

iNode is a data structure in the file system of Unix-like operating systems that contains file metadata (size, permissions, modification time, pointers to data blocks, etc.), but does not contain the file name.

To check if iNodes are exhausted, you can use the command df -i, which shows the number of available and used iNodes on the file system. If the number of free iNodes is zero, new files cannot be created even if there is free space on the disk.

Example output:

df -i
Filesystem      Inodes  IUsed   IFree IUse% Mounted on
/dev/sda1      1000000 900000 100000   90% /

If IFree = 0, it means the iNodes are exhausted.