Inodes
Inodes store metadata for files (permissions, UID/GID, timestamps, block pointers). Each filesystem has a fixed number of inodes created at format time.
Checking inode usage
Input:
df -i
Output:
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/sda1 3276800 85421 3191379 3% /
This shows inode availability per mounted filesystem.
References: