I won’t go into the details of what inodes are and why they are important, but when you run out of them, you can have all of the free disk space in the world and not be able to do a darn thing with it. An easy way to see how many inodes are being used on a linux system is with the df command
df -i
This will show you the number of inodes allocated to a file system and the number that are free. Likewise in solaris, the command is df but you use a different option to get the same information.
df -o i