I have an ext4 partition with 120 MB total space. Command df shows that the partition is %91 utilized. I am only able to see about 19 MB of files on the partition using ls -a. Any ideas on where the space is used?

Have you looked at fdisk -l /dev/sda? (If the partition is on your first hard drive, sdb for second, etc.)

When you state that you "only see" ~19Mb of files, how were you "looking?" If, for example, the ext4 fs is your root file system, it would contain a lot of file owned by "root" to which you would not, normally, have access. Thus they would not be displayed in, for example, a ls of your home directory.

You could, perhaps, do a sudo find / -size 2G to list all files of size 2Gb or more (or 2M for 2 Mb or more, etc.) to see if you have some exceptionally large files on your drive.

You might want to look at the output of mount. Perhaps you've linked space on that partition to some other location so it doesn't show up when you look.

Try using the du command. For example, to see the amount of space occupied by each subdirectory one level below the directory that the partition is mounted on, you could do:

If it's not clear what that means let us know. It might be better to be root if you don't otherwise have permission to see all of the files on the partition.