Unable to create folder/file on root in spite of free space
Solution 1:
This is your problem:
/dev/sda1 2681728 2681728 0 100% /
You have no inodes free. You will need to delete files to free up inodes if you would like to write anything more on that file system. There is no way to increase the number of inodes once the file system has been created.
You should still be able to write to /home and /usr though.