A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. A usage quota or block quota limits the amount of disk space that can be used. In addition, administrators usually define a warning level, or soft quota, at which users are informed they are nearing their limit, that is less than the effective limit, or hard quota. When a soft quota is violated, the system normally sends the user some sort of message. The user is then known to be "overquota". No further action can be taken because the system prevent disk write operations that would result in hard quota violations. No more files can be uploaded in the FTP repositories and no more e-mails can be received. E-mails are sent back to senders with the "overquota" indication. The solution is to delete some existing files to free some disk space or to set new quota limits.