What is the Scoreboard
The ScoreboardFile is used by proftpd for tracking information for each current FTP session. It is necessary for things like MaxClients, MaxClientsPerUser, etc. The utility programs (ftpwho, ftpcount, ftptop) read the scoreboard and display its information.

Here's how proftpd handles its scoreboard: There is a default path that proftpd will use for writing its scoreboard (var/proftpd/proftpd.scoreboard). This default path depends on how you install proftpd (i.e. if you install from source and use the --prefix configure option, the default path will be adjusted to honor your --prefix). However, you can also explicitly tell the daemon what location to use for its scoreboard using the ScoreboardFile configuration directive in your proftpd.conf. When the daemon starts up, it looks to see if there is a scoreboard already there; if there isn't, it makes a new one.

The most common error encountered when opening the scoreboard is:

  unable to open scoreboard: No such file or directory

Frequently Asked Questions
Question: Why doesn't proftpd create the needed directories, if they're not there, when opening the scoreboard?
Answer: The short answer is because that is the job of the system administrator, not the application. The long reason is that proftpd does not know the filesystem layout being used, and does not know what sort of permissions should be given to any directories it might need to create for its scoreboard.

Question: Can I copy my scoreboard from one server to another?
Answer: No. ScoreboardFiles cannot be copied from server to server; they are specific to that particular installation.

In the same fashion, you should not try to place the scoreboard on an NFS filesystem. First, attempting to share the scoreboard is not supported, and will only lead to trouble. Second, NFS does not support file locking, which proftpd requires for handling the scoreboard.

Question: Why do I see "scrubbing scoreboard" in my debugging output?
Answer: There is a bad habit among system administrators of using `kill -9' to kill a misbehaving process. Any process that is terminated this way, though, does not have a chance of properly shutting down. Administrators would use `kill -9' on some of proftpd's session processes, which means that they would not be able to remove themselves from the scoreboard. ftpwho and ftptop would show sessions that no longer existed.

The chance of changing this bad habit in system administrators is slim, so proftpd was changed to check the scoreboard periodically. It will scan the entire scoreboard file, and for each scoreboard session listed, it asks the operating system if that session process is still alive. If the answer is no, the entry is removed from the scoreboard. This process is known as "scrubbing".