[CentOS] Closing a multi-session disk

I have a disk which is not being recognised for reading, and I suspect that it may be a multi-session disk which has not been closed. K3b seems to agree with me, since it lists it as an appendable data cd. However, I can't find any way to close the session in k3b.

I thought I remembered that it was possible to do that in xcdroast - which is almost certainly the application that burned the disk in the first place. However, xcdroast tells me that no disk is loaded.

That brings me to ask those of you that use command-line burning if you know of any way I can close this disk. I suspect the files on it are ones that I don't have elsewhere.

Anne