Mtx(1) is a set of low level driver programs to control features of SCSI
backup related devices such as autoloaders, tape changers, mediajukeboxes,
and tape drives. It can also report much data, including serial numbers,
maximum block sizes, and TapeAlert(tm) messages that most modern tape
drives implement, as well as do raw SCSI READ and WRITE commands to
tape drives.

It works like chio(1) but supports more features and drives and runs in
users land. There are some amanda (misc/amanda24-server) scripts, which
depend on mtx.