cmShelfCommand is a read-write enumeration that lets an administrator restart just one shelf by setting it to restart(2), instead of using cmSysCommand to reboot the entire multi-shelf system. This is useful when only one expansion shelf is misbehaving and the operator wants to avoid disrupting subscribers on other shelves. For example, if shelf 3 stops responding to management queries while shelves 1 and 2 remain healthy, the operator would SET cmShelfCommand to restart(2) against shelf 3's table entry rather than restarting the whole chassis.