freebsd下mount命令挂载与卸载光驱，挂载与卸载USB。
挂接光驱 mount -t cd9660 /dev/acd0 /cdrom 卸载光驱 umount -f /cdrom
挂接USB mount -t msdos /dev/da0s1 /mnt/usb 卸载USB umount /dev/da0s1
