Tente usar o seguinte comando:
ls -alhrt /dev/* | tail -n 30
procurando datas, você pode obter o resultado do nome dos dispositivos usb. Para mim, a seguinte saída foi produzida:
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:2 -> ../ram2
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:14 -> ../ram14
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:0 -> ../loop0
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:3 -> ../ram3
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:15 -> ../ram15
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:2 -> ../loop2
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:11 -> ../ram11
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:10 -> ../ram10
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:5 -> ../loop5
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:8 -> ../ram8
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:9 -> ../ram9
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:7 -> ../ram7
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:5 -> ../ram5
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:4 -> ../loop4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:4 -> ../ram4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:6 -> ../ram6
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:7 -> ../loop7
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:6 -> ../loop6
lrwxrwxrwx 1 root root 6 Apr 29 03:26 8:0 -> ../sda
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:9 -> ../sda9
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:2 -> ../sda2
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:4 -> ../sda4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:6 -> ../sda6
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:3 -> ../sda3
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:7 -> ../sda7
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:8 -> ../sda8
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:5 -> ../sda5
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:1 -> ../sda1
drwxr-xr-x 16 root root 4.2K Apr 29 03:26 ..
drwxr-xr-x 2 root root 720 Apr 29 2012 .
de lá, pegue o nome do dispositivo usb, vamos chamar o tempo de "usbdev".
Em seguida, digite o seguinte comando para montá-lo.
mount -t ext3 /dev/usbdev /media/USB_Bkup