После вставки флешки нужно понять, как она определилась. Можно использовать один из вариантов
# rmformat
Looking for devices...
1. Logical Node: /dev/rdsk/c3t1d0p0
Physical Node: /pci@0,0/pci8086,2829@d/cdrom@1,0
Connected Device: VBOX CD-ROM 1.0
Device Type: DVD Reader
Bus: <Unknown>
Size: <Unknown>
Label: <Unknown>
Access permissions: <Unknown>
2. Logical Node: /dev/rdsk/c4t0d0p0
Physical Node: /pci@0,0/pci106b,3f@6/storage@2/disk@0,0
Connected Device: USB FLASH DRIVE PMAP
Device Type: Removable
Bus: USB
Size: 3.9 GB
Label: <Unknown>
Access permissions: Medium is not write protected.