On occasion if you are trying to fdisk or mount a USB disk on Solaris 10 you may get an error that says "Cannot open device." For example:

# fdisk /dev/rdsk/c2t0d0s2
Cannot open device

Things to check:

• 1. Make sure you are root or have the correct user privilege
• 2. Try `devfsadm -Cv` to remove any stale disk entries
• 3. Stop volume management `svcadm disable volfs`