How to overclock bfgminer on raspberry pi?

[wolfEXE57]

so im mining bitcoin through my raspberry pi and i cant figure out how to over clock it
i have 4 antminer U2's that idle around 2 Gh/s
i would like them to get up as i have overclocked them through my computer on cgminer
but the raspberry pi is different then just using a normal windows terminal
 i tried adding the "--set-device antminer:clock=0B81" to the end of my launch command but it dosent overclock
any help? im verry new to this >_>

heres the code im using
screen -S Mining ./bfgminer -o stratum.bitcoin.cz:3333 -u USERNAME -p PASSWORD  --set-device antminer:clock=0B81
(obvously im withelding my mining info from the launch code)

[chrisvl]

Hash Rate Clock setting

1.6ghs x0781

1.8ghs x0881

2.0ghs x0981

2.2ghs x0A81

[chrisvl]

Try this bfgminer -S all -o <pool-server> -u <pool-user> -p <pool-pass> --set-device antminer:clock=0B81

[chrisvl]

Try this bfgminer -S all -o <pool-server> -u <pool-user> -p <pool-pass> --set-device antminer:clock=0B81

on clock you can set the hashrate
Hash Rate Clock setting

1.6ghs x0781

1.8ghs x0881

2.0ghs x0981

2.2ghs x0A81