authentication failure when setup new password

Hello friend , 
        you are prompted to this shap while opening your F5 Big-IP appliance first time. 
you need to use the default credentials first as below : 
> localhost login : root 
> Password : default

>(current) UNIX password: default 
" enter the default Password again for UNIX " 

After That you are prompted to set the new root Password and Confirmation as well. 

Then , F5 Command line Bash prompt will appear for you.

I hope my reply meets your needs. 🙂