[ubuntu] group permissions

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http://ubuntuforums.org – When i plug a usb disk into my ubuntu 12.04 machine. It is mounted with the owner root and the group disk. On this system i also have a normal user called nice. But nice cannot be allowed to write to the usb disk (copying over folders). Because the user does not have permissions to the usb disk. So since the usb disk is owned by root and in the group disk (where disk have rw- permissions), i added my nice user to the disk group. But still i cannot get the group permissions to write to the disk. Anyone who can give their 5 cents so i can copy over folders with my normal nice user? T (Hardware)