[ubuntu] how to manage premission for user group for internal harddisk partitions

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http://ubuntuforums.org – someone suggest me that for managing permission for accessing the partitions of hard disk you should add users to group and now i have found from askubuntu.com that how to add user to groups. But i not get the way how to add permissions for users in such a way that they not have access to specific hard disk partition but they have access to other partition without use of admin password? after mounting partition in admin user when i go to properties and then to permission and their try to change the premissions something like access to files/folder and groups then when i change the gro (Hardware)