[ubuntu] cant login as super user Authentication failure,for a previously accessed password

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http://ubuntuforums.org – i cant login as super user using su command ,previously it was successful and i am sure that password is correct,previosly there was an issue by changing file permission of www folder and i follow this link to correct ithttp://sysadminnotebook.blogspot.in/...ssions-to.html after that i cant login as su (Hardware)