[kubuntu] no longer able to use "sudo" command

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http://ubuntuforums.org – Whilst attempting to install some tricky software (for astronomical data reduction) I hit software installation problems running as sudo. I therefore tried the same thing running as my normal user, after modifying the permissions of /usr: chmod -R 777 /usr This was intended to be a temporary mod and seems to have been a bad idea. I now cannot log in or run commands as superuser: >> sudo su or >> sudo chmod -R 755 /usr gives the error message "sudo: must be setuid root" Various other things are wrong (e.g. my battery and networking is no longer det (Hardware)