Root user can't do everything? [closed]

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http://unix.stackexchange.com – Possible Duplicate: Redirecting stdout to a file you don’t have write permission on I'm quite new to Linux and I have a permissions questions. I'm using Linux Mint. If I go to /opt and do a $ echo hi > file it says permission denied. If I try with sudo, like this $ sudo echo > file it says permission denied. Isn't sudo to execute the command as superuser? How do I get permission denied as SU? If I do a $ sudo su and after that I do a $ echo > file it works. Is sudo su not the same as sudo? (HowTos)