Dev mode is not the same as being rooted. Even is you do download Ubuntu there are extra steps you would need to be taking in order to get it to install. Once installed it's probable that you would only be able to access your phone by SSHing into to, and it wouldn't actually be a working phone anymore!
*I'm not saying this is not possible - it is, but I'm not sure you realize what you are getting into!
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Dev mode is not the same as being rooted. Even is you do download Ubuntu there are extra steps you would need to be taking in order to get it to install. Once installed it's probable that you would only be able to access your phone by SSHing into to, and it wouldn't actually be a working phone anymore!
*I'm not saying this is not possible - it is, but I'm not sure you realize what you are getting into!