Chrome OS = 'Normal' Linux?

I recently changed my Chromebook to dev mode and now using Chrome OS, which supposedly is the same thing as 'normal' Linux. Is this true or must I use a more 'normal' kind of Linux, like Ubuntu or Debian? So far, everything seems to work fine on Chrome OS, except for the head command which does not show me the first 10 lines of a text file, even though it is supposed to. Then again, I just started using Linux so I don't know. Thanks!