but Ubuntu was the first popular Linux distribution to go sudo-only by default. When you install Ubuntu, the standard root account is created, but no password is assigned to it. You can't log in as root until you assign a password to the root account...
External SD cards are usually formatted in FAT32 or exFAT file systems which don't have support for unix permissions (chmod/chown) and special files such as sockets or symlinks. Also, Android enforces ''noexec'' mount option for user's storage, so you won't be able to execute binaries...