I found this native emulator for GNU / Linux called lxdream. lxdream is a new Sega Dreamcast emulator for Linux.
To install simply download the file you need for your distro from this link
You can also download through the official repositories.
For Ubuntu
First edit the list by entering the terminal and typing:
$ sudo gedit /etc/apt/sources.list
Enter the following lines.
deb http://www.lxdream.org/debian unstable main
deb-src http://www.lxdream.org/debian unstable main
Save and type
$ sudo apt-get update
$ sudo apt-get install lxdream
You must download and flash the bios rom Dreamcast
Find the program in Menu> Applications> Games> lxdream, select and open the program, the first thing you should do is go into Settings> Routes and tell the program where files are located and bios flash rom you downloaded.