So yesterday I failed to have my arduino duemilenove connect to linino. I spend all day trying to find out what was wrong.
I’m not going to bother you with how hard it was for me to solve this and simply tell you what you need to do.
Basically the problem was that linino does not come with the usb acm driver. You can install it via the web or via the command line.

opkg install kmod-usb-acm

This works with UNO, mega, mega adk, due
But it does not work with duemilenove and I could not test the leonardo (I guess due to the dual com port issue)
While you are at it also install minicom. This is a serial monitor that allows you to connect to your arduino.

opkg install minicom

reconnect your arduino to the com port and run

ls /dev/ttyA*

you should see ttyACM0

If you see it run
minicom ttyACM0
This command will not connect you to ttyACM0 but it will use the configuration file ttyACM0. So if we configure minicom correctly the next time we run “minicom ttyACM0” it will connect to ttyACM0.
The configuration is as follows
press ctrl+A->O select port settings and then set the baut rate to the rate you usually use and the port to /dev/ttyACM0
Save the settings in the config file.
exit minicom
ctrl+A -> x -> yes
restart minicom
minicom ttyACM0
and now you have a serial connection to the arduino connected to the usb port of your yun.
If you have ssr_demo_part_2 running from one of my previous parts you see the logging flow. you can use SET to see the values you can set and everything else I explained.

But lets take it a bit further. After all you need to start putty, start minicom in putty. Why not simply working locally.
To do so load the package ser2net
modify /etc/ser2net.conf
remove all the default configurations and add
Note that the last part is the baut rate of the serial monitor so I should match the number in Serial.begin(115200) of the running sketch.
run ser2net (not sure this is needed but I did 😉 )

Now start your standard telnet program on your local machine. (I use putty)
connect to your yun on port 2001 with the telnet protocol.
And you have your serial monitor 🙂