[linux-audio-user] Unencrypted remote X11 app, Was: headless audio apps

[Benno Senoner]

It's probably because you use X11 over ssh.

If you ssh from machine A into machine B , normally ssh forwards the X11 
protocol
too
, just look at $DISPLAY
if it's something like localhost:10.1
then you are using ssh.
While the nice advantage of ssh is that you don't have to fiddle with 
xhost to authorize
the remote host to display on your local machine and at the same time 
all X11 traffic is encrypted
(so even a potential sniffer on the LAN would not be able to figure out 
what you type on the keyboard etc)
the big drawback is that encryption is relatively CPU heavy.
And since audio apps have all those nice peak meters, scroll waves in 
real time on the screen etc,
you can imagine that this causes lots of requests to the X server which 
translates into lots of X traffic
which in turn needs to be encrypted if it runs over ssh.

If you want to run remote X11 apps over an unencrypted connection do the 
following:

you can still ssh from machine A to machine B.
then do:
on machine A: (where you want to display the output of the app)

xhost +IP_OF_MACHINE_B
eg
xhost +192.168.0.2

(this tells the X server running on machine A that machine B is allowed 
to display on
machine's A screen)

on machine B do:

export DISPLAY=IP_OF_MACHINE_A:0.0

eg

export DISPLAY=192.168.0.1:0.0

(the export DISPLAY=.... command tells to X apps running on machine B
that they should send the X11 output to the IP of machine A)

Keep in mind that X11 normally runs over TCP port 6000 thus make sure that
this port is open on machine A or at least place an iptables rule
to open TCP port 6000 so that machine B can connect to.
(check your firewall settings)

Now when you run an application on machine B
the X11 traffic is forwarded at full wire speed of your connection 
without causing too much
additional load.

cheers,
Benno
http://www.linuxsampler.org


robin fell wrote:

>Hello
>
>[apologies for remotely on-topic post - i'm  an X noob]
>
>Has anyone on the list any useful anecdotes about running X apps
>remotely (through ssh in my case) and having strange problems?
>
>Since I'm still in the process of setting up a terminal I haven't gotten
>a full list of the misbehaving apps - but I have seen ~30% load increase
>(as reported by an admittedly old qjackctl) upon starting meterbridge
>remotely (vs starting locally).  
>
>I'm wondering if this is something I have this set-up incorrectly....
>
>[I'd also be interested if anyone has any measurements for the
>performance benefits of remoting audio apps.]
>
>cheers
>Rob
>
>
>
>  
>