KVM Alternatives for Linux

If you have multiple computers on your desktop there are a number of scenarios for using them:

• Many keyboards and mice all around your work space, a pair for each system.
• Remote desktop for VNC where you lose all the screen real estate on your secondary computers and end up with their desktops showing in a window on your primary computer.
• Physical KVM switch with all of the cords running in and out of that to the computers
• x2x software utility

x2x aka X Windows to X Windows Connection Utility

• works between 2 computers
• free and open source

x2x allows the keyboard and mouse on one ("from") X display to be used to control another ("to") X display. Since x2x uses the XTEST extension, the "to" X display must support XTEST.

If x2x is built under Cygwin (on Windows XP or Windows 2000) then the -fromwin option may be specified to allow the "from" display to be the Windows desktop. (The Cygwin build also supports use of an X display for the "from" screen). Use of -fromwin sets the default behaviour as if the -big -west -capslockhack options had also been given.

In the default interface, x2x puts a window on the "from" display. This window is labeled with the name of the "to" display. Keystrokes typed into this window go to the window on the "to" display that has the input focus. Clicking on the x2x window causes the mouse on the "from" display to control the cursor on the "to" display. Performing a subsequent multiple button click on the "to" display returns control to the "from" display.

If the -fromwin, -north, -south, -east or -west options are specified on the command line, x2x starts up with a different interface. When the mouse moves to the top, bottom, east side or west side of the default screen on the "from" display, the cursor slides over to the "to" display. When the mouse returns to to side of the "to" display that it entered, it slides back onto the "from" display.

Unless the -nosel option is specified, x2x relays X selections from one display to the other. (If -fromwin is specified then the X selection is relayed to and from the Windows clipboard as text strings).

Here are a few hints for eXcursion users (based on Intel version 2.1.309). First, use the -big option. Second, in the control panel, under mouse, check the box that enables "Automatically Capture Text on Button Up." X selections will then automatically move into the Windows clipboard. As is the case with all X applications running on 2.1.309 (including x2x), you will need to do an extra mouse click after performing the X selection for this operation to work. x2x is known to work poorly with eXcursion running on Windows 95, probably due to the Windows 95 task scheduler. x2x does work well with eXcursion running on Windows NT.

The hints for eXcursion are also valid for Exceed, with the exception that X selections work better, as long as you are using x2x version 1.25 or later.

Command 'x2x' can be installed with:

sudo apt install x2x

You only need to install x2x on the slave machine, the one whose keyboard and mouse you are NOT using.

On the SLAVE computer you will want to enable X11Forwarding

sudo vi /etc/ssh/sshd_config

#   ForwardX11 no

This is remarked out so X11 forwarding is already enabled

X11Forwarding yes

SSH to the SLAVE computer from your MASTER computer and run x2x:

ssh -X 192.168.x.x 'x2x -east -to :0'

Where -X option tells ssh to enable X forwarding. The EAST indicates which side of your screen will pass the mouse to the second display. Now you should be able to move your mouse between the two X sessions by moving your mouse off the screen to the right (east).

Instead of using -east or any screen pass parameter you can use the box window method. The -geometry argument is only to be used if you don't use north, south, east or west. It pops up a X window which, when you click in it, will activate the mouse and keyboard on the "to" desktop. To leave that desktop, you have to press two mouse buttons whilst over the x2x X window on the "from" desktop. (The mouse still moves over your home "from" desktop whilst in the remote "to" desktop.)

In this example we still use a separate mouse on the slave computer and we share a keyboard. A window appears we can click to control the slave computer.

ssh -X 192.168.x.x 'x2x -geometry 320x200 -nomouse -to :0'

Disable annoying "The authenticity of host can't be established" error messages: In this example we can move the mouse off the screen to the right onto the next computer, and when we launch this we are not hassled about adding an ECDSA key for the host. If it is your private LAN and your two hosts, the extra security is likely not necessary.

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -X 192.168.x.x 'x2x -east -to :0'

As you already know, your ssh hosts file is typically at /home/username/.ssh/known_hosts and thus we can choose a null file to avoid "REMOTE HOST IDENTIFICATION HAS CHANGED" messages.

Synergy, a software KVM solution that supports more than 2 computers

• works between 2 or more computers
• commercial license with future free availability questionable (they may move it to subscriptionware)

Synergy lets you share a single mouse and keyboard between multiple computers (even with different operating systems) without the need for special hardware. It is intended for users with multiple computers on their desk since each system uses its own monitor.

Redirecting the mouse and keyboard is done by moving the mouse off the edge of your screen. Synergy also merges the clipboards of all the systems into one, allowing cut-and-paste between systems. Furthermore, it synchronizes screen savers so they all start and stop together and, if screen locking is enabled, only one screen requires a password to unlock them all.

After installation you will note it is available two ways, Synergy Premium is the non-free version.

sudo apt-get install synergy

or for the debian package way

sudo dpkg -i synergy-1.5.0-r2278-Linux-x86_64.deb

Synergy uses a GUI configuration applet that you can find under the menu, maybe under the Accessories menu depending on your desktop manager.

You have to do some configuration before you get it up and running. There are lots of configuration pages.

You can use the command line to run Synergy too.

note: Work on Synergy has stalled due to Symless (the company behind Synergy) halting further development of the the 1.x branch and concentrating on 2.x branch, which is primarily closed-source, configured through a hosted web interface and requires a paid subscription. A fork called Barrier was created to continue development of the 1.x branch, containing many bug fixes and new features.

Dear Nick Bolton - stop screwing over the Open Source community that got you were you are with this software. No matter how you paint a turd, it's still a turd, and so are you.

barrier-kvm - Because Symless is a bastard company and Nick Bolton is slime

• works between 2 or more computers
• free (what license?)

Barrier is KVM software forked from Symless's synergy 1.9 codebase. Synergy was a commercialized reimplementation of the original CosmoSynergy written by Chris Schoeneman.

Not available via apt. Use snap (i guess). not much info here!