Nov 29, 2013

Synergy, Security, and Tips

This article introduces how to set up synergy, a tool which lets you easily share your mouse and keyboard for multiple computers.

Introduction

The Forge

More displays mean better productivity to me. Currently, I’m using five — two for emacs, one for terminal, one for email, one for web search — and I find them very useful.

Ideally, you may have a computer and a special hardware such as KVM switches or Matrox TripleHead2Go which connects multiple monitors to a single machine. However, they are pretty expensive and not an option for a poor graduate student like me.

The alternative is to have multiple machines, each connected to one or two displays. Then, you can use synergy to control them with a single mouse/keyboard. In my case, I have two desktops and one laptop. With shared clipboard feature, you have an illusion of having a single machine with multiple displays.

Basic Setup

In this article, I explain the set up based on my configuration. I have Macbook Air, iMac, and a Linux machine. We will install synergy server on the Linux machine and two clients on Macbook Air and iMac.

Linux (server)

Download and install synergy from the webpage.
I’m using version 1.4.12, protocol version 1.4
Save the following file as ~/.synergy.conf. You may need to edit screens and links section. You also need to provide an IP address of each machine in aliases section.

# +--------+ +--------+ +-------+
# | Mac Air| | Linux  | | iMac  |
# +--------+ +--------+ +-------+

section: screens
Linux:
halfDuplexCapsLock = false
halfDuplexNumLock = false
halfDuplexScrollLock = false
xtestIsXineramaUnaware = false
switchCorners = none
switchCornerSize = 0

iMac:
halfDuplexCapsLock = false
halfDuplexNumLock = false
halfDuplexScrollLock = false
xtestIsXineramaUnaware = false
switchCorners = none
switchCornerSize = 0

MacAir:
halfDuplexCapsLock = false
halfDuplexNumLock = false
halfDuplexScrollLock = false
xtestIsXineramaUnaware = false
switchCorners = none
switchCornerSize = 0
end

section: links
Linux:
right = iMac
left = MacAir
iMac:
left = Linux
MacAir:
right = Linux
end

section: options
relativeMouseMoves = false
screenSaverSync = true
win32KeepForeground = false
switchCorners = none
switchCornerSize = 0
end

section: aliases
Linux:
<IP of Linux>
iMac:
<IP of iMac>
MacAir:
<IP of MacAir>
end

You can start synergy daemon by typing

synergys --daemon --name Linux -c ~/.synergy.conf

Mac (client)

I found problems using the client that I get from http://synergy-foss.org. It seems Quicksynergy works on my Mac machines. You can start the client by typing

/Applications/QuickSynergy.app/Contents/Resources/synergyc \
                            --name <CLIENT_NAME> localhost

In my configuration, <CLIENT_NAME> is either iMac or MacAir.

Security Issue

The above setup has a security issue. Whatever you type will be sent from the server (Linux) to the other machines (iMac/MacAir) as a plain text. It means that any computer in the same network can see what you type including passwords. This could be problem if you are on a school/company network.

Synergy recently started to provide encryption methods. However, there is a recent article discussing the problem of the current encryption methods and possible attacks on them.

However, we can still rely on SSH tunneling. Simply put, we create a secure channel of communication between a server and clients. Then, let synergy use the channel to exchange information.

In server (linux), we start synergy daemon with --address :24800 option to specify the port number which we use as a tunnel.

/usr/bin/synergys --daemon --name Linux -c ~/.synergy.conf --address :24800

In client, we first establish the SSH tunnel and run synergy client:

ssh -f -N -L localhost:24800:<SERVER-HOSTNAME>:24800 <SERVER-HOSTNAME>
/Applications/QuickSynergy.app/Contents/Resources/synergyc \
                                        --name <CLIENT_NAME> localhost

Here <SERVER-HOSTNAME> is either IP address or domain name of the server.

Tip: Keyboard Shortcut to Navigate Screens

Having multiple monitors create a new problem. It takes some time to move the mouse pointer from one side to the other side (in my case, it’s about 5400px to cross). Fortunately, synergy provides a solution for this problem. You can add the following to the ~/.synergy.conf file on the server.

section: options
keystroke(shift+alt+left) = switchInDirection(left)
keystroke(shift+alt+right) = switchInDirection(right)
end

Now you can press shift+alt+left/right to move the focus to the left and right.

Tip: Wakeup Script

There is a possible problem when the computers go to the sleep mode. You can wake up the computer which has a mouse and keyboard connected. However, there are no ways to wake up the other machines. In my case, they are Mac machines and I found the following “wakeup” script from the web.

#include <CoreFoundation/CoreFoundation.h>
#include <IOKit/IOKitLib.h>

#include <iostream>

void set_request_idle(bool request)
{
    io_registry_entry_t entry = IORegistryEntryFromPath(kIOMasterPortDefault,
            "IOService:/IOResources/IODisplayWrangler");
    if (entry == MACH_PORT_NULL) {
        return;
    }

    IORegistryEntrySetCFProperty(entry, CFSTR("IORequestIdle"),
            request ? kCFBooleanTrue : kCFBooleanFalse);

    IOObjectRelease(entry);
}

int main(int argc, const char **argv)
{
    const std::string &command = (argc > 1) ? argv[1] : "";

    if (command == "idle") {
        set_request_idle(true);
    } else if (command == "wake") {
        set_request_idle(false);
    } else {
        std::cerr << "usage: " << argv[0] << " (idle|wake)\n";
        return 1;
    }

    return 0;
}

You can save the file as wakeup.cc and compile it on Mac as follows.

clang++ -Wall -O3 -framework Foundation -framework IOKit wakeup.cc \
        -o ~/bin/wakeup

Then you can ssh from the server to a client and remotely execute the wakeup script as follows:

(SERVER) $ ssh <CLIENT_IP> "~/bin/wakeup wake"

posted at 3:30 pm · blog

Soonho Kong