If you have a Linux Synergy client connecting to a Synergy server on another machine, you’ll want the client to start up with GDM so that you can access the mouse and keyboard to log in. Here’s how to get it working Ubuntu, although it should work on other distributions too.
Edit the Default file
sudo gedit /etc/gdm/Init/Default
and add these lines to it
#Synergy - place this line somewhere before the "sysmodmap=/etc/X11/Xmodmap" line /usr/bin/synergyc serverComputerHostname
Where serverComputerHostname is the host name or IP of your Synergy server.
Also edit the PreSession/Default file:
sudo gedit /etc/gdm/PreSession/Default
And add these lines to it:
#Synergy - place this line somewhere before the "XSETROOT=`gdmwhich xsetroot`" line /usr/bin/synergyc serverComputerHostname
Logout and now you should be able to login to Ubuntu with your server’s keyboard and mouse.