Eclipse UI tests fail with gtk_init_check() on a Redhat Jenkins server - eclipse

Question

When running Tycho UI tests for Eclipse on a Redhat server (6.7) via Jenkins, the Exception below occurs. I know that a graphical subsystem must be installed and running, but there seems to be something amiss with my setup. I already installed GTK via "yum groupinstall Desktop".
org.eclipse.swt.SWTError: No more handles [gtk_init_check() failed]
at org.eclipse.swt.SWT.error(SWT.java:4517)
at org.eclipse.swt.widgets.Display.createDisplay(Display.java:908)
at org.eclipse.swt.widgets.Display.create(Display.java:892)
at org.eclipse.swt.graphics.Device.<init>(Device.java:156)
at org.eclipse.swt.widgets.Display.<init>(Display.java:512)
at org.eclipse.swt.widgets.Display.<init>(Display.java:503)
at org.eclipse.ui.internal.Workbench.createDisplay(Workbench.java:790)
at org.eclipse.ui.PlatformUI.createDisplay(PlatformUI.java:162)
at org.eclipse.ui.internal.ide.application.IDEApplication.createDisplay(IDEApplication.java:169)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:111)
at org.eclipse.tycho.surefire.osgibooter.UITestApplication.runApplication(UITestApplication.java:31)
at org.eclipse.tycho.surefire.osgibooter.AbstractUITestApplication.run(AbstractUITestApplication.java:115)
at org.eclipse.tycho.surefire.osgibooter.UITestApplication.start(UITestApplication.java:37)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
at org.eclipse.equinox.launcher.Main.run(Main.java:1515)
at org.eclipse.equinox.launcher.Main.main(Main.java:1488)

Answer 1

A virtual desktop must run. One can use Xvfb for this as described at http://www-01.ibm.com/support/docview.wss?uid=swg21421214. On Redhat one can use:
yum install xorg-x11-server-Xvfb
Xvfb :5 -screen 0 1280x1024x8 -fbdir /tmp &
export DISPLAY=:5
The number for the display can be chosen arbitrarily. In the Jenkins job the environment variable must be set as well (via set-env plugin).
For enabling this for all jobs a script as desribed here: https://superuser.com/questions/319040/proper-way-to-start-xvfb-on-startup-on-centos should be setup with chkconfig. Finally the environment variable DISPLAY should be made available by adding a shell script to /etc/profile.d/ which contains the sole line:
export DISPLAY=:5
During experimenting I set the default runlevel to 5 in /etc/inittab/ but I did no further research whether this is strictly necessary.