Error while using selenium over Xvfb (headless)

I have Ubuntu machine running Xvfb and Selenium server standalone (v2.20.0).
I'm trying to run my test by phpunit with selenium.
I can see by the log its start session and trying to open google chrome but the browser doesn't open and its stuck in this mode

Code:


Mar 21, 2012 9:27:37 AM org.openqa.grid.selenium.GridLauncher main
INFO: Launching a standalone server
0 [main] INFO org.openqa.selenium.server.SeleniumServer - Java: Sun Microsystems Inc. 20.0-b12
0 [main] INFO org.openqa.selenium.server.SeleniumServer - OS: Linux 3.2.0-8-generic-pae i386
7 [main] INFO org.openqa.selenium.server.SeleniumServer - v2.20.0, with Core v2.20.0. Built from revision 16008
178 [main] INFO org.openqa.selenium.server.SeleniumServer - RemoteWebDriver instances should connect to: 127.0.0.1:4444/wd/hub
179 [main] INFO org.openqa.jetty.http.HttpServer - Version Jetty/5.1.x
180 [main] INFO org.openqa.jetty.util.Container - Started HttpContext[/selenium-server/driver,/selenium-server/driver]
180 [main] INFO org.openqa.jetty.util.Container - Started HttpContext[/selenium-server,/selenium-server]
181 [main] INFO org.openqa.jetty.util.Container - Started HttpContext[/,/]
43119 [main] INFO org.openqa.jetty.util.Container - Started org.openqa.jetty.jetty.servlet.ServletHandler@1b3f8f6
43120 [main] INFO org.openqa.jetty.util.Container - Started HttpContext[/wd,/wd]
43127 [main] INFO org.openqa.jetty.http.SocketListener - Started SocketListener on 0.0.0.0:4444
43127 [main] INFO org.openqa.jetty.util.Container - Started org.openqa.jetty.jetty.Server@1006d75
108588 [SocketListener0-0] INFO org.openqa.jetty.util.Credential - Checking Resource aliases
09:29:26.205 INFO - Command request: getNewBrowserSession[googlechrome, localhost:8080/] on session null
09:29:26.208 INFO - creating new remote session
09:29:26.227 WARN - Caution: '/usr/bin/google-chrome': file is a script file, not a real executable.  The browser environment is no longer fully under RC control
09:29:26.230 INFO - Allocated session 20de5dfc1d1c492cba1e1cd26234cb14 for localhost:8080/, launching...
09:29:26.231 INFO - Launching Google Chrome...



Same going with firefox.


And if I try to run firefox/chrome by command Its work.
Why can't I run browsers from Selenium?