I am trying to run a mobile web test using appium on Centos 6 **headless linux** but I am keep getting this error:

```
"info: [CHROMEDRIVER STDERR] No protocol specified

info: Responding to client with error: {"status":13,"value":{"message":"An unknown server-side error occurred while processing the command.","origValue":"**unknown error: an X display is required for keycode conversions, consider using Xvfb\n**  (Session info: chrome=webview)\n  (Driver info:chromedriver=2.9.248316,platform=Linux 2.6.32-042stab088.4x86_64)"},"sessionId":"8563fbe5972f3ba87673c7a082d49d22"}
POST /wd/hub/session/8563fbe5972f3ba87673c7a082d49d22/element/0.06753459526225924-1/value 500 1927ms - 395b

debug: Appium request initiated at /wd/hub/session/8563fbe5972f3ba87673c7a082d49d22

debug: Request received with params: {}

info: Shutting down appium session..."

```

It opens up the chrome browser and navigates to the given url. After that it tries `sendKeys` to the username field and then it fails.