Não é possível obter informações de Buffer / Exibição de Quadro Virtual (Xvfb) com xdpyinfo

Question

Ubuntu Server 16.04 em execução no VirtualBox

Configuração

sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
sudo apt-get update
sudo apt-get install xvfb dbus-x11 google-chrome-stable

Teste

$xvfb-run -a --server-args='-screen 0, 1024x768x16' google-chrome -start-maximized http://example.com > /dev/null &

$ ps auxx | grep Xvfb
user   1355  1.2  1.6 174992 33808 ?        S    13:21   0:30 Xvfb :99 -screen 0, 1024x768x16 -nolisten tcp -auth /tmp/xvfb-run.adDyGd/Xauthority

$ cat /tmp/xvfb-run.adDyGd/Xauthority
user99MIT-MAGIC-COOKIE-1��gj��/�������auser@user:~$

Problema

$ xdpyinfo -display :99
No protocol specified
xdpyinfo:  unable to open display ":99".

• O que significa "Nenhum protocolo especificado"?
• O que poderia fazer com que o xdpyinfo falhasse aqui?

ATUALIZAÇÃO 16/05/2016

Iniciando o Xvfb manualmente e definindo o número de exibição antes de executar o chrome, funciona. No entanto xvfb-run não.

Xvfb manualmente

$ sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install xvfb dbus-x11 google-chrome-stable

$ Xvfb :99 -screen 0 1024x768x24 > /dev/null &

$ xdpyinfo -display :99
name of display:    :99
version number:    11.0
vendor string:    The X.Org Foundation
vendor release number:    11803000
X.Org version: 1.18.3
maximum request size:  16777212 bytes
motion buffer size:  256
bitmap unit, bit order, padding:    32, LSBFirst, 32
image byte order:    LSBFirst
number of supported pixmap formats:    6
supported pixmap formats:
    depth 1, bits_per_pixel 1, scanline_pad 32
    depth 4, bits_per_pixel 8, scanline_pad 32
    depth 8, bits_per_pixel 8, scanline_pad 32
    depth 16, bits_per_pixel 16, scanline_pad 32
    depth 24, bits_per_pixel 32, scanline_pad 32
    depth 32, bits_per_pixel 32, scanline_pad 32
keycode range:    minimum 8, maximum 255
focus:  PointerRoot
number of extensions:    25
    ...
default screen number:    0
number of screens:    1

screen #0:
  dimensions:    1024x768 pixels (260x195 millimeters)
  resolution:    100x100 dots per inch
  depths (6):    24, 1, 4, 8, 16, 32
  root window id:    0x25c
  depth of root window:    24 planes
  number of colormaps:    minimum 1, maximum 1
  default colormap:    0x20
  default number of colormap cells:    256
  preallocated pixels:    black 0, white 16777215
  options:    backing-store WHEN MAPPED, save-unders NO
  largest cursor:    1024x768
  current input event mask:    0x0
  number of visuals:    240
  default visual id:  0x21

$ export DISPLAY=:99 && google-chrome -start-maximized http://example.com > /dev/null &

$ ps auxx | grep 'chrome\|Xvfb' | grep -v grep
ubuntu   14843  0.0  0.4 193320 35308 pts/0    Sl   17:57   0:00 Xvfb :99 -screen 0 1024x768x24
ubuntu   14856  0.2  1.3 569044 108484 pts/0   Sl   17:58   0:01 /opt/google/chrome/chrome -start-maximized http://example.com
ubuntu   14868  0.0  0.6 358448 49424 pts/0    S    17:58   0:00 /opt/google/chrome/chrome --type=zygote
ubuntu   14869  0.0  0.1 142096  9596 pts/0    S    17:58   0:00 /opt/google/chrome/nacl_helper
ubuntu   14872  0.0  0.1 358448 11012 pts/0    S    17:58   0:00 /opt/google/chrome/chrome --type=zygote
ubuntu   14960  0.0  0.7 446888 64060 pts/0    Sl   17:58   0:00 /opt/google/chrome/chrome --type=gpu-process --channel=14856.0.2123468494 --window-depth=24 --supports-dual-gpus=false --gpu-driver-bug-workarounds=4,53 --disable-accelerated-video-decode --gpu-vendor-id=0x1013 --gpu-device-id=0x00b8 --gpu-driver-vendor --gpu-driver-version --v8-natives-passed-by-fd --v8-snapshot-passed-by-fd

com xvfb-run

$ xvfb-run -a --server-args='-screen 0, 1024x768x24' google-chrome -start-maximized http://example.com > /dev/null &

$ ps auxx | grep 'chrome\|Xvfb' | grep -v grep
ubuntu    1196  0.0  0.0   4508  1644 pts/0    S    18:15   0:00 /bin/sh /usr/bin/xvfb-run -a --server-args=-screen 0, 1024x768x24 google-chrome -start-maximized http://example.com
ubuntu    1208  0.0  0.4 193192 35572 pts/0    Sl   18:15   0:00 Xvfb :99 -screen 0, 1024x768x24 -nolisten tcp -auth /tmp/xvfb-run.8pPvAX/Xauthority
ubuntu    1213  0.4  1.3 619068 106576 pts/0   Sl   18:15   0:00 /opt/google/chrome/chrome -start-maximized http://example.com
ubuntu    1224  0.0  0.5 358448 47768 pts/0    S    18:15   0:00 /opt/google/chrome/chrome --type=zygote
ubuntu    1225  0.0  0.1 142128  9600 pts/0    S    18:15   0:00 /opt/google/chrome/nacl_helper
ubuntu    1228  0.0  0.1 358448 10492 pts/0    S    18:15   0:00 /opt/google/chrome/chrome --type=zygote
ubuntu    1440  0.0  0.7 738140 62828 pts/0    Sl   18:15   0:00 /opt/google/chrome/chrome --type=renderer --lang=en-US --enable-offline-auto-reload --enable-offline-auto-reload-visible-only --enable-pinch --num-raster-threads=1 --content-image-texture-target=3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553 --video-image-texture-target=3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553,3553 --disable-accelerated-video-decode --disable-webrtc-hw-encoding --disable-gpu-compositing --channel=1213.0.1322123415 --v8-natives-passed-by-fd --v8-snapshot-passed-by-fd

$ xdpyinfo -display :99
No protocol specified
xdpyinfo:  unable to open display ":99".

Observe a diferença no comando Xvfb que o xvfb-run usa:

Xvfb :99 -screen 0, 1024x768x24 -nolisten tcp -auth /tmp/xvfb-run.8pPvAX/Xauthority

No entanto, esse não é o problema, já que executá-lo sozinho e obter as informações de exibição funcionam bem.