pyvirtualdisplay is a python wrapper for Xvfb, Xephyr and Xvnc
Links:
Features:
- python wrapper
- supported python versions: 3.6, 3.7, 3.8, 3.9, 3.10, 3.11
- back-ends: Xvfb, Xephyr and Xvnc
Possible applications:
- headless run
- GUI testing
- automatic GUI screenshot
Installation
install the program:
$ python3 -m pip install pyvirtualdisplayoptional: Pillow should be installed for smartdisplay submodule:
$ python3 -m pip install pillowoptional: EasyProcess should be installed for some examples:
$ python3 -m pip install EasyProcessoptional: xmessage and gnumeric should be installed for some examples.
On Ubuntu 20.04:
$ sudo apt install x11-utils gnumericIf you get this error message on Linux then your Pillow version is old.
ImportError: ImageGrab is macOS and Windows only
Install all dependencies and backends on Ubuntu 20.04:
$ sudo apt-get install xvfb xserver-xephyr tigervnc-standalone-server x11-utils gnumeric
$ python3 -m pip install pyvirtualdisplay pillow EasyProcessUsage
Controlling the display with context manager:
from pyvirtualdisplay import Display
with Display() as disp:
# display is active
print(disp.is_alive()) # True
# display is stopped
print(disp.is_alive()) # FalseControlling the display with start() and stop() methods (not recommended):
from pyvirtualdisplay import Display
disp = Display()
disp.start()
# display is active
disp.stop()
# display is stoppedAfter Xvfb display is activated "DISPLAY" environment variable is set for Xvfb.
(e.g. os.environ["DISPLAY"] = :1)
After Xvfb display is stopped start() and stop() are not allowed to be called again, "DISPLAY" environment variable is restored to its original value.
Selecting Xvfb backend:
disp=Display()
# or
disp=Display(visible=False)
# or
disp=Display(backend="xvfb")Selecting Xephyr backend:
disp=Display(visible=True)
# or
disp=Display(backend="xephyr")Selecting Xvnc backend:
disp=Display(backend="xvnc")Setting display size:
disp=Display(size=(100, 60))Setting display color depth:
disp=Display(color_depth=24)Headless run
A messagebox is displayed on a hidden display.
# pyvirtualdisplay/examples/headless.py
"Start Xvfb server. Open xmessage window."
from easyprocess import EasyProcess
from pyvirtualdisplay import Display
with Display(visible=False, size=(100, 60)) as disp:
with EasyProcess(["xmessage", "hello"]) as proc:
proc.wait()Run it:
$ python3 -m pyvirtualdisplay.examples.headlessIf visible=True then a nested Xephyr window opens and the GUI can be controlled.
vncserver
The same as headless example, but it can be controlled with a VNC client.
# pyvirtualdisplay/examples/vncserver.py
"Start virtual VNC server. Connect with: vncviewer localhost:5904"
from easyprocess import EasyProcess
from pyvirtualdisplay import Display
with Display(backend="xvnc", size=(100, 60), rfbport=5904) as disp:
with EasyProcess(["xmessage", "hello"]) as proc:
proc.wait()Run it:
$ python3 -m pyvirtualdisplay.examples.vncserverCheck it with vncviewer:
$ vncviewer localhost:5904
GUI Test
# pyvirtualdisplay/examples/lowres.py
"Testing gnumeric on low resolution."
from easyprocess import EasyProcess
from pyvirtualdisplay import Display
# start Xephyr
with Display(visible=True, size=(320, 240)) as disp:
# start Gnumeric
with EasyProcess(["gnumeric"]) as proc:
proc.wait()Run it:
$ python3 -m pyvirtualdisplay.examples.lowresImage:
Screenshot
# pyvirtualdisplay/examples/screenshot.py
"Create screenshot of xmessage in background using 'smartdisplay' submodule"
from easyprocess import EasyProcess
from pyvirtualdisplay.smartdisplay import SmartDisplay
# 'SmartDisplay' instead of 'Display'
# It has 'waitgrab()' method.
# It has more dependencies than Display.
with SmartDisplay() as disp:
with EasyProcess(["xmessage", "hello"]):
# wait until something is displayed on the virtual display (polling method)
# and then take a fullscreen screenshot
# and then crop it. Background is black.
img = disp.waitgrab()
img.save("xmessage.png")Run it:
$ python3 -m pyvirtualdisplay.examples.screenshotImage:
Nested Xephyr
# pyvirtualdisplay/examples/nested.py
"Nested Xephyr servers"
from easyprocess import EasyProcess
from pyvirtualdisplay import Display
with Display(visible=True, size=(220, 180), bgcolor="black"):
with Display(visible=True, size=(200, 160), bgcolor="white"):
with Display(visible=True, size=(180, 140), bgcolor="black"):
with Display(visible=True, size=(160, 120), bgcolor="white"):
with Display(visible=True, size=(140, 100), bgcolor="black"):
with Display(visible=True, size=(120, 80), bgcolor="white"):
with Display(visible=True, size=(100, 60), bgcolor="black"):
with EasyProcess(["xmessage", "hello"]) as proc:
proc.wait()Run it:
$ python3 -m pyvirtualdisplay.examples.nestedImage:
xauth
Some programs require a functional Xauthority file. PyVirtualDisplay can
generate one and set the appropriate environment variables if you pass
use_xauth=True to the Display constructor. Note however that this
feature needs xauth installed, otherwise a
pyvirtualdisplay.xauth.NotFoundError is raised.
Concurrency
If more X servers are started at the same time then there is race for free display numbers.
"Recent X servers as of version 1.13 (Xvfb, too) support the -displayfd command line option: It will make the X server choose the display itself" https://stackoverflow.com/questions/2520704/find-a-free-x11-display-number/
Version 1.13 was released in 2012: https://www.x.org/releases/individual/xserver/
First help text is checked (e.g. Xvfb -help) to find if -displayfd flag is available.
If -displayfd flag is available then it is used to choose the display number.
If not then a free display number is generated and there are 10 retries by default
which should be enough for starting 10 X servers at the same time.
displayfd usage is disabled on macOS because it doesn't work with XQuartz-2.7.11, always 0 is returned.
Thread safety
All previous examples are not thread-safe, because pyvirtualdisplay replaces $DISPLAY environment variable in global os.environ in start() and sets back to original value in stop().
To make it thread-safe you have to manage the $DISPLAY variable.
Set manage_global_env to False in constructor.
# pyvirtualdisplay/examples/threadsafe.py
"Start Xvfb server and open xmessage window. Thread safe."
import threading
from easyprocess import EasyProcess
from pyvirtualdisplay.smartdisplay import SmartDisplay
def thread_function(index):
# manage_global_env=False is thread safe
with SmartDisplay(manage_global_env=False) as disp:
cmd = ["xmessage", str(index)]
# disp.new_display_var should be used for new processes
# disp.env() copies global os.environ and adds disp.new_display_var
with EasyProcess(cmd, env=disp.env()):
img = disp.waitgrab()
img.save("xmessage{}.png".format(index))
t1 = threading.Thread(target=thread_function, args=(1,))
t2 = threading.Thread(target=thread_function, args=(2,))
t1.start()
t2.start()
t1.join()
t2.join()Run it:
$ python3 -m pyvirtualdisplay.examples.threadsafeImages:
