PyVirtualDisplay

pyvirtualdisplay is a python wrapper for Xvfb, Xephyr and Xvnc programs. They all use the X Window System (not Windows, not macOS) The selected program should be installed first so that it can be started without a path, otherwise pyvirtualdisplay will not find the program.

Links:

• home: https://github.com/ponty/pyvirtualdisplay
• PYPI: https://pypi.python.org/pypi/pyvirtualdisplay

Features:

• python wrapper
• supported python versions: 3.6, 3.7, 3.8, 3.9, 3.10, 3.11, 3.12
• back-ends: Xvfb, Xephyr and Xvnc

Possible applications:

• headless run
• GUI testing
• automatic GUI screenshot

Installation

install the program:

$ python3 -m pip install pyvirtualdisplay

optional: Pillow should be installed for smartdisplay submodule:

$ python3 -m pip install pillow

optional: EasyProcess should be installed for some examples:

$ python3 -m pip install EasyProcess

optional: xmessage and gnumeric should be installed for some examples.

On Ubuntu 22.04:

$ sudo apt install x11-utils gnumeric

If 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 22.04:

$ sudo apt-get install xvfb xserver-xephyr tigervnc-standalone-server x11-utils gnumeric
$ python3 -m pip install pyvirtualdisplay pillow EasyProcess

Usage

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()) # False

Controlling the display with start() and stop() methods (not recommended):

from pyvirtualdisplay import Display
disp = Display()
disp.start()
# display is active
disp.stop()
# display is stopped

After 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.headless

If 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.vncserver

Check 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.lowres

Image:

Screenshot

…

Run it:

$ python3 -m pyvirtualdisplay.examples.screenshot

Image:

Nested Xephyr

…

Run it:

$ python3 -m pyvirtualdisplay.examples.nested

Image:

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.

Mouse cursor

The cursor can be disabled in Xvfb using an extra argument which is passed directly to Xvfb:

with Display(backend="xvfb", extra_args=["-nocursor"]):
    ...

Based on Xvfb help:

...
-nocursor              disable the cursor
...

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.

…

Run it:

$ python3 -m pyvirtualdisplay.examples.threadsafe

Images:

Hierarchy