使用systemd运行的Python脚本无法启动gedit

Question

I have the following Python script in /home/jack/Code/Service/main.py :

from subprocess import Popen

Popen(["/usr/bin/gedit"])

while True:
    pass

I am running it with this systemd service:

[Unit]
Description=Test

[Service]
Type=simple
Restart=no
User=jack
WorkingDirectory=/home/jack/Code/Service
ExecStart=/usr/bin/python3 main.py

[Install]
WantedBy=multi-user.target

When I run main.py from the command line with python3 main.py , it runs and gedit opens. When I start the systemd service and look at the logs, I see:

mars 10 11:19:55 Ubuntu-Tower systemd[1]: Started Test.
mars 10 11:19:55 Ubuntu-Tower python3[8827]: Unable to init server: Could not connect: Connection refused
mars 10 11:19:55 Ubuntu-Tower gedit[8835]: cannot open display: 

Note that the gedit process actually does appear in the system monitor when the service runs (and only disappears when I stop the service), so this really seems to be a GUI-specific problem.

What is going on, and how can I get the behavior I want?

Answer 1

To open a window in X11, the windows system of Linux and others, you must specify a display. Usually this is defined in the DISPLAY environment variable. In my case it is set to ":0.0". If this variable is not set, the program does not know where to draw the window:

marco$ DISPLAY= xeyes
Error: Can't open display:
marco$

Some programs allows you to specify the display via the -display parameter. This information alone is not enough: X11 incorporates an access control list of allowed clients that can connect to a specific server.

marco$ su - test
Password:
test$ env | grep DISPLAY
DISPLAY=:0.0
test$ xeyes
No protocol specified
Error: Can't open display: :0.0

xhost is the tool to manipulate the acl:

marco$ xhost +
access control disabled, clients can connect from any host
marco$ su - test
Password:
# disable X11 acl with xhost +
test:~$ xeyes
^C

In any case remember that the X11 server must be running to be able to open windows an you can incur in other kinds of errors if the server is not listening when the service is started (Unable to init server: Could not connect: Connection refused)