mjhjmtu

I believe this should be simple but I can't get it to work properly.

These are the commands I can run on command line:

cd /home/debian/ap

# Start a virtualenv
source venv-ap/bin/activate

# This needs to happen inside the virtualenv and takes ~20 seconds
crossbar start

# Outside the virtualenv, perhaps in a different command line window
python3 /home/debian/myscript.py

These commands have to be done in this order. Due to the virtualenv, the non-executable for crossbar, and the separate python script afterwards, I haven't been able to figure out the best way to get this to work. My current work-in-progress:

[Unit]
Description=Start CB
After=network.target

[Service]
Type=simple
User=debian
ExecStartPre=source /home/debian/ap/venv-ap/bin/activate
ExecStart=cd /home/debian/ap/ && crossbar start
Restart=always

[Install]
WantedBy=multi-user.target

This doesn't work because source is a shell command, so systemd's ExecStart= or ExecStartPre= won't understand them directly... (BTW, the same is true for cd and the &&.)

You could achieve that by running a shell explicitly and running all your commands together there:

ExecStart=/bin/sh -c 'cd /home/debian/ap/ && source venv-ap/bin/activate && crossbar start'

But a better approach is, instead of sourcing the "activate" script, to use the python executable in the bin/ of your virtualenv directly.

If you look at virtualenv's usage document, you'll notice it says:

ENV/bin is created, where executables live - noticeably a new python. Thus running a script with #! /path/to/ENV/bin/python would run that script under this virtualenv’s python.

In other words, assuming crossbar is the Python script you want to run that requires the venv-ap virtualenv, simply begin crossbar with:

#!/home/debian/ap/venv-ap/bin/python

And it will automatically use the virtualenv whenever invoked.

Also possible, invoking the Python interpreter from the virtualenv directly, with:

ExecStart=/home/debian/ap/venv-ap/bin/python /path/to/crossbar start

(Also, regarding running in a specific directory, setting WorkingDirectory=/home/debian/ap is better than using a cd command. You don't need a shell that way, and systemd can do better error handling for you.)