The absence of `/usr/bin/python` will defeat `pyenv` to find an appropriate system python binary, which will in turn prevent `x11docker` from starting properly.

[hongyi-zhao]

I'm currently using pyenv as the Python version manager. And it seems that this will invalidate the python version judgment part of x11docker:

  # check python version
  Pythonbin="$(command -v python)"
  [ -z "$Pythonbin" ] && Pythonbin="$(command -v python3)"
  [ -z "$Pythonbin" ] && Pythonbin="$(command -v python2)"

For more details, see my tests below:

werner@X10DAi-00:~$ command -v python
/home/werner/.pyenv/shims/python
werner@X10DAi-00:~$ command -v python3
/home/werner/.pyenv/shims/python3
werner@X10DAi-00:~$ command -v python2
/home/werner/.pyenv/shims/python2

So, I think some code logic enhancements should be needed to handle this situation.

Regards, HZ

[mviereck]

Thank you for pointing on this. In fact, it doesn't matter for x11docker which python version is used. The check is only needed to find some arbitrary python binary.

[hongyi-zhao]

But in the pyenv case, as I've reported above, the following problem will be triggered by x11docker:

werner@X10DAi-00:~$ command -v python
/home/werner/.pyenv/shims/python
werner@X10DAi-00:~$ /home/werner/.pyenv/shims/python
pyenv: python: command not found

The `python' command exists in these Python versions:
  2.7.18
  3.10.1
  3.5.6
  3.6.10
  3.7.7
  3.8.3
  3.8.3/envs/socks5-haproxy
  3.8.3/envs/wannierberri
  3.9.1
  3.9.1/envs/aiida
  3.9.1/envs/datasci
  3.9.2
  3.9.2/envs/firedm
  3.9.7
  3.9.7/envs/kwant
  aiida
  datasci
  firedm
  kwant
  socks5-haproxy
  wannierberri

Note: See 'pyenv help global' for tips on allowing both
      python2 and python3 to be found.

[mviereck]

But how would one start python if the python command is invalid?

Edit: Currently I suspect a wrong pyenv setup.

[hongyi-zhao]

Edit: Currently I suspect a wrong pyenv setup.

Why? I've been using pyenv for a long time, and haven't seen anyone call the behavior described here a bug.

[mviereck]

Normal pathes are /usr/bin/python or /usr/bin/python3. The path /home/werner/.pyenv/shims/python indicates that it is provided by pyenv. But calling this command leads to an error. It should run your desired python version chosen with pyenv.

Edit: In a nutshell: On your system calling the command python leads to an error. This is independent from x11docker.

[hongyi-zhao]

Wonderful analysis. The problem is caused by the absence of /usr/bin/python on my system:

$ ls /usr/bin/python
ls: cannot access '/usr/bin/python': No such file or directory

To summarize: The absence of /usr/bin/python will defeat pyenv to find an appropriate system python binary, which will in turn prevent x11docker from starting properly. So, the fix is as follows:

$ apt-file search -x /usr/bin/python$
python-is-python2: /usr/bin/python        
python-is-python3: /usr/bin/python
$ sudo apt install -y python-is-python3
$ realpath -e /usr/bin/python
/usr/bin/python3.8
$ which python
/home/werner/.pyenv/shims/python
$ python --version
Python 3.8.10