How to specify local shell for Fabric2/Paramiko/Invoke? - python-3.x

Question

When trying to create a fabric2.Connection, Paramiko tries to invoke a local /bin/bash command:
$ fab2 db-shell
Traceback (most recent call last):
File "/nix/store/m2iyj18cifr4a1rvpfgphg7kfgsf2pj2-python3.9-fabric2-2.7.1/bin/.fab2-wrapped", line 9, in <module>
sys.exit(program.run())
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/program.py", line 384, in run
self.execute()
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/program.py", line 566, in execute
executor.execute(*self.tasks)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/executor.py", line 129, in execute
result = call.task(*args, **call.kwargs)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/tasks.py", line 127, in __call__
result = self.body(*args, **kwargs)
File "/home/username/project/fabfile.py", line 645, in db_shell
bastion_connection().run(
File "/home/username/project/fabfile_utils.py", line 141, in bastion_connection
conn = Connection(
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/fabric2/connection.py", line 403, in __init__
self.ssh_config = self.config.base_ssh_config.lookup(host)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/paramiko/config.py", line 223, in lookup
options = self._lookup(hostname=hostname)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/paramiko/config.py", line 250, in _lookup
or self._does_match(
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/paramiko/config.py", line 389, in _does_match
passed = invoke.run(exec_cmd, hide="stdout", warn=True).ok
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/__init__.py", line 48, in run
return Context().run(command, **kwargs)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/context.py", line 95, in run
return self._run(runner, command, **kwargs)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/context.py", line 102, in _run
return runner.run(command, **kwargs)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/runners.py", line 380, in run
return self._run_body(command, **kwargs)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/runners.py", line 431, in _run_body
self.start(command, self.opts["shell"], self.env)
File "/nix/store/20k85mfdkbrj5w1pq0d7dzagygfip70h-python3-3.9.13-env/lib/python3.9/site-packages/invoke/runners.py", line 1291, in start
self.process = Popen(
File "/nix/store/0zzvjh5gnz0ny7ckilzyn9hmg5lypszf-python3-3.9.13/lib/python3.9/subprocess.py", line 951, in __init__
self._execute_child(args, executable, preexec_fn, close_fds,
File "/nix/store/0zzvjh5gnz0ny7ckilzyn9hmg5lypszf-python3-3.9.13/lib/python3.9/subprocess.py", line 1821, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: '/bin/bash'
I've not been able to find anything in the docs about this yet.
I'm running fabric2==2.7.1, invoke==1.6.0, and paramiko==2.8.0 on NixOS stable 22.11.

Answer 1

Invoke currently defaults to /bin/bash, which is a known issue, since operating systems like Alpine and NixOS don't have that path. Fortunately we can specify a command in $PATH rather than manually looking it up, so adding the following to the Connection call does the trick: config=invoke.Config(overrides={"shell": "bash"}).