Shell used for the run `commands`

[un-def]

Currently, which shell is used to execute commands depends on the image property:

• if image is not specified, the dstackai/base image is used, and the shell is /bin/bash
• otherwise, the shell is /bin/sh

dstack/src/dstack/_internal/server/services/jobs/configurators/base.py

Lines 138 to 143 in 99a88d3

	elif self.run_spec.configuration.image is None: # dstackai/base
	entrypoint = ["/bin/bash", "-i", "-c"]
	commands = [_join_shell_commands(self._shell_commands())]
	elif self._shell_commands(): # custom docker image with shell commands
	entrypoint = ["/bin/sh", "-i", "-c"]
	commands = [_join_shell_commands(self._shell_commands())]

This should be at least documented.

Plan

• (required) document the current behavior
• (optional but nice to have) add a new optional property shell keeping the current logic for the default value (bash for default dstackai/base images, sh for other images)
• (optional) make dstackai/base images work with sh, make sh the default shell for all images