I hope you do not mind me pushing this:
> MC FAQ:
>> 6.6 When I use Ctrl-O I don't get a subshell. How do I fix this?
>> Only bash, tcsh and zsh can be used as subshell. Use one of those
>> shells as your default shell, and it will be used as subshell in GNU
>> Midnight Commander.
> What is the reason for that? I use BusyBox ash on an embedded platform
> (DSL/LAN/WLAN router) and would like to have a Ctrl-O subshell. What
> would be technically required from a candidate shell in order to make it
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