tramp + async-shell-command ignores shell-file-name

Question

If I locally call async-shell-command it takes the shell from shell-file-name (/bin/bash).

However if I use su or ssh via tramp to invoke a shell command remotely it always runs as /bin/sh. The default shell on the remote box is bash.

This is not the case if run an interactive M-x shell where the correct bash shell is always used, both remotely and locally.

My config looks like:

(setq explicit-shell-file-name "/bin/bash")
(setq shell-file-name explicit-shell-file-name)

I'm using emacs 25.3

Any ideas how to make bash the default shell when running shell commands via tramp?

Answer 1

tramp-handle-shell-command carries the comment

;; We cannot use `shell-file-name' and `shell-command-switch',
;; they are variables of the local host.

Instead, it uses the arguments tramp-remote-shell and tramp-remote-shell-args from the variable tramp-methods. You can override them by tweaking tramp-connection-properties, the Tramp manual discusses exactly the given case in the section Setting own connection related information:

(add-to-list 'tramp-connection-properties
             (list (regexp-quote "/ssh:[email protected]:")
                   "remote-shell" "/bin/ksh"))
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "/ssh:[email protected]:")
                   "remote-shell-login" '("-")))