openssh unix dev - Sep 2016 - possibility of a RemoteCommand option in the ssh config file

Hi,

About one year ago, someone (Simon Zack) asked about a RemoteCommand
option.

His question did not encounter a large amount of answers, maybe because
Simon himself did not answer to a question from Darren Tucker about his use
case ? However, I think I have a use case pretty close to Simon's one:

Let's imagine a host named 'lxc.host.example.org', hosting many LXC
containers named '<cont>.lxc.host.example.org'.
With a RemoteCommand option, working pretty much the same as the
ProxyCommand one, we could write something like:

$ cat ~/.ssh/config
Host host.lxc.example.org
    RequestTTY force

Host *.host.lxc.example.org
    Hostname host.lxc.example.org
    RemoteCommand lxc-attach -n %h --

That way, we would be able to attach to containers, without the need to run
sshd inside each container, by running:

$ ssh mycontainer.host.lxc.example.org

A bit of difference with the ProxyCommand behaviour, though: the %h macro
should expand to the host that was requested on the cli; not the one
specified with Hostname.

I know I can specify the command on the cli, or even make an alias, but it
would introduce an interface difference for the end-user between regular
hosts and lxc containers.

Any opinion ?

Kind regards,
r?mi

Paulmier wrote:
> Hi,
>
> About one year ago, someone (Simon Zack) asked about a RemoteCommand
> option.
>
> His question did not encounter a large amount of answers, maybe because
> Simon himself did not answer to a question from Darren Tucker about his use
> case ? However, I think I have a use case pretty close to Simon's one:
>
> Let's imagine a host named 'lxc.host.example.org', hosting many
LXC
> containers named '<cont>.lxc.host.example.org'.
> With a RemoteCommand option, working pretty much the same as the
> ProxyCommand one, we could write something like:
>
> $ cat ~/.ssh/config
> Host host.lxc.example.org
>      RequestTTY force
>
> Host *.host.lxc.example.org
>      Hostname host.lxc.example.org
>      RemoteCommand lxc-attach -n %h --
>
> That way, we would be able to attach to containers, without the need to run
> sshd inside each container, by running:
>
> $ ssh mycontainer.host.lxc.example.org
>
> A bit of difference with the ProxyCommand behaviour, though: the %h macro
> should expand to the host that was requested on the cli; not the one
> specified with Hostname.
You should use %n for that.

I like your use case, although you could the same thing (in a more 
convoluted configuration)
using ForceCommand on the ssh key at the authorized_keys of

host.lxc.example.org


Cheers