Just in general, look up .ssh/config and configure it.

A lot of software uses ssh to do various things. You can pull a lot of neat tricks with SSH config coming in through a bastion on a non-standard port to a host machine into a shell executed in a docker container with the right .ssh/config, aliased to "machine", and the you can use anything that can run on SSH to "machine" with all that fancy configuration. Check your favorite editor; good odds it can edit files through that mess, or give you a remote directory explorer, or whatever.

Word of warning: using jump hosts shift your mindset towards building an internal network with lax security, the crunchy outside/soft tasty inside security antipattern.

(Yes you don't intend it at the start, but the realities of your later evaluations of where to invest effort security-wise will leave the internal network to rot since you won't think of the scenarios of how it would be compromised)

Isn't that typically already the mindset, since most people set up networks with non-routable (10, 192.168 etc) IP addresses?

It's a chicken-and-egg situation, yep. But the world seems to be moving towards zero trust networks, distaste towards complexity and opacity brought on by ambiguous rfc1918 addresses, and wide availability of ipv6.

Incidentally, I just filed a ticket because ProxyJump is not a known keyword in VScode’s SSH config autocomplete. It’s such a handy tool. Only landed in OpenSSH 7.3 in 2016 so it’s not that surprising it isn’t well known.

That `tmux` bit is clever. Wonder if you could do that in a `ForceCommand` or something like that so you don’t need to type that part either?

A combination of `RemoteCommand` and `RequestTTY` should do the trick:

    Host <host>
        ...
        RequestTTY yes
        RemoteCommand tty

The problem is that this will mess up your one-off command invocations of ssh, git ssh connections, etc:

    $ ssh <host> ls
    Cannot execute command-line and remote command.

However, we can use `Match` blocks to get around that! There are a thousand ways to skin this cat, but one way is to use an environment variable, here `t` for "tmux". Put this at the end of your config:

    Match exec "test ${t:-0} = 1"
        RequestTTY yes
        RemoteCommand tmux has-session && tmux attach-session || tmux

and the following Just Work, reattaching tmux sessions as necessary:

    $ t=1 ssh <host>
    $ ssh <host> ls

Nice. `Match exec` is one of my favorite things. It's too bad the command being passed to `ssh` (if there is one) isn't available as a `TOKEN` (as far as I can tell). That would put a bow on everything.

I simply have two configs for machines I ssh to often - one to the «normal shell» and one to a tmux instance with standard name.

(Not OP) I personally don't type my advanced commands, I alias them. So I would use "ssh-target" as my alias there.

Same -- and I comment them heavily, so when (like today per this thread) I learn more about said advanced options, I'm "forced" to update my "docs". Always be capturing your knowledge! :)