SSH stands for Secure SHell and is a protocol to logon to a terminal shell via network.
You need to have an SSHd (or Secure SHell Daemon i.e a background service) running to accept and facilitate connections.
Systemd is a suite of services and tools that manage a Linux system, like a init system, service management, handing run levels, socket management, logging etc and gives the user tools like systemctl, journalctl, bootctl, basically anything ending with ctl is conventionally a systemd tool for users to manage their systems with.
Get it? Got it? Good.
systemd.autossh is an embedded ssh client in systemd that tries to help in reestablishing dropping connections. It does not actually start an SSHd (the actual service that facilitates connections) and is embedded for convenience to minimize frustrations with dropping connections.
You are talking about autossh, which is a completely different third-party SSH client tool that you have to install separately (as the link you shared describes) to have persistent SSH client connections and has nothing to do with systemd other than that you can start it as a systemd service (like any other third-party service).
OP is talking about systemd-ssh-generator, which is described here by Lennart Poettering (author of systemd) as working exactly as OP described it.
Given that it helps with ssh client connections and sshd is, basically, a server—yes. And even then, I imagine it doesn’t actually do anything if there’s no ssh connection.
Op is a bit confused, but here’s a primer first:
SSH stands for Secure SHell and is a protocol to logon to a terminal shell via network.
You need to have an SSHd (or Secure SHell Daemon i.e a background service) running to accept and facilitate connections.
Systemd is a suite of services and tools that manage a Linux system, like a init system, service management, handing run levels, socket management, logging etc and gives the user tools like systemctl, journalctl, bootctl, basically anything ending with ctl is conventionally a systemd tool for users to manage their systems with.
Get it? Got it? Good.
systemd.autossh is an embedded ssh client in systemd that tries to help in reestablishing dropping connections. It does not actually start an SSHd (the actual service that facilitates connections) and is embedded for convenience to minimize frustrations with dropping connections.
You can read about it here.
*defeatedly puts away torch and pitchfork
*kicks dirt
Shucks I never get to be mad about systemd!
Every day I wake up and think to myself “today is the day I will form a strong opinion about systemd” but it never happens.
Heya thanks so much for that explanation, took a couple read throughs and some thinking but I think I get it!
The time ans thought you put into that are much appreciated and so emblematic of the awesome nature of the linux world.
Thanks again!
No, it seems you are a bit confused.
You are talking about autossh, which is a completely different third-party SSH client tool that you have to install separately (as the link you shared describes) to have persistent SSH client connections and has nothing to do with systemd other than that you can start it as a systemd service (like any other third-party service).
OP is talking about systemd-ssh-generator, which is described here by Lennart Poettering (author of systemd) as working exactly as OP described it.
So systemd.autossh is running even if sshd.service is disabled?
Given that it helps with ssh client connections and sshd is, basically, a server—yes. And even then, I imagine it doesn’t actually do anything if there’s no ssh connection.