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Are there any alternative SSH servers other than SSHD?

One that is not SSH based? Ideally one that can be installed from offical Debian repository, that listens on a port other than port 22. (To avoid conflicts with ssh from the beginning.)

Must be secure as ssh (authentication, encryption).

Purpose:
Emergency login if SSHD does not come up after reboot.

Original issue:
No non-SSH based out of band server management for a server available.

Non-solutions:
Mosh looks nice, but it is also using ssh in background, so of no help for this use case.

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    Why are you afraid that sshd might not come up? Has it happened before? What machine is that, maybe some kind of an unstable development board? I think that it's worth finding a reason why sshd does not come up instead of looking for alternatives. – Arkadiusz Drabczyk Mar 10 '15 at 19:17
  • what do you mean by "non ssh-based"? ssh is a protocol rather than an implementation; do you want to avoid the default implementation OpenSSH? or do you want to avoid the protocol altogether (while looking for the same feature-set)? – umläute Mar 10 '15 at 19:54
  • If the questioner's experience is anything like my own "sshd does not come up after a reboot" translates to things like "forgot to enable the socket unit before rebooting" or "accidentally removed the wrong package with aptitude, and rebooted". Unlike the questioner, my experience has always included remote kernel virtual terminal access to fall back upon. The questioner's question appears to be the What if I accidentally disable ssh and I have no remote vty access and there's no handy WWW-based server management UI? form of this oft-asked question. – JdeBP Mar 10 '15 at 20:00
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    OpenSSH is very well maintained. I would trust its security over that of OpenSSL or Dropbear. If your issue is with ssh keys, there are probably ways to configure sshd_config to allow password access for select accounts (not root!), which could present a decently secure back door, especially if you have something like Fail2ban to limit password attempts. – Adam Katz Mar 10 '15 at 21:05
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Drop bear might work. It does use the SSH protocol, but it doesn't share a code base with OpenSSH, so it probably won't crash in the same circumstances. I'm pretty sure you can configure both OpenSSH and Drop Bear to listen on ports other than TCP 22.

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The obvious answer for "remote shell" used to be telnet (urgh!).

It seems that these days there is an SSL-enabled version of telnet, readily available on debian as:

 telnetd-ssl

(I have to admit though, that I don't know anything about it as I've always been happy with ssh; given the bad reputation of telnet (mainly based on it's non-encrypted nature) I wouldn't even recommend it (even though this version obviously has encryption - just mentioning for the sake of completeness)

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