Oops... It turned out that my regular user (not root) started sshd with that port number. and since only root allowed to open "high" ports, the connection got terminated.
1. why did sshd / ubuntu allowed the regular user to even start the service, when it's clear no connections will be received? 2. can't the second sshd instance detect such a port collision, and warn about it? mcas, thanks for helping. ** Changed in: openssh (Ubuntu) Status: Incomplete => Invalid -- openssh-server is unable to receive connections on some ports https://bugs.launchpad.net/bugs/251620 You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to openssh in ubuntu. -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs