[Bug 1071264] [NEW] sshd cannot be remotely restarted from an ssh session

[urilabob]

Public bug reported:

Maybe this is a request for enhancement... but it works in Fedora, so
I'm guessing it's intended to work in ubuntu 8^).

In Fedora, I can ssh into a remote host,  issue 'systemctl restart
sshd.service' (or in earlier versions, 'service sshd restart'), and the
result is that sshd restarts - in particular, re-reading its config
file. Not only that, but the ssh session I am logged in on is preserved.

In ubuntu, the equivalent actions - 'service ssh restart',
'/etc/init.d/ssh restart' and 'restart ssh' all fail with "error: Bind
to port 22 on 0.0.0.0 failed: Address already in use." I guess that is
because my current ssh session prevents the current instance of sshd
shutting down. But somehow Fedora manages it...

Steps to recreate:
1. ssh to remote server
2. sudo edit /etc/ssh/sshd_config, or other relevant file
3. sudo restart ssh

Actual result:
error: Bind to port 22 on 0.0.0.0 failed: Address already in use.
(and sshd fails to restart)

Expected result:
sshd restarts (preferably with running ssh sessions intact, but even killing the running ssh sessions would be preferable to current state).

The bottom line is that minor sshd reconfigurations on remote Fedora
systems require only a restart of the sshd daemon. On ubuntu, they
require a full reboot (which you may want to keep to a minimum on a
remote system that you don't have physical access to). I realise that
preserving the running ssh sessions over an sshd restart might be
complex (and even undesirable, because it could lead to security issues
with sessions still running with configurations that are intended to be
fixed). But even having the sshd restart kill the connections of the
current running sessions (so that it would be necessary to log in again)
would be better than the current setup.

Apologies if this has already been discussed - googling and ubuntu
searches failed to turn it up.

System: 
Description:	Ubuntu 10.04.4 LTS
Release:	10.04

Package:
openssh-server:
  Installed: 1:5.3p1-3ubuntu7
  Candidate: 1:5.3p1-3ubuntu7
  Version table:
 *** 1:5.3p1-3ubuntu7 0
        500 http://archive.ubuntu.com/ubuntu/ lucid-updates/main Packages
        100 /var/lib/dpkg/status
     1:5.3p1-3ubuntu3 0
        500 http://archive.ubuntu.com/ubuntu/ lucid/main Packages

** Affects: openssh (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1071264

Title:
  sshd cannot be remotely restarted from an ssh session

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