Not using "expect fork" of course would mean that ssh would be reported as
running before it was actually listening for connections.

On Mon, Dec 13, 2010 at 10:13 PM, Clint Byrum <email address hidden> wrote:

> In looking at the code in OpenSSH, the -D flag only affects this portion
> of sshd.c, around line 1740:
>
>
>    /*
>     * If not in debugging mode, and not started from inetd, disconnect
>     * from the controlling terminal, and fork.  The original process
>     * exits.
>     */
>    if (!(debug_flag || inetd_flag || no_daemon_flag)) {
> #ifdef TIOCNOTTY
>        int fd;
> #endif /* TIOCNOTTY */
>        if (daemon(0, 0) < 0)
>            fatal("daemon() failed: %.200s", strerror(errno));
>
>        /* Disconnect from the controlling tty. */
> #ifdef TIOCNOTTY
>        fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
>        if (fd >= 0) {
>            (void) ioctl(fd, TIOCNOTTY, NULL);
>            close(fd);
>        }
> #endif /* TIOCNOTTY */
>    }
>
> "no_daemon_flag" isn't used anywhere else in the code.
>
> Consequently, this code is why the daemon forks on reload, because it
> re-execs itself, causing this code to be hit. When run with -D, there's
> no call to daemon.
>
> The call to daemon should only chdir to / and close stdin/stdout/stderr,
> redirecting them to /dev/null. Given that upstart will already have done
> that, this is a non issue. The code then ioctl's on stdin to get rid of
> the controlling TTY, which also has no effect when run via upstart since
> it is connected to /dev/null. I believe this would change the behavior
> if we were using console owner, and sshd would exit on control-C in
> console if one was using that, but we're not going to do that, nor would
> be a reason to do that for sshd.
>
> I tested this on natty and maverick, killing the daemon in various ways,
> making sure that user sessions stay alive, and that reloads keep track
> of the daemon. I'm confident that this change is safe and will not cause
> any operational issues with openssh-server.
>
> I've submitted a merge proposal adding -D and dropping expect fork,
> which would fix this bug.
>
> ** Changed in: openssh (Ubuntu)
>     Assignee: (unassigned) => Clint Byrum (clint-fewbar)
>
> --
> You received this bug notification because you are a member of Upstart
> Developers, which is subscribed to upstart .
> https://bugs.launchpad.net/bugs/687535
>
> Title:
>  upstart loses track of ssh daemon after reload ssh
>
> Status in Upstart:
>  New
> Status in “openssh” package in Ubuntu:
>  Confirmed
> Status in “openssh” source package in Lucid:
>  Confirmed
> Status in “openssh” source package in Maverick:
>  Confirmed
>
> Bug description:
>  When sshd gets a signal 1 for reload, it forks a new process and ditches
> the old. This causes upstart to believe that ssh has crashed, and loses
> track of it. A second reload (or any other initctl operation on ssh) will
> thus say:
>
> reload: Unknown instance:
>
> There would be 2 ways to fix this:
> 1.  Don't have ssh fork on relod, but keep the same pid
> 2. Use a different mechanism in upstart to keep track of ssh. Maybe a pid
> file? Just tracking children of the exited ssh won't work, or it might
> accidentally track a particular session rather than the master, if somebody
> just happens to log in close to reload time.
>
>
> # lsb_release -rd
> Description:    Ubuntu 10.04.1 LTS
> Release:        10.04
>
> # dpkg -l openssh-server | cat
> Desired=Unknown/Install/Remove/Purge/Hold
> |
> Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
> |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
> ||/ Name                                        Version
>                                Description
>
> +++-===========================================-==========================================================-=================================================================
> ii  openssh-server                              1:5.3p1-3ubuntu4
>                                 secure shell (SSH) server, for secure access
> from remote machines
>
> # dpkg -l upstart
> Desired=Unknown/Install/Remove/Purge/Hold
> |
> Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
> |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
> ||/ Name           Version        Description
>
> +++-==============-==============-============================================
> ii  upstart        0.6.5-7        event-based init daemon
>
>
>