I run an Openssh sshd service from Cygwin. When an RSA connection is established:

$ ssh Administrator@ZETA

Last login: Wed May 11 13:58:50 2016 from

-- there is no error message.

However, when I use an inline command:

$ ssh Administrator@ZETA "echo hi"


-- the command works, but on ZETA the Windows Event Log now says:

sshd: PID 7068: error: get_socket_address: getnameinfo 2 failed: Unknown error

Calling this often fills the Event Log with errors.

Starting sshd on command line in debug mode:

 /usr/sbin/sshd -ddd

-- produces no error. It also runs under different user and I had to chown administrator /var/empty for it to work.

Trying to start sshd in debug mode as Windows service, as recommended in https://cygwin.com/ml/cygwin/2014-03/msg00488.html fails:

$ /usr/bin/cygrunsrv -I sshd -d "CYGWIN sshd_debug" -p /usr/sbin/sshd -a "-D -d -d -d" -y tcpip

/usr/bin/cygrunsrv: Error installing a service: OpenService: Win32 error 1073: The specified service already exists.

  • What is the openssh version? Run ssh -V to display the version number.
    – rda
    May 17 '16 at 21:14
  • @rda OpenSSH_6.9p1, OpenSSL 1.0.2d 9 Jul 2015
    – Muposat
    May 17 '16 at 21:45

To resolve your cygrunsrv error while installing an sshd_debug service, you also have to change the <service_name> and not only the <service display name> in:

cygrunsrv -I <service_name> -d "<service display name>" -p <service_path>


  • <service_name> is the windows internal service name
  • <service display name> is the name displayed in services.msc list

OR you have to stop and remove the already defined service sshd first, before trying to define it again using debug parameters.

Note: The commands below have to be entered in a shell with admin privileges. When sshd is run in debug mode with -d, -dd or -ddd, the server will not fork and will only process one connection and then stop.

To define a second sshd_debug service:

To install a second service named sshd_debug:

/usr/bin/cygrunsrv -I sshd_debug -d "CYGWIN sshd_debug" -p /usr/sbin/sshd -a "-D -d -d -d" -y tcpip

Note that a particular <service_name> or <service display name> cannot be defined more than once, otherwise an error will thrown by cygrunsrv.

Before you start your new sshd_debug service, the normal sshd service has to be stopped:

/usr/bin/cygrunsrv -E sshd

Now start the sshd_debug service:

/usr/bin/cygrunsrv -S sshd_debug

To redefine with the existing sshd service_name:

Another example which will make the cygrunsrv command from your question work (using the service name: sshd):

# Stop the service
/usr/bin/cygrunsrv -E sshd

# Remove the service
/usr/bin/cygrunsrv -R sshd

# Install using the same service_name with debug options
/usr/bin/cygrunsrv -I sshd -d "CYGWIN sshd_debug" -p /usr/sbin/sshd -a "-D -d -d -d" -y tcpip

# Start the service
/usr/bin/cygrunsrv -S sshd

To install a service under a specific account

/usr/bin/cygrunsrv -I sshd_debug -d "CYGWIN sshd_debug" -p /usr/sbin/sshd -a "-D -d -d -d" -y tcpip -u "<account_name>" -w "<password>"

Error: get_socket_address: getnameinfo 2 failed

The function get_socket_address throwing the error message is defined in canohost.c:

static char *
get_socket_address(int sock, int remote, int flags)
    switch (addr.ss_family) {
    case AF_INET:
    case AF_INET6:
        /* Get the address in ascii. */
        if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
            sizeof(ntop), NULL, 0, flags)) != 0) {
            error("get_socket_address: getnameinfo %d failed: %s",
                flags, ssh_gai_strerror(r));
            return NULL;
        return xstrdup(ntop);

It calls a function getnameinfo with flag NI_NUMERICHOST, which should return a string with the human readable IP address of either the (remote) peer_ipaddr or the local_ipaddr. However, the function fails with an unknown EAI_SYSTEM error (A system error occurred).

So this does not help a lot, but it might indicate that the error has to do with DNS name resolution.

To troubleshoot you could check if the name resolution is working:

# netstat: check where sshd listens and if you have any errors
netstat -ano | grep ":22"
netstat -ao | grep ":22"

# reverse dns lookup
nslookup <remote_ip_address>
nslookup <local_ip_address>

# forward dns lookup (using the hostnames returned by the above commands)
nslookup <remote_hostname>
nslookup <local_hostname>

# or for example using dig

# reverse dns lookup
dig -x <remote_ip_address>
dig -x <local_ip_address>

# forward dns lookup (using the hostnames returned by the above commands)
dig <remote_hostname> +search
dig <local_hostname> +search
  • The reverse dns lookup should return the fqdn
  • The forward dns lookup should return the IP address
  • Thank you. This does not work for me, however. Both second service and redefining existing service succeed, but cannot start:$ /usr/bin/cygrunsrv -S sshd_debug1 /usr/bin/cygrunsrv: Error starting a service: QueryServiceStatus: Win32 error 1062: The service has not been started. . Normal sshd service always starts.
    – Muposat
    May 17 '16 at 18:39
  • Also after "Install using the same service_name with debug options" I don't know how to restore what was installed before.
    – Muposat
    May 17 '16 at 18:43
  • On my system I had the same, it could be a bug or something else not working. I had to define the service twice using cygrunsrv -I (on the second attempt I had an error: service already exists...) but after that the start command cygrunsrv -S worked. Also check netstat -ano and the task manager (all processes) if the sshd process is still running, I had to kill it manually sometimes.
    – rda
    May 17 '16 at 18:44
  • To restore the original configuration, stop any running sshd service cygrunsrv -E <service>, remove the sshd services cygrunsrv -R sshd (and optional cygrunsrv -R sshd_debug). Then from a privileged shell run /usr/bin/ssh-host-config. You can also check what the script does exactly, by running cat /usr/bin/ssh-host-config | grep -B 2 -A 10 "cygrunsrv -I"
    – rda
    May 17 '16 at 18:56
  • Service restored by ssh-host-config. I will try to run debug as a separate service. So far no luck though.
    – Muposat
    May 17 '16 at 19:13

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