Installing cygwin sshd on a normal machine is pretty straightforward. You simply run ssh-host-config and walk through the prompts. On a Windows domain it’s more complicated. Your sshd will still run and you can still connect and run normal commands, but as far as I can tell there’s no way to elevate your permissions and do admin actions (that would trigger a UAC prompt if you were using the Windows GUI). To fix this we’ll need to run sshd as a domain user that has the permissions to setuid like it would on a unix. For some details check this post by Cygwin project lead Corinna Vinschen.

Make a domain account to run the service

I won’t cover creating a domain user, as that’s pretty simple and steps for that can be easily conjured with a web search. We’re going to call our domain user cyg_server, but you can call it whatever you want. That user is going to need the permissions to basically setuid (or whatever the Windows equivalent is called). Create a group policy object and link it to your org unit with the following policies:

Under Computer Configuration / Policies / Windows Settings / Security / Local Policies / User Rights Assignment add your user to the following policy settings

  • Act as part of the operating system
  • Create a token object
  • Deny log on locally
  • Deny log on through Remote Desktop
  • Replace a process level token

Once the policy is distributed you can install sshd or replace your existing local sshd.

Remove the existing sshd service and user

If you have an existing machine-local sshd running, get rid of it (you can use the Windows service tools (sc) as well).

cygrunsrv --stop sshd
cygrunsrv --remove sshd

Then delete the local cyg_server user. It’ll only serve to confuse you otherwise.

Update cygwin’s view of the domain users

From a cygwin terminal with admin rights, run these to update cygwin’s list of available domain users and groups. The ssh-host-config script will use these to decide if your chosen domain cyg_server user has the proper permissions to run the ssh daemon.

# these will obviously clobber your files, so if you want to preserve
# some users/groups you've made outside Windows you'll need to take steps
# to protect those changes

mkpasswd -l -d > /etc/passwd
mkgroup -l -d > /etc/group

You should be able to see your user in the list of users output by mkpasswd

$ mkpasswd -l -d | grep cyg_server # or your chosen username

You can see there that cygwin has mapped a cygwin user cyg_server to the domain user DMZ\cyg_server. In cygwin, we’ll use just cyg_server to refer to that user. (This is why it’s important to delete the existing cyg_server user if you already had a local sshd set up).

Run ssh-host-config

sshd has a handy setup script that will walk you through the process. The important options we want are:

  • strict modes -> yes
  • privilege separation -> yes
  • value of CYGWIN for the daemon - ntsec
  • user to run as -> cyg_server (or whichever one maps to your domain user in /etc/passwd)

Test it out

If you’ve done everything right, you should be able to connect over ssh with your domain credentials. Connect with the cygwin user name that maps to your domain account, e.g. wes, for LAN\wes. Once connected try to sc stop and sc start a service. It should work, rather than getting a permission failure message, like you would have before.