OpenSSH sshd on Windows Subsystem for Linux

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Internal

Overview

This article contains the procedure to configure a Windows Subsystem for Linux sshd to start at boot and allow ssh access to the Windows host.

Procedure

Installation

OpenSSH server should be installed by default: /usr/sbin/sshd should exist.

If it is not, download and install the appropriate packages:

dpkg -i ./libssl1.0.2_1.0.2l-2_amd64.deb \
       ./openssh-client_7.4p1-10_amd64.deb \
       ./libprocps6_3.3.12-3_amd64.deb \
       ./libncurses5_6.0+20161126-1_amd64.deb \
       ./procps_3.3.12-3_amd64.deb \
       ./openssh-server_7.4p1-10_amd64.deb

UsePrivilegeSeparation

Turn UsePrivilegeSeparation off by setting:

UsePrivilegeSeparation no

in /etc/ssh/sshd_config.

This is required to prevent sshd startup error that manifests in logs as:

chroot("/var/run/sshd"): Function not implemented [preauth]

Regenerate Server Keys

Regenerate the server keys following the procedure described here:

Regenerate Server Keys

This is required to prevent sshd startup error that manifests in the logs as:

debug1: list_hostkey_types:
No supported key exchange algorithms

Configure User Access

Add allowed public keys in ~/.ssh/authorized_keys

Set acceptable permissions:

cd ~
chmod -R go-rwx .ssh

Start the sshd Server

bash
sudo su -
/etc/init.d/ssh start

Start the sshd Server at Boot

Passwordless Sudo

Give passwordless sudo privileges the user that is supposed to start the server, by editing the sudo configuration file with visudo. More details: Allow a user to run commands as root without a password.

Windows Startup Script

Create autostartssh.vbs with the following content:

set ws=wscript.createobject("wscript.shell")
ws.run "C:\Windows\System32\bash.exe -c 'sudo /etc/init.d/ssh start'",0

Automatically Execute the Windows Startup Script at Boot

Task Scheduler -> Create Basic Task -> ...

TODO: this did not work, revisit.

Configure the Windows Firewall

Add a Custom Windows Firewall Rule

Status

/etc/init.d/ssh status

Start/Stop

/etc/init.d/ssh start|stop