Using Putty and OpenSSH

[edencrow]

I've just installed Ubuntu Server 12.04.3 LTS and am trying to set-up OpenSSH so that I can use Putty on my Windows 7 machine located on the same network to access the Linux machine.
Using 'ssh localhost' on the Linux machine allows me to SSH into the same machine, however trying to access the Linux machine with Putty on the Windows 7 machine (using the IP address given under ifconfig's 'inet address') results in the error 'server unexpectedly closed network connection'.
OpenSSH is installed and the sshd_config file has been left with its default values as changing the values as suggested at https://help.ubuntu.com/community/SS...SH/Configuring gave the same result with Putty.

[Lars Noodén]

Are you using UFW or iptables to filter your server? If so, then you'll need to open up port 22 (ssh)

sudo ufw allow ssh

[edencrow]

Are you using UFW or iptables to filter your server? If so, then you'll need to open up port 22 (ssh)

sudo ufw allow ssh

I'm not sure if I'm using UFW or iptables, I've just got the default Ubuntu with LAMP installation, perhaps there is a way I can find out to tell you? Saying that, I entered the command you suggested and got the following:

Rules updated
Rules updated (v6)

This then changed my Putty error message to 'Network Error: Connection timed out', what would I need to do next?

[steeldriver]

Do you still have the modified sshd_config file on the target server? does it allow PasswordAuthentication (I noticed the instructions you linked say to disable that option) - you will need that option at least until you set up key-based authentication

[Lars Noodén]

I'm not quite sure how to reproduce this problem.

Lack of keys would give an error something like 'Permission denied (publickey,keyboard-interactive)', when you have password authentication turned off but try anyway.

[edencrow]

Do you still have the modified sshd_config file on the target server? does it allow PasswordAuthentication (I noticed the instructions you linked say to disable that option) - you will need that option at least until you set up key-based authentication

Here is my sshd_config file currently, which has gone back to the original server unexpectedly closed network connection:

Host *
# ForwardAgent no
# ForwardX11 no
# ForwardX11Trusted yes
# RhostsRSAAuthentication no
# RSAAuthentication yes
PasswordAuthentication yes
# HostbasedAuthentication no
# GSSAPAuthentication no
# GSSAPIDelegateCredentails no
# GSSAPIKeyExchange no
# GSSAPITrustDNS no
# BatchMode no
# CheckHostIP yes
# AddressFamily any
# ConnectTimeout 0
# StrictHostKeyChecking ask
# IdentifyFile ~/.ssh/identity
# IdentifyFile ~/.ssh/id_rsa
# Identifyfile ~/.ssh/id_dsa
Port 22
# Protocol 2,1
# Cipher 3des
# Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfiur128,aes128-cbc,3des,cbc
# MACs hmac-md5,umac-64@openssh.com,hmac-ripem160
# EscapeChar ~
# Tunnel no
# TunnelDevice any:any
# PermitLocalCommand no
# VirtualHostKey no
# ProxyCommand ssh -q -W %h%p gateway.example.com
SendEnv LANG LC_*
HasKnownHosts yes
GSAPIAuthentication yes
GSSAPIDelegateCredentials no

[steeldriver]

That looks like /etc/ssh_config (the ssh client config file) - not /etc/sshd_config (the server config file)

[Lars Noodén]

"GSAPIAuthentication yes" is not in the default and looks spelled wrong. Can you rem that out or temporarily use a default configuration file?

Port 22
Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
UsePrivilegeSeparation yes
KeyRegenerationInterval 3600
ServerKeyBits 768
SyslogFacility AUTH
LogLevel INFO
LoginGraceTime 120
PermitRootLogin yes
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
UsePAM yes

You can test the configuration file's syntax with the -T option:

/usr/sbin/sshd -T

[edencrow]

That looks like /etc/ssh_config (the ssh client config file) - not /etc/sshd_config (the server config file)

Ah, yes, it does indeed say 'This is the ssh client system-wide configuration file'. Many apologies, I am new at this. I've put the client configuration file back to its default values:

Host *
# ForwardAgent no
# ForwardX11 no
# ForwardX11Trusted yes
# RhostsRSAAuthentication no
# RSAAuthentication yes
# PasswordAuthentication yes
# HostbasedAuthentication no
# GSSAPAuthentication no
# GSSAPIDelegateCredentails no
# GSSAPIKeyExchange no
# GSSAPITrustDNS no
# BatchMode no
# CheckHostIP yes
# AddressFamily any
# ConnectTimeout 0
# StrictHostKeyChecking ask
# IdentifyFile ~/.ssh/identity
# IdentifyFile ~/.ssh/id_rsa
# Identifyfile ~/.ssh/id_dsa
# Port 22
# Protocol 2,1
# Cipher 3des
# Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfiur128,aes128-cbc,3des,cbc
# MACs hmac-md5,umac-64@openssh.com,hmac-ripem160
# EscapeChar ~
# Tunnel no
# TunnelDevice any:any
# PermitLocalCommand no
# VirtualHostKey no
# ProxyCommand ssh -q -W %h%p gateway.example.com
SendEnv LANG LC_*
HasKnownHosts yes
GSSAPIAuthentication yes
GSSAPIDelegateCredentials no

However, I can not seem to be able to find a file named 'sshd_config' within /etc/ssh or /etc/. Is there somewhere else on my system I should look or a default example that I can copy over?

EDIT: Lars, looks like we posted at the same time, am reading the response from you and The Cog atm.

[The Cog]

Turning on the firewall when you are already having connectivity issues isn't helpful. Let's turn it off again:

sudo ufw disable

Let's have a look at what ports are listening on the Ubuntu server. Please post the results of:

netstat -lnt

Please check that you are setting putty to use port 22 (should happen when you select ssh, but its default is for telnet on port 23). The symptoms you describe could be explained by putty trying to connect to telnet 23 instead of ssh 22.