I am trying to log in to my server with ssh keys (I use putty to do it) but every time I try to connect it says Network error: Connection refused. I believe it's something wrong with the public key not sure though. The key looks like this:

rsa-key-public AAAAB3NzaC1yc2EAAAABJQAAAQEAx+KoPhVxfBrnN8cFb+hG9MveY0cfNpn9mAcN

but all in one line. I used puttygen to create the key and it looked like this by deafult:

Comment: "rsa-key-public"

Output of cat /etc/ssh/sshd_config:

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
#Port 2222
# Use these options to restrict which interfaces/protocols sshd will bind to 
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key 
KeyRegenerationinterval 3600
ServerKeyBits 2048

# Logging
SyslogFacility AUTH 
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin prohibit-password 
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile ~/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts 
RhostsRSAAuthentication no
# similar for protocol version 2 
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication 
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED) 
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with 
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords 
PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no 
#KerberosGetAFSToken no 
#KerberosOrLocalPasswd yes 
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

Xl1Forwarding yes 
Xl1DisplayOffset 10 
PrintMotd no
PrintLastLog yes 
TCPKeepAlive yes 
#UseLogin no

#MaxStartups 10:30:60 
*Banner /etc/issue.net

# Allow client to pass locale environment variables 
AcceptEnv LANG LC *

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing, 
# and session processing. If this is enabled, PAM authentication will 
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass 
# the setting of *PermitRootLogin without-password*.
# If you just want the PAM account and session checks to run without 
# PAM authentication, then enable this but set PasswordAuthentication 
# and ChallengeResponseAuthentication to 'no'.
UsePAM no

Output service ssh status / systemctl status ssh.service:

peter@PM-server:-$ service ssh status
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/systemissh.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2017-04-03 16:02:13 CEST; 3h 37min ago
 Main PID: 1577 (sshd)
    Tasks: 7 (limit: 4915)
   Memory: 23.1M
      CPU: 3.774s
   CGroup: /system.slice/ssh.service 
           ├─1577 /usr/sbin/sshd -D 
           ├─2351 sshd: peter [priv] 
           ├─2359 sshd: peter@pts/0 
           ├─2360 -bash
           ├─2395 systemctl status ssh.service
           └─2400 pager

Apr 03 16:25:11 PM-server sudo[2030] :pam_unix(sudo:session): session opened for user root by peter(uid=0)
Apr 03 16:32:45 PM-server sudo[2030] :pam_unix(sudo:session): session closed for user root
Apr 03 16:50:45 PM-server sshd[2068] : Accepted password for peter from port 57813 ssh2
Apr 03 17:19:14 PM-server sudo[2135]     peter : TTY=pts/0 ;  PWD/home ; USER=root ; COMMAND/bin/chown peter:peter peter
Apr 03 17:19:14 PM-server sudo[2135] :pam_unix(sudo:session): session opened for user root by peter(uid=0)
Apr 03 17:19:14 PM-server sudo[2135] :pam_unix(sudo:session): session closed for user root
Apr 03 19:25:09 PM-server sshd[2351] : Accepted password for peter from port 56635 ssh2
Apr 03 19:26:05 PM-server sudo[2372]     peter : TTY=pts/0 ; PWD/home/peter ; USER=root ; COMMAND/bin/systemctl
Apr 03 19:26:05 PM-server sudo[2372] :pam_unix(sudo:session): session opened for user root by peter(uid=0)
Apr 03 19:28:14 PM-server sudo[2372] :pam unix(sudo:session): session closed for user root

Here is the out put of sudo systemctl.

Output of sudo sshd -T

    port 22
    protocol 2
    addressfamily any
    listenaddress [::]:22
    usepam yes
    serverkeybits 1024
    logingracetime 120
    keyregenerationinterval 3600
    x11displayoffset 10
    maxauthtries 6
    maxsessions 10
    clientaliveinterval 0
    clientalivecountmax 3
    streamlocalbindmask 0177
    permitrootlogin without-password
    ignorerhosts yes
    ignoreuserknownhosts no
    rhostsrsaauthentication no
    hostbasedauthentication no
    hostbasedusesnamefrompacketonly no
    rsaauthentication yes
    pubkeyauthentication yes
    kerberosauthentication no
    kerberosorlocalpasswd yes
    kerberosticketcleanup yes
    gssapiauthentication no
    gssapikeyexchange no
    gssapicleanupcredentials yes
    gssapistrictacceptorcheck yes
    gssapistorecredentialsonrekey no
    passwordauthentication yes
    kbdinteractiveauthentication no
    challengeresponseauthentication no
    printmotd no
    printlastlog yes
    x11forwarding yes
    x11uselocalhost yes
    permittty yes
    permituserrc yes
    strictmodes yes
    tcpkeepalive yes
    permitemptypasswords no
    permituserenvironment no
    uselogin no
    compression delayed
    gatewayports no
    usedns no
    allowtcpforwarding yes
    allowagentforwarding yes
    allowstreamlocalforwarding yes
    streamlocalbindunlink no
    useprivilegeseparation yes
    fingerprinthash SHA256
    pidfile /var/run/sshd.pid
    xauthlocation /usr/bin/xauth
    ciphers chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-                 ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
    macs umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-        etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-        64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
    versionaddendum none
    kexalgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-                                nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-        group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-        sha256,diffie-hellman-group14-sha1
    hostbasedacceptedkeytypes ecdsa-sha2-nistp256-cert-        v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-        cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-        v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-        ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
    hostkeyalgorithms ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-        nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-        ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ecdsa-sha2-        nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-        sha2-256,ssh-rsa
    pubkeyacceptedkeytypes ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-        sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-        ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ecdsa-sha2-        nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-        sha2-256,ssh-rsa
    loglevel INFO
    syslogfacility AUTH
    authorizedkeysfile .ssh/authorized_keys .ssh/authorized_keys2
    hostkey /etc/ssh/ssh_host_rsa_key
    hostkey /etc/ssh/ssh_host_ecdsa_key
    hostkey /etc/ssh/ssh_host_ed25519_key
    acceptenv LANG
    acceptenv LC_*
    authenticationmethods any
    subsystem sftp /usr/lib/openssh/sftp-server
    maxstartups 10:30:100
    permittunnel no
    ipqos lowdelay throughput
    rekeylimit 0 0
    permitopen any
  • Ok, you are have customized your /etc/ssh/sshd_config and at the moment it is running but not listen to any port: #Port 2222. Also it listen only to IP address At first look, this could be the reason why our test (ssh $USER@localhost which means ssh current-user-name@ -p 22) doesn't pass. So just for the test change these two lines like this: Port 22 and #ListenAddress - it will listen to any IP to port 22. Restart the service: sudo systemctl restart ssh.service (or sudo service ssh restart), and try to connect again: ssh $USER@localhost. – pa4080 Apr 3 '17 at 18:48
  • Also this line is incorrect: AuthorizedKeysFile ~/.ssh/authorized_keys. It must be: AuthorizedKeysFile %h/.ssh/authorized_keys. Here you are, how /etc/ssh/sshd_config looks by default in Ubuntu Server 16.04.1. – pa4080 Apr 3 '17 at 19:11
  • Ok, I will make these changes later today and report back how the test went. – KV-2 Apr 4 '17 at 7:14
  • I have now done the changes in the sshd_config file, restarted the ssh service and executed ssh peter@PM-server. I got this output ssh: connect to host pm-server port 22: Connection refused. – KV-2 Apr 4 '17 at 14:34
  • I think there is something wrong in /etc/ssh/sshd_config. Please try to use the original configuration that I shared - just copy and paste all lines in your sshd_config file. Then use this command: sudo sshd -T to do a quick test of the syntax of the configuration file. – pa4080 Apr 4 '17 at 14:56

Here you go short manual covering the whole process:

How to SSH Ubuntu from Windows via PuTTY, using keys

I. Generate SSH 'key pair' in Ubuntu and create authorized_keys file

$ ssh-keygen -t rsa -b 4096 Enter
Generating public/private rsa key pair.
Enter file in which to save the key (/home/$USER/.ssh/id_rsa): Enter
Created directory '/home/$USER/.ssh'.
Enter passphrase (empty for no passphrase): type your passphrase Enter
Enter same passphrase again: retype your passphrase Enter

$ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys Enter 
$ chmod go-w ~/ Enter
$ chmod 700 ~/.ssh Enter
$ chmod 600 ~/.ssh/authorized_keys Enter

$ ls -la ~/.ssh Enter
drwx------ 2 user user 4096 апр  2 17:21 .
drwxr-xr-x 3 user user 4096 апр  2 17:40 ..
-rw------- 1 user user  738 апр  2 17:21 authorized_keys
-rw------- 1 user user 3243 апр  2 17:15 id_rsa
-rw-r--r-- 1 user user  738 апр  2 17:15 id_rsa.pub

Please note we don't need to use sudo. If authorized_keys already exists the output redirection >> just will append a new entry.

Make a test - SSH to localhost using the username of the current user:

$ chmod 600 ~/.ssh/id_rsa.pub
$ ssh $USER@localhost -i ~/.ssh/id_rsa -p 22 -v

Where: (1) you can omit the options -i ~/.ssh/id_rsa -p 22, because these are the default values, and (2) -v will turn on verbose mode. Further information can be found in man ssh.

Please note, this test will pass "only" with the default configuration of /etc/ssh/sshd_config. Here is the default sshd_config of Ubuntu 16.04.

II. Convert id_rsa private key into .ppk format and use it

Where .ppk means PuTTY Private Key.

Approach 1: Using puttygen for Linux:

The idea for this additional editing came from this topic where was discussed the conversion from .ppk into an OpenSSH compatible format.

  1. Install putty-tools in Ubuntu. Open a terminal and type:

    sudo apt install putty-tools
  2. Convert the private key:

    puttygen ~/.ssh/id_rsa -O private -o ~/.ssh/converted_id_rsa.ppk
  3. Copy the converted private key (converted_id_rsa.ppk) into Windows.

  4. Use this .ppk key with PuTTY to connect to Ubuntu. Screenshot.

Approach 2: Using puttygen for Windows

  1. Copy the private key (id_rsa) into Windows.

  2. Run 'PuTTY Key Generator' (puttygen.exe) and click on Load button. Screenshot.

  3. Switch to All Files (*.*) and Open your generated in Ubuntu (id_rsa) private key file. Screenshot.

  4. Enter the passphrase if there is one, then click on OK. An notification will be appeared - click on OK once again. Screenshot.

  5. Edit Key comment and Key passphrase if you need it and click on Save private key. Screenshot.

  6. Save your new .ppk key in a convenient location. Screenshot.

  7. Use this .ppk key with PuTTY to connect to Ubuntu. Screenshot.


  • I tried what you suggested and now it says "server refused our key" when I try to log in with it. Any ideas how to fix that? – KV-2 Apr 2 '17 at 13:40
  • I chmoded 700 .ssh and now it says "Network error: Connection refused" again. – KV-2 Apr 2 '17 at 13:51
  • @KV-2 I will edit my answer. – pa4080 Apr 2 '17 at 13:54
  • @KV-2 I've updated my answer. – pa4080 Apr 2 '17 at 15:06
  • thanks for the update, I will try it out when I get the time today. – KV-2 Apr 3 '17 at 6:25

Usually, Network error: Connection refused means that the server refused your SSH connection entirely. It didn't have a problem with the key PuTTY used with it because it didn't get that far in the connection process to even bother with keys. Instead, it refused the connection immediately. This is usually due to the server not running an SSH server (or the SSH server being broken), you having the wrong port, or you having the wrong server address.

However, you say that you only receive that error message when connecting using a public key while connecting using a password works fine. To add a public key for incoming connections, add the following line to ~/.ssh/authorized_keys on the server (create the file if it doesn't exist):

ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAQEAx+KoPhVxfBrnN8cFb+hG9MveY0cfNpn9mAcNhsfkEvxeG2EqLRYtaXUBXPgl3uILvXYbqG7HSBq/kZe/AICn/aK89rCGAozEepdeaYmy9EtmfPU8pFgTrgMils8X6b5kPPxCBZ2pfeL/q4SUke+/xpV1x98py6PHM8VmJaBciqvaa89QLvWf3IUuxm7798WvGUPlSMtuE2wnYsyJ4W65nBCs4PCROpaPmcmqiP0VF+Vm5vC3W/F00PC1w3R3BMdDoS2VJj7jQTR1Ralbn9cM185/pZY8lvkX4lEQMJvvwRM1Oy/g+J7+RbPR/XTrrRmKQq5mnWU0ICV5qvTnsc+Lyw==

Note that this:

  1. Starts with ssh-rsa
  2. Has no line breaks in the middle of it (remove them if present)
  3. Should be the public key (should start with AAAAB3) you're currently using (replace it with the new one if you've generated a new one)
  • It only says network error when I try to log in with the key. If I use log in with the password it works without any problem and when I issue the command sudo service ssh status it says it is active and running. I haven't changed port ethier, it's the standard port 22. I don't really know what to do. – KV-2 Apr 2 '17 at 14:38
  • OK, I've added how to add the public key to ~/.ssh/authorized_keys, which is the default way to add a public key for use with inbound SSH connections. Note that this won't work if the user's home directory is encrypted. – Chai T. Rex Apr 2 '17 at 14:47
  • +1 For this detailed explanation. OP is fighting with SSH couple of days, so I made something like a step-by-step manual. – pa4080 Apr 2 '17 at 16:05

This is a bit different format of the keys. Proper way to convert one to the other is to use ssh-keygen:

 ssh-keygen -i -f /path/to/public.key

The result for your key looks like this:

ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAQEAx+KoPhVxfBrnN8cFb+hG9MveY0cfNpn9mAcNhsfkEvxeG2EqLRYtaXUBXPgl3uILvXYbqG7HSBq/kZe/AICn/aK89rCGAozEepdeaYmy9EtmfPU8pFgTrgMils8X6b5kPPxCBZ2pfeL/q4SUke+/xpV1x98py6PHM8VmJaBciqvaa89QLvWf3IUuxm7798WvGUPlSMtuE2wnYsyJ4W65nBCs4PCROpaPmcmqiP0VF+Vm5vC3W/F00PC1w3R3BMdDoS2VJj7jQTR1Ralbn9cM185/pZY8lvkX4lEQMJvvwRM1Oy/g+J7+RbPR/XTrrRmKQq5mnWU0ICV5qvTnsc+Lyw==

Therefore on the single line with key identifier ssh-rsa, instead of the one you used. Also the newlines matter (there can be none).


Install the openssh-server package from Ubuntu Software Center. Or run command below in console if you’re on Ubuntu Server without GUI:

sudo apt-get install openssh-server

Once installed, the SSH service should be started automatically. If necessary, you can start (or stop, restart) the service manually via command:

sudo service ssh start

Port number 22 is default. To change the port, root login permission, you may edit the /etc/ssh/sshd_config file via:

sudo nano /etc/ssh/sshd_config

Remove the "#" from the sshd_config file, which is prefixed to Port 22

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