Install OpenSSH services

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Note

26 May 2020: systemctl file command revised.

27 May 2019: Security settings added.

11 Apr 2018: Page added.

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Intro

OpenSSH enables remote client computers and smartphones to access the server computer's text based terminal shell in a secured manner. "SSH" stands for secured shell.

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Install OpenSSH server

Execute:

$ sudo apt install openssh-server

The software will be installed at /etc/ssh.

In case of complaint of no directory, execute  to make directory first:

$ sudo mkdir /etc/ssh

Edit config file:

$ cd /etc/ssh
$ sudo gedit sshd_config

Specify:

# Port 22                             (which is the default port)
Port 2nnn                             (change to some other 4-digit port, 2nnn)
# PermitRootLogin prohibit-password   (meaning no password required)
PermitRootLogin no                    (meaning no root login)

(security settings added, 27 May 2019)

Restart the service:

$ sudo systemctl restart sshd.service
or
$ sudo systemctl restart ssh.service

Check status:

$ sudo systemctl status sshd.service

If found disabled:

$ sudo systemctl enable ssh

(status check added, 26 May 2020)

Change the internet router to permit the use of port 2nnn.

The above is already sufficient for use. Read https://help.ubuntu.com/lts/serverguide/openssh-server.html for more configurations, if desired.

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Install SSH client on Windows

Download Putty from https://www.putty.org/ and install.

Enter the Host Name, change the Port to 2nnn, highlight Default Settings and press Save:

"Only on clean exit" is the default. When the server's terminal window is exited with "exit" or "logoff", the PuTTY screen and connection would only close if other processes using the PuTTY connection have all been closed.

Press Open.

Accept the next screen to confirm the server's security key shown, if trusted. This would be necessary for the first time only.

Log in as the usual command terminal. No graphical interface is provided.

Use PuTTYgen that comes installed with PuTTY to generate key pairs, only if required. Read its Help.

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Configure for VNC

If PuTTY is used for VNC connection, config the tunnel by entering the Source port and Destination as follows, then press Add to move the setting to the upper window:

With "Local" selected, the Source port means the port of the client computer. It can be "5900" or any free port. "Localhost:5900" at the Destination means the host computer, not the client computer. "5900" refers to the port number on the host computer providing VNC server service.

Go back to the first screen, highlight Default Settings and press Save again.

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