Qtech user guide

This site uses Just the Docs, a documentation theme for Jekyll.

Search

Connecting to the workstation

SSH Shell

SSH shell is enabled on qtech. Linux and macOS already have an ssh client. On Windows, different clients are available. A very popular client is PuTTY.

To connect to qtech, use the following command:

ssh username@qtech.fisica.unimi.it

username is in general your surname (lowercase).

At the first login, you will need to insert the password provided during the creation of the account. You will be then asked to insert it again and then to insert a new, personal password. The general rules for strong passwords apply. Although all basic security measures are implemented to protect the workstation, it is in general unsafe to use the same credentials of other email/internet/bank accounts.

Contact the administrator if you need a password reset

To simplify the authentication process, a key authentication system is recommended

Authentication through SSH keys

Linux / macOS

A public/private key pair is required. If you don’t have one already, execute the following commands on your personal computer

mkdir ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa

From Linux, you can simply issue the command

ssh-copy-id username@qtech.fisica.unimi.it

to copy the public key to qtech. Your password will be asked, for the last time.

On macOS, the command ssh-copy-id can be installed with Macports or Homebrew. Otherwise, the public key can be copied manually with the command

cat ~/.ssh/id_rsa.pub | ssh username@qtech.fisica.unimi.it "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys"

Windows

This guide shows how to use PuTTY to generate a key pair and to copy the public key to the workstation.

For further information: https://help.ubuntu.com/community/SSH/OpenSSH/Keys

REMARK Commands issued from the SSH terminal are interrupted in case of a logout or disconnection. Long tasks may thus get killed if for any reason the client disconnects. To avoid this, please make use of the screen command as reported below

Use of the screen command

The screen command creates a terminal that is not interrupted in case of disconnection. It is later on possible to reattach to that terminal and continue the work. The basic usage is

ssh username@qtech.fisica.unimi.it
screen
comando-lungo

You can detach from the terminal with the key combination CTRL + A, D.

To reconnect to an open screen session, use the command

screen -r

To list the open session, use the command

screen -ls

With the command exit you logout from the virtual terminal.

For further information on the screen command, use man screen or use Google!

Mounting your home directory on your local computer with sshfs

It is possible to mount your home directory on qtech on your personal computer using sshfs. After having installed the sshfs command on your local computer, you can issue the command

sshfs username@qtech.fisica.unimi.it /path/on/your/pc

sshfs can be easily installed on Linux using your distribution package manager. On macOS, you can install [Fuse and the sshfs package][4].

There are different SSHFS applications for Windows, but I haven’t tried any of those yet.

Graphical interface

There are two ways to use applications with a graphical interface: X11 forwarding or remote desktop.

X11 forwarding

You can view graphical applications on your desktop by forwarding the X11 graphical system through ssh. In order to do so, a X11 server must be installed on your local computer:

  • Linux: X11 is already available
  • OSX: download available here
  • Windows: You need to install cygwin or Xming (not tested)

To forward X11 use the command

ssh -Y username@qtech.fisica.unimi.it

** WARNING ** As for text commands, graphical applications are terminated in case of discconnection. To avoid this kind of problem, use Remote desktop as follows.

Remote desktop

Qtech uses TurboVNC as a VNC server. Each user can start a remote desktop using any VNC client. The configuration has been tested on Ubuntu and macOS with the default remote desktop applications.

  1. Connect to ssh and launch the VNC server with the commmand

     vncserver -geometry 1280x800 -depth 24 -localhost

    the option -geometry is followed by the required resolution.

    The first time the server will require you to set a password for the remote desktop. It is possible to leave the password empty, as the connection is already encrypted through SSH.

    The server program will report that it started correctly on display number :[n], with a message like

     Desktop 'TurboVNC: qtech:1 (qtech)' started on display qtech:1

    Please take note of the number following qtech:.

  2. For safety reasons, the connection is allowed only through an SSH tunnel. On the client computer, issue the command

     ssh -f -N -L 5900:localhost:5901 username@qtech.fisica.unimi.it

    where the number 5901 must be replaced with the number 5900 + n, where n is the number of display reported by the server (see step 1).

  3. Now, use your VNC client to connect to localhost:5900. Some clients use the syntax localhost:0. It is possible to connect and reconnect to the server as long as it is running. To stop the server (and all the programs that are being executed) use the command (on qtech)

     vncserver -kill :1

    where :1 must be replaced with the screen number obtained at Step 1.