For most ATLAS work, you will usually want to connect to a remote computer rather than working directly on your own laptop. This is because remote servers usually have more resources available an have ATLAS software already installed.
We will work on the CERN lxplus server unless your instructor informs you otherwise. To log into lxplus from terminal, use:
ssh -Y -C <cern-username>@lxplus.cern.ch
From a Linux laptop you should instead use
-X(upper case X) instead of
-Yin the ssh command.
In order to keep all of your tutorial work in a single place,
create a dedicated directory. You can name it however you want,
but we will assume it is called
To connect to a remote server using terminal, use the
command. The basic syntax is:
ssh [optional arguments] <username>@<server-address>
You will be prompted for your password and after successfully entering it, you will be logged into the remote computer. By default, you will begin in your home directory.
Any configurations from your computer will not be available on the remote computer, so you will need to set them up by hand.
If you have a slow connection to the remote computer (often due to physical distance or network traffic), use the argument
-Cto speed up the connection. This causes all information passed back and forth to be compressed. This option can slow down an already fast connection due to the compression step taking time.
X11 is a system that allows windows to be opened locally from a remote computer that you are connected to. This is particularly useful for opening any king of graphics, such as when drawing ROOT histograms.
You may need to install an X11 server on your personal computer.
To test whether you already have one installed, use the
command on your local computer. If a new terminal-like window
opens, X11 is installed. Alternatively you can usually use the
xeyes command to open an interactive set of eyes.
If you do not have X11 installed, you should install it now. There are multiple X11 server options depending on your OS:
If you want to make use of the X11 functionality when connecting
to a remote computer, use the
-Y option (
-X if you are using
a Linux laptop). You can check that X11 forwarding is active with
xterm command on the remote computer.
xeyesis currently unavailable on lxplus and may not be available on whichever other remote machine you are using.
It is possible to store ssh configurations in a file to simplify
connection commands. To do this, create/edit
example block is:
Be sure to replace
<username>with your username on the host computer.
With this configuration, you can connect to lxplus with the command:
This is equivalent to:
ssh -Y -C <username>@lxplus.cern.ch
Whether you are logging into lxplus or another machine, it is possible to connect without needing to input your password every time using passwordless ssh.
For details about connecting to a remote server using VS Code, please see the VS Code guide.