Access to the system


The access to Calendula by users is done through the SSH Secure Shell protocol. This protocol is used to access remote machines through a network. It allows the remote work through a command interpreter, although it also allows to redirect the traffic of the graphic programs of the remote computer towards the screen of the local computer.

SSH uses encryption techniques that prevent third parties from accessing communications content. As it is a secure protocol, concepts such as public/private key, fingerprint, etc. come into play. It is not the purpose of this manual to go into detail on these concepts but a brief description is necessary to fully understand the connection process and thus ensure the confidentiality of the traffic between the user's system and the SCAYLE system.

The concept of a unique fingerprint or public key is an alphanumeric string of characters that identifies a specific server and serves to ensure that the server that is answering is really the one we wanted to connect to.

The URL calendula.scayle.es is the access to the supercomputer, but behind this address there are really two different servers (called frontend1 and frontend2) that are in charge of dealing with the logon requests of remote users. In this way, the number of users who simultaneously access Calendula is distributed between the two servers. But this solution, raises the disadvantage that the two servers have different public keys, although from the outside respond to the same address. This raises the problem of public keys ssh since the first time the key of one of the frontend is saved and the following times when changing the frontend where you log in may appear a security alert warning of a possible attack 'man-in-the-middle'.

In the file are the keys of the two frontends. You can copy the contents of this file to your user's $HOME/.ssh/know_hosts file on your local machine. The fingerprints of the two frontends are:

Codificación RSA frontend1: 2c:e4:79:a9:91:13:c2:30:62:29:79:b0:d2:11:f3:7d
Codificación SHA1 frontend1: 1muBCHElWojD1qBchZ1qAkRjFEekflaZGQBx6gvoRyk
Codificación RSA frontend2: ec:56:8c:52:77:86:4c:a5:61:57:72:2d:f9:68:20:ad
Codificación SHA1 frontend2: yV4p5DZ8oy86fRYd6LAAiFjf3bIXgbMaKnPrwxt8+/s

Windows operating systems do not install by default any utility that allows remote access to other systems using the SSH protocol.
From SCAYLE we recommend the following programs to make the connection to our systems:

  • PuTTY. It is a free, lightweight utility that is very easy to install on any of the latest versions of Windows.
  • MobaXterm. This tool is much more powerful than the previous one and includes multiple tools such as SFTP browser, X11 server, etc.
  • Windows Subsystem for Linux. Compatibility layer created by Microsoft to run Linux natively on Windows. There are different distributions Linux that can be installed (Ubuntu, OpenSUSE, Debian,...).

Once one of the above programs has been installed, the configuration values for access to Calendula are as follows:

Host Name (or IP address): calendula.scayle.es
Port: 2222
Connection type: SSH

Access to the system from Linux or macOS operating systems is much easier since these operating systems (at least the vast majority of distributions) are configured by default with the SSH protocol client program.
To connect from these systems to Calendula, it is only necessary to enter the following command in a terminal:

ssh -X  -p 2222

You will ask us for our user's password and we will log in.
As with the Windows tools connection, ssh access checks that the public key of the system we are connecting to matches the one stored in it. As indicated above, to avoid the security warning, you must copy the keys of the frontends of the system to the file.

$HOME/.ssh/know_hosts

Once you have connected to our system, you enter one of the two login nodes from which you can transfer data, edit your job submission scripts, work with the file system, etc.

IMPORTANT: No calculation activity is allowed in these nodes. Note that these are servers shared between all users and activities that require a large amount of memory or CPU time, will harm the work of other users. Therefore, there are limits set on CPU time and the number of processes a user can open.