hpc documentation - abstract:caviness:system_access:system_access

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====== Connecting to Caviness =====


===== Secure shell program (SSH) =====

Use a secure shell program/client (SSH) to connect to the cluster and a secure file transfer
program to move files to and from the cluster.

There are many suitable secure clients for Windows, Mac OS X, and UNIX/Linux. We recommend PuTTY and Xming for Windows users. Macintosh and UNIX/Linux users can use their pre-installed SSH and X11 software. (Newer versions of Mac OS X may not have a current version of X11 installed. See the Apple web site for
[[http://support.apple.com/kb/HT5293|X11 installation instructions]].)

<note tip>IT strongly recommends that you configure your clients as described in the online X-windows (X11) and SSH documents
([[http://udeploy.udel.edu/software/putty-with-xming|Windows]] /
[[http://www.udel.edu/it/research/training/config_laptop/linuxAgent.html|Linux/MacOSX]]). </note>

<note important>
Your HPC home directory has a ''.ssh'' directory. Do not manually erase or
modify the files that were initially created by the system. They facilitate communication between
the login (head) node and the compute nodes. Only use standard **ssh** commands to add keys to the
files in the ''.ssh'' directory.
</note>

Please refer to Windows and Mac/Linux related sections for specific details using the command line on your local computer:
  * [[:abstract:caviness:system_access:windows|Windows]]
  * [[:abstract:caviness:system_access:linux|Mac/Linux]]

===== Logging on to Caviness =====
You need a [[abstract:caviness:account:account|Caviness account]] to access the login node and it is very important to review the information about [[abstract:caviness:account:account#cluster-accounts|cluster accounts]] and [[abstract:caviness:account:account#cluster-groups|cluster groups]] before connecting. For example, using SSH to connect to the Caviness login node with account ''traine'', type:

<code bash>
    ssh traine@caviness.hpc.udel.edu
</code>
or if you need you use X-Windows requiring X11 forwarding, then use
<code bash>
    ssh -Y traine@caviness.hpc.udel.edu
</code>

You may set up direct SSH key authentication on Caviness once you are on the system by adding the desired public key to your authorized_keys file in the .ssh directory inside your home directory. Once you have a SSH key set up this way, you can access Caviness directly by running ''ssh caviness.hpc.udel.edu'' or ''ssh -Y caviness.hpc.udel.edu''.

Once you are logged into Caviness, your account is configured as a member of an investing-entity group name ([[abstract:caviness:app_dev:compute_env#using-workgroup-and-directories|workgroup]]) which determines access to your group's compute nodes, queues and storage resources on Caviness. Setting your workgroup environment is required in order to submit jobs to the Caviness cluster. For example, the ''traine'' account is a member of the ''it_css'' workgroup. To start a shell in the ''it_css'' workgroup, type:

<code bash>
    workgroup -g it_css
</code>

Please review all the information regarding your computing environment especially the [[abstract:caviness:app_dev:compute_env#startup-and-logout-scripts|startup and logout scripts]] and [[abstract:caviness:app_dev:compute_env#using-valet-and-your-unix-environment|using VALET]]. You will need to know [[:training:linux:linux|Unix/Linux]] and [[:training:hpc:hpc|HPC]] concepts before using Caviness. Use the <html><span style="color:#ffffff;background-color:#2fa4e7;padding:3px 7px !important;border-radius:4px;">sidebar</span></html> to navigate documentation about Caviness, from accessing the cluster to running applications, using [[:software:software|software]] and available [[:training:training|training]].

To learn about launching GUI applications on Caviness from a Windows machine, refer to [[abstract:caviness:runjobs:schedule_jobs#launching-gui-applications-x11-forwarding|Schedule Jobs]] page.

<note important>Please review the [[technical:generic:caviness-login-cpu-limit|document]] summarizing the current resource limits and the need for and implementation of additional limits on the Caviness cluster login nodes.</note>
===== Screen sessions =====

When an SSH session is ended intentionally or by a loss of connectivity, you cannot generally restart it and resume your work. The UNIX **screen** command provides a useful solution. This
command creates a virtual terminal window session that continues to run after you are logged off. It allows you to reattach the same virtual terminal window session and resume working.

<note tip>
Suppose you have a significant amount of interactive work to be done on the cluster, but you have an interruption coming up shortly, such as lunch.
You can start a screen session and work until lunchtime.  Log out and when you come back from lunch, reattach the screen session and continue your work. Even output from jobs will be displayed, as if you never left.
</note>

<note important>
If you are using an unstable network connection, for example, a laptop that drops your connection when it sleeps, you may want to start a screen session before you lose connectivity.
</note>

See the **man** page for **screen** for details or review a short video [[https://www.youtube.com/watch?v=_ZJiEX4rmN4|How to Use the Screen Command on Linux]] to get started.