hpc documentation - abstract:mills:system_access:system_access

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====== Connecting to Mills=====

//This section uses the wiki's [[http://docs-dev.hpc.udel.edu/doku.php#documentation-conventions|documentation conventions]].//
===== 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>

===== Logging on to Mills =====
You need a [[abstract:mills:account:account|mills account]] to access the login node. For example,  using SSH to connect to the Mills login node with account ''traine'', type:

<code bash>
    ssh traine@mills.hpc.udel.edu
</code>

Please refer to Windows and Mac/Linux related sections for specific details: 
  * [[:abstract:mills:system_access:windows|Windows]]
  * [[:abstract:mills:system_access:linux|Mac/Linux]]


Once you are logged into Mills, your account is configured as a member of an investing-entity group name (workgroup) which determines access to your group's compute nodes, queues and storage resources on Mills. Setting your workgroup environment is required in order to submit jobs to the Mills 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>

You will need to know [[:training:linux:linux|Unix/Linux]] and [[:training:hpc:hpc|HPC]] concepts before using Mills. Use the <html><span style="color:#ffffff;background-color:#2fa4e7;padding:3px 7px !important;border-radius:4px;">sidebar</span></html> to navigate documentation about Mills, from accessing the cluster to running applications, using [[:software:software|software]] and available [[:training:training|training]].


===== 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.
See the **man** page for **screen** for details.

<note tip>
Suppose you have a significant amount of interactive work to be done on the cluster, but you have a 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>