hpc documentation - abstract:darwin:system_access:system_access

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====== Connecting to DARWIN =====


===== 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
([[https://www1.udel.edu/it/research/training/config_laptop/puTTY.shtml|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:darwin:system_access:windows|Windows]]
  * [[:abstract:darwin:system_access:linux|Mac/Linux]]

===== Logging on to DARWIN =====
You need a [[abstract:darwin:account:account|DARWIN account]] to access the login node and it is very important to review the information about [[abstract:darwin:account:account#cluster-accounts|cluster accounts]] and [[abstract:darwin:account:account#cluster-groups|cluster groups]] before connecting. 

To learn about launching GUI applications on DARWIN, refer to [[abstract:darwin:runjobs:schedule_jobs#launching-gui-applications-x11-forwarding|Schedule Jobs]] page.

==== Logging on to DARWIN for UD Allocation Users ====
Users with an UD allocation award should use SSH to connect to the DARWIN login node. For example, to connect to DARWIN with account ''traine'', type:

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

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

You may set up direct SSH key authentication on DARWIN 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 DARWIN directly by running ''ssh darwin.hpc.udel.edu''. 

==== Logging on to DARWIN for ACCESS (XSEDE) Allocation Users ====

ACCESS users with an allocation award on DARWIN will not be able to login until their password is set by using the password reset web application at [[https://idp.hpc.udel.edu/access-password-reset/]].

The application starts by directing the client to the CILogon authentication system where the "ACCESS CI (XSEDE)" provider should be selected.  If successful (and the client has an account on DARWIN), the application next asks for an email address to which a verification email should be sent; the form is pre-populated with the email address on-record on DARWIN for the client's account.  The client has 15 minutes to follow the link in that email message to choose a new password.  The form displays information regarding the desired length and qualifications of a valid password.  If the new password is acceptable, the client's DARWIN password is set and SSH access via password should become available immediately.

<WRAP center round tip 60%>
ACCESS users on DARWIN can use the [[https://idp.hpc.udel.edu/access-password-reset/|password reset web application]] to reset a forgotten password, too.
</WRAP>

For example to connect to DARWIN with account ''xsedeu1234'', type:

<code bash>
    ssh xsedeu1234@darwin.hpc.udel.edu
</code>

or if you need you use X-Windows requiring X11 forwarding, then use
<code bash>
    ssh -Y xsedeu1234@darwin.hpc.udel.edu
</code>

=== Installing an SSH Public Key ===

You may set up direct SSH key authentication on DARWIN 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.  You will need to do this if you need to use X11 tunneling and/or forwarding required for such applications like Jupyter Notebook.

The standard methods documented for adding a public key on DARWIN will only work once a password has been set for your ACCESS DARWIN account using the [[https://idp.hpc.udel.edu/access-password-reset/|password reset web application]].

The following pages may be helpful for users who are new to key-based SSH authentication:

  * [[https://www.linode.com/docs/guides/use-public-key-authentication-with-ssh/]]

==== Once you are logged into DARWIN ====
 
Once you are logged into DARWIN, your account is configured as a member of an allocation [[abstract:darwin:app_dev:compute_env#using-workgroup-and-directories|workgroup]] which determines access to your HPC resources on DARWIN. Setting your allocation workgroup is required in order to submit jobs to the DARWIN 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:darwin:app_dev:compute_env#startup-and-logout-scripts|startup and logout scripts]] and [[abstract:darwin: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 DARWIN. Use the <html><span style="color:#ffffff;background-color:#2fa4e7;padding:3px 7px !important;border-radius:4px;">sidebar</span></html> to navigate documentation about DARWIN, 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.

<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.