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--- linux_ssh_access [2019/01/02 11:40] – ktm5j
+++ linux_ssh_access [2025/09/08 12:21] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+===== Linux Server Access =====
+All Linux servers run "secure shell" (//ssh//).  Anyone with a CS account may log into the department's servers.
+Users on a Windows PC can use a Terminal application like //SecureCRT, Cmder, KiTTY, or Putty// to //ssh// to our servers.
+Users on a Mac can use an application like //Terminal// or //iTerm2// to //ssh// to our servers.
+If you'd like to use a graphical windowing interface to our servers, see: [[nx_lab|Nomachine Remote Desktops]]
+----
+===== On Grounds =====
+You can //ssh// to CS servers.
+Use your CS domain userid (identical to your UVA userid) and password to //ssh// to ''%%portal%%''. For example:
+''%%ssh -l abc1de portal.cs.virginia.edu%%''. Alternatively, ''%%ssh abc1de@portal.cs.virginia.edu%%''
+----
+==== Off Grounds: Option 1: VPN access ====
+Start a VPN session to UVA using the [[https://virginia.service-now.com/its?id=itsweb_kb_article&sys_id=f24e5cdfdb3acb804f32fb671d9619d0|UVA VPN]]. Once the VPN is established, you can //ssh// to CS servers directly. Note that you should use the UVA "Anywhere" VPN, not the "More Secure" VPN.
+----
+==== Off Grounds: Option 2: ssh to portal.cs.virginia.edu ====
+You can //ssh// directly into ''%%portal.cs.virginia.edu%%'' without having to use the UVA VPN.  Once you are logged into the ''%%portal%%'' cluster, you can then //ssh// to other CS servers. //Your username on the Mac or PC may be different from your CS/UVA userid. So be sure to include your CS/UVA userid on the ''ssh'' command line.//
+For example:
+<code>
+[abc1de@outside-uva ~]$ ssh abc1de@portal.cs.virginia.edu
+abc1de@portal.cs.virginia.edu's password:
+Last login: Mon Jul 29 14:12:10 2021
+abc1de@portal04 ~ $ hostname
+portal04                                               <-- you are logged into the portal cluster
+abc1de@portal04 ~ $ ssh gpusrv01                       <-- you can now ssh to gpusrv01
+abc1de@gpusrv01's password:
+abc1de@gpusrv01 ~ $                                    <-- you are logged into gpusrv01
+</code>
+----
+==== Jumphost Option ====
+The //ssh// command has an option ''%%-J%%'' to specify a server to use as a "jumphost" that lets you access other servers directly with one command.  This combines two steps (for example, //ssh// into //portal.cs.virginia.edu// and then //ssh// to //gpusrv01//).
+Here is how we use this option to "jump" from //portal// to another CS server.  Let's repeat the example of logging in to //gpusrv01//.
+<code>
+[abc1de@outside-uva ~]$ ssh abc1de@gpusrv01 -J abc1de@portal.cs.virginia.edu
+abc1de@portal04.cs.virginia.edu's password:                  <-- first asked to authenticate to portal
+abc1de@gpusrv01's password:                                  <-- immediately able to log into gpusrv01
+abc1de@gpusrv01 ~ $                                          <-- you are logged into gpusrv01
+</code>
+==== SSH Configuration for Jumphost ====
+You can also have a local configuration file with the following contents. This file is on your laptop or desktop
+  * On **Windows** this file is: ''%%C:\Users\<username>\.ssh\config%%''
+  * On **Linux/MacOS** this file is: ''%%~/.ssh/config%%''
+<code>
+Host *
+    ServerAliveInterval 60
+Host portal
+    HostName portal.cs.virginia.edu
+    User <userid>
+Host <CS server name>
+    HostName <CS server name>.cs.virginia.edu
+    User <userid>
+    ProxyJump portal
+</code>
+If you have an SSH keypair, you can specify it to be used for logging into a CS server. This requires that the public key contents be save in your CS home directory file ''%%~/.ssh/authorized_keys%%''
+<code>
+Host portal
+    HostName portal.cs.virginia.edu
+    User <userid>
+    IdentityFile /home/username/.ssh/id_ed25519
+</code>
+Then you can do the following
+<code>
+~$ ssh portal
+</code>
+----
+===== SSH Key Generation for Logging into Portal =====
+SSH keys can be generated and used for SSH authentication to CS login servers such as **portal**.
+To do this, start by generating a key. This can be done on your local computer by opening a terminal.
+=== 0.1: SSH for Linux & MacOS ===
+Application for running this command are **Terminal**
+=== 0.2: SSH for Windows ===
+Applications for running this commands are **Command Prompt** or **PowerShell**
+After opening the appropriate application, generate the key using one of the two options, replace ''%%<userid>%%'' with your **UVA computing ID**
+<code>
+~$ ssh-keygen -t ed25519 -C "<userid>@portal.cs.virginia.edu"
+OR
+~$ ssh-keygen -t rsa -b 4096 -C "<userid>@portal.cs.virginia.edu"
+</code>
+After doing so, you may be prompted for where to save the file to choose a non-default location, select **Enter** to use the path shown
+<code>
+Enter file in which to save the key (/home/username/.ssh/id_ed25519):
+</code>
+Then, you can choose to further protect your key with a passphrase, which is recommended to do
+<code>
+Enter passphrase (empty for no passphrase):
+Enter same passphrase again:
+</code>
+Then, you will see the following output
+<code>
+Your identification has been saved in /home/username/.ssh/id_ed25519
+Your public key has been saved in /home/username/.ssh/id_ed25519.pub
+The key fingerprint is:
+SHA256:AbCdEfg123456 <userid>@portal.cs.virginia.edu
+The key's randomart image is:
++--[ED25519 256]--+
+|        .        |
+|       + .       |
+|      . B .      |
+|     o * +       |
+|    X * S        |
+|   + O o . .     |
+|    .   E . o    |
+|       . . o     |
+|        . .      |
++----[SHA256]-----+
+</code>
+Referencing the above, two files are generated
+  - ''%%/home/username/.ssh/id_ed25519%%'', which is the **private key**, this is kept local to your computer
+  - ''%%/home/username/.ssh/id_ed25519.pub%%'', which is the **public key**, this is copied to CS servers
+After generating the key, you will need to copy the contents of the **Public Key to your home directory on CS servers**. In this example, we'll copy **/home/username/.ssh/id_ed25519.pub** to **/u/<userid>/.ssh/authorized_keys**.
+On **MacOS** and **Linux** you can use the following command, which requires entering your SSH password, replace ''%%<userid>%%'' with your **UVA computing ID**
+<code>
+~$ ssh-copy-id <userid>@portal.cs.virginia.edu
+</code>
+On **Windows**, you can run the following command in **Command Prompt** or **PowerShell**, replacing ''%%<username>%%'' with your local computer username, and replace ''%%<userid>%%'' with your **UVA computing ID**
+<code>
+C:\Users\<username>> type C:\Users\username\.ssh\id_ed25519.pub | ssh <userid>@portal.cs.virginia.edu "mkdir ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys"
+</code>
+Then, after copying the the public key contents, you can use the key to SSH into portal, entering the passphrase for the key (if one was used)
+<code>
+~$ ssh <userid>@portal.cs.virginia.edu
+</code>
+----
+===== Host Names depend upon your network connection =====
+If you are on the Computer Science network just use the hostname of a server (ex. //portal//). If you are outside of the CS network (on wireless for example), use the hostname's fully qualified name (FQDN) (ex. //portal.cs.virginia.edu//).
+----
+==== Available Servers ====
+For a listing of generally available servers in CS, see [[compute_resources|Computing Resources]]