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linux_ssh_access [2018/11/02 19:38]
ktm5j
linux_ssh_access [2020/09/01 17:58]
pgh5a
Line 1: Line 1:
-====== Linux SSH Access ​======+==== Linux Server ​Access ====
  
-Here in CS we want to give all of our users fair and equal access to whatever computing resources we have to offer. ​ For this reason we are discontinuing the practice of restricting login access to certain ​servers.  ​However, there are number of servers ​that still have access restrictions in place. ​ This article is to show users with ''​%%sudo%%''​ privileges how to edit ''​%%/​etc/​security/​time.conf%%''​ to allow user logins.+All Linux servers ​run "​secure shell" - '​ssh'​.  ​Anyone with CS account may log into these servers. ​
  
-===== Login Restrictions ​=====+On Grounds, you can simply '​ssh'​ to CS servers typically by using a Terminal application like HyperTerm (Windows) or Terminal (Mac). 
 + 
 +Off Grounds, you are not able to '​ssh'​ directly into CS servers. ​ However connections to ''​%%portal.cs.virginia.edu%%''​ are allowed from off Grounds. 
 + 
 +You must 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%%''​ 
 + 
 +Note that if you are opening a terminal application on your Mac or PC, your username on the Mac or PC may be different from your CS/UVA userid. So be sure to include your userid on the '​ssh'​ command line. 
 + 
 +If you'd like to use a graphical windowing interface to department servers, see: [[nx_lab|NX Linux Remote Desktop Cluster]] 
 + 
 +=== Access from off Grounds === 
 + 
 +**Use one of these options to access CS servers from outside of UVA.** 
 + 
 +=== Option 1: VPN access === 
 + 
 + 
 +If you are outside of the UVA network (off grounds) then you can first 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. 
 + 
 +=== Option 2: Access via 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. 
 + 
 +<​code>​ 
 +[abc1de@outside-uva ~]$ ssh -l abc1de portal.cs.virginia.edu 
 +abc1de@portal.cs.virginia.edu'​s password:  
 +Last login: Mon Jul 29 14:12:10 2019 
 +abc1de@portal04 ~ $ hostname 
 +portal04 ​                                              <​-- We are logged into portal cluster 
 +abc1de@portal04 ~ $ ssh gpusrv01 ​                        <​-- We can now access gpusrv01 
 +abc1de@gpusrv01'​s password: 
 +.... 
 +abc1de@gpusrv01 ~ $ 
 +</​code>​ 
 + 
 +=== Jumphost Option === 
 + 
 +The ssh client has an option ''​%%-J%%''​ to specify a host to use as a "​jumphost"​ that lets you access other servers directly, in one step.  This combines two steps (for example, ssh into portal.cs.virginia.edu and then ssh to gpusrv01) into one single command. ​ From the //man// page: 
 + 
 +<​code>​ 
 +     -J destination 
 +             ​Connect to the target host by first making a ssh connection to 
 +             the jump host described by destination and then establishing a 
 +             TCP forwarding to the ultimate destination from there. ​ Multiple 
 +             jump hops may be specified separated by comma characters. ​ This 
 +             is a shortcut to specify a ProxyJump configuration directive. 
 +             Note that configuration directives supplied on the command-line 
 +             ​generally apply to the destination host and not any specified 
 +             jump hosts. ​ Use ~/​.ssh/​config to specify configuration for jump 
 +             ​hosts. 
 +</​code>​ 
 + 
 +Here is how we use this option to "​jump"​ from portal.cs to another CS server. ​ Let's repeat the example of logging in to ''​%%gpusrv01%%''​ 
 + 
 +<​code>​ 
 +[abc1de@outside-uva ~]$ ssh -l abc1de gpusrv01 -J 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 ~ $ 
 +</​code>​ 
 + 
 +=== Server Domain Names === 
 + 
 +Computer Science hosts its own DNS server with authority over the ''​%%cs.virginia.edu%%''​ domain space. ​ Any server in CS will have a fully qualified domain name (fqdn) of ''​%%hostname.cs.virginia.edu%%''​. 
 + 
 +=== Short Names === 
 + 
 +If you are inside of the Computer Science network then use the hostname of a server instead of its fully qualified name.  For example, if you are logged into a CS server, you can ping another server by its hostname alone. 
 + 
 +<​code>​ 
 +username@portal01:​~$ ping portal03 
 +PING portal03.cs.virginia.edu (128.143.67.43) 56(84) bytes of data. 
 +64 bytes from portal03.cs.virginia.edu (128.143.67.43):​ icmp_seq=1 ttl=64 time=0.149 ms 
 +64 bytes from portal03.cs.virginia.edu (128.143.67.43):​ icmp_seq=2 ttl=64 time=0.123 ms 
 +</​code>​ 
 + 
 +This will not work from outside of the CS network unless you modify your DNS search path to contain ''​%%cs.virginia.edu%%''​. 
 + 
 +=== Login to other servers ​==
 + 
 +=== From Linux/Mac OS === 
 + 
 +To log into this server from another computer running Linux/​Unix/​MacOS,​ run the following from a shell: 
 + 
 +<​code>​ 
 +username@host ~ $ ssh username@gpusrv04.cs.virginia.edu 
 +username@gpusrv04'​s password: ​                             <- Enter Password 
 +... 
 +[username@gpusrv04 ~]$ 
 +</​code>​ 
 + 
 +In Mac OS the Terminal app can be found in the Utilities folder under Applications. 
 + 
 +=== From Windows === 
 + 
 +For information about SSH clients for Windows, see the article [[windows_ssh|SSH from Windows]] 
 + 
 +=== Servers === 
 + 
 +For a listing of generally available servers in CS, see the article [[compute_resources|General Purpose Nodes]] 
 + 
 +=== Login Restrictions (Info for Faculty) ​=== 
 + 
 +Here in CS we want to give all of our users fair and equal access to whatever computing resources we have to offer. ​ For this reason we are discontinuing the practice of restricting login access to certain servers. ​ However, there are a number of servers that still have access restrictions in place. ​ This article is to show users with ''​%%sudo%%''​ privileges how to edit ''​%%/​etc/​security/​time.conf%%''​ to allow user logins.
  
 There are several configuration files located in ''​%%/​etc/​security%%''​ on Linux servers. ​ In this directory, we can use ''​%%time.conf%%''​ to restrict ssh login to a specific set of user accounts. There are several configuration files located in ''​%%/​etc/​security%%''​ on Linux servers. ​ In this directory, we can use ''​%%time.conf%%''​ to restrict ssh login to a specific set of user accounts.
  
-==== PAM Setup ====+=== PAM Setup ===
  
 This section can be skipped over if your server has already been configured with login restrictions. This section can be skipped over if your server has already been configured with login restrictions.
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 </​code>​ </​code>​
  
-==== time.conf ​====+=== time.conf ===
  
 Now that //PAM// is configured to read ''​%%time.conf%%''​ we can now put in a rule.  Here is an example rule from ''​%%time.conf%%'':​ Now that //PAM// is configured to read ''​%%time.conf%%''​ we can now put in a rule.  Here is an example rule from ''​%%time.conf%%'':​
  • linux_ssh_access.txt
  • Last modified: 2020/10/06 12:48
  • by pgh5a