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linux_ssh_access [2020/09/01 17:57]
pgh5a
linux_ssh_access [2021/04/13 19:33]
pgh5a
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 All Linux servers run "​secure shell" - '​ssh'​. ​ Anyone with a CS account may log into these servers. ​ All Linux servers run "​secure shell" - '​ssh'​. ​ Anyone with a CS account may log into these servers. ​
  
-On Grounds, you can simply '​ssh'​ to CS servers ​typically by using a Terminal application like HyperTerm (Windows) or Terminal (Mac).+On Grounds, you can simply '​ssh'​ to CS servers.
  
-Off Grounds, you are not able to '​ssh'​ directly into CS servers.  However connections to ''​%%portal.cs.virginia.edu%%'' ​are allowed from off Grounds.+Off Grounds, you are not able to '​ssh'​ directly into most CS servers ​except ​''​%%portal.cs.virginia.edu%%''​.
  
 You must use your CS domain userid (identical to your UVA userid) and password to '​ssh'​ to portal. For example: You must use your CS domain userid (identical to your UVA userid) and password to '​ssh'​ to portal. For example:
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 ''​%%ssh -l abc1de portal.cs.virginia.edu%%''​. Alternatively,​ ''​%%ssh abc1de@portal.cs.virginia.edu%%''​ ''​%%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.+Most users on Mac or Windows ​PC will use a Terminal application like SecureCRTCmder, KiTTY, or Putty (Windows), Terminal or iTerm2 (Mac) to '​ssh'​ to our linux servers. 
 + 
 +Note that 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]] If you'd like to use a graphical windowing interface to department servers, see: [[nx_lab|NX Linux Remote Desktop Cluster]]
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-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.+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. Note that you should use the UVA "​Anywhere"​ VPN, not the "More Secure"​ VPN.
  
 === Option 2: Access via portal.cs.virginia.edu === === Option 2: Access via portal.cs.virginia.edu ===
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 </​code>​ </​code>​
  
-=== SSH Jumphost ​Options ​===+=== Jumphost ​Option ​===
  
-The OpenSSH ​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 manpages: +The ssh client has an option ''​%%-J%%''​ to specify a host 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) into one single command.
- +
-<​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%%''​ 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>​ <​code>​
-[abc1de@outside-uva ~]$ ssh -l abc1de gpusrv01 -J portal.cs.virginia.edu +[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@portal04.cs.virginia.edu'​s password: ​                 <-- first asked to authenticate to portal 
-abc1de@gpusrv01'​s password: ​                                             <-- immediately able to log into gpusrv01+abc1de@gpusrv01'​s password: ​                                 <-- immediately able to log into gpusrv01
 .... ....
 abc1de@gpusrv01 ~ $ abc1de@gpusrv01 ~ $
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 <​code>​ <​code>​
-username@portal01:​~$ ping portal03+abc1de@portal01:​~$ ping portal03
 PING portal03.cs.virginia.edu (128.143.67.43) 56(84) bytes of data. 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=1 ttl=64 time=0.149 ms
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 === From Linux/Mac OS === === From Linux/Mac OS ===
  
-To log into this server from another computer running Linux/​Unix/​MacOS,​ run the following from a shell:+To log into server from another computer running Linux/​Unix/​MacOS,​ run the following from a shell:
  
 <​code>​ <​code>​
-username@host ~ $ ssh username@gpusrv04.cs.virginia.edu +abc1de@host ~ $ ssh username@gpusrv04.cs.virginia.edu 
-username@gpusrv04'​s password: ​                             <- Enter Password+abc1de@gpusrv04'​s password: ​                             <- Enter Password
 ... ...
-[username@gpusrv04 ~]$+[abc1de@gpusrv04 ~]$
 </​code>​ </​code>​
  
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 === Servers === === Servers ===
  
-For a listing of generally available servers in CS, see the article [[compute_resources|General Purpose Nodes]]+For a listing of generally available servers in CS, see the article [[compute_resources|Computing Resources]]
  
 === Login Restrictions (Info for Faculty) === === 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.+We want to give all of our users fair and equal access to whatever computing resources we have to offer. ​We do not restrict ​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 === 
- 
-This section can be skipped over if your server has already been configured with login restrictions. 
  
 By default, access rules in ''​%%time.conf%%''​ are not used unless a //PAM module// (pluggable authentication module) is configured to read them.  This is done by adding a line to the ''​%%sshd%%''​ //PAM// module file.  ​ By default, access rules in ''​%%time.conf%%''​ are not used unless a //PAM module// (pluggable authentication module) is configured to read them.  This is done by adding a line to the ''​%%sshd%%''​ //PAM// module file.  ​
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 account ​            ​required ​               pam_time.so account ​            ​required ​               pam_time.so
 </​code>​ </​code>​
- 
-=== 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%%'':​
  
 <​code>​ <​code>​
-sshd;​*;​!root&​fls4t&ejs3s&pgh5a;​!Al0000-2400+sshd;​*;​!root&​abc1de&fgh1ij&klm1no;​!Al0000-2400
 </​code>​ </​code>​
  
-This line is formatted such that the users listed are separated by ampersand ''​%%&​%%''​ characters. ​ This entry will allow the users ''​%%root%%'',​ ''​%%fls4t%%'',​ ''​%%ejs3s%%''​ and ''​%%pgh5a%%''​ are allowed access. ​ **Be sure to always include yourself and root in this rule.  Failure to do so may result in everyone becoming locked out.**+This line is formatted such that the users listed are separated by ampersand ''​%%&​%%''​ characters. ​ This entry will allow the users ''​%%root%%'',​ ''​%%abc1de%%'',​ ''​%%fgh1ij%%''​ and ''​%%klm1no%%''​ are allowed access. ​ **Be sure to always include yourself and root in this rule.  Failure to do so may result in everyone becoming locked out.**
  
-If we wanted to add the user ''​%%ktm5j%%''​ to this rule above, we would insert the string ''​%%&​ktm5j%%''​ like this:+If we wanted to add the user ''​%%pqr1st%%''​ to this rule above, we would insert the string ''​%%&​pqr1st%%''​ like this:
  
 <​code>​ <​code>​
-sshd;​*;​!root&​fls4t&ejs3s&pgh5a&ktm5j;​!Al0000-2400+sshd;​*;​!root&​abc1de&fgh1ij&klm1no&pqr1st;​!Al0000-2400
 </​code>​ </​code>​
  
 Changes to this file take effect immediately,​ no services need to be restarted. ​ When editing this file, be sure that you keep at least one active ssh connection until you have tested your changes. ​ This will prevent becoming locked out if any errors are made! Changes to this file take effect immediately,​ no services need to be restarted. ​ When editing this file, be sure that you keep at least one active ssh connection until you have tested your changes. ​ This will prevent becoming locked out if any errors are made!
  • linux_ssh_access.txt
  • Last modified: 2021/04/13 19:34
  • by pgh5a