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Linux Server Access
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).
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 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 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
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.
[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 ~ $
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:
-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.
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
[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 ~ $
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.
abc1de@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
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 a server from another computer running Linux/Unix/MacOS, run the following from a shell:
abc1de@host ~ $ ssh username@gpusrv04.cs.virginia.edu abc1de@gpusrv04's password: <- Enter Password ... [abc1de@gpusrv04 ~]$
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 SSH from Windows
Servers
For a listing of generally available servers in CS, see the article Computing Resources
Login Restrictions (Info for Faculty)
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.
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.
Add the following line to the file to the end /etc/pam.d/sshd
:
account required pam_time.so
Now that PAM is configured to read time.conf
we can now put in a rule. Here is an example rule from time.conf
:
sshd;*;!root&abc1de&fgh1ij&klm1no;!Al0000-2400
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 pqr1st
to this rule above, we would insert the string &pqr1st
like this:
sshd;*;!root&abc1de&fgh1ij&klm1no&pqr1st;!Al0000-2400
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!