Linux Compute Servers

The following linux servers are available for general and/or computational use. These servers are available for public use via ssh, and have access to the same software suite as the Linux desktop machines.

Please be aware that GPU nodes are reserved for GPU work only. Any longer running jobs or processes found on GPU nodes that are not utilizing GPU resources is subject to termination.

Legacy servers are built around the Helios environment which utilizes Springdale Linux 7.

Each machine has local disk space in /tmp. This disk space can be written to by anyone, but you can only delete your own files. Create a directory in your name in the directory to organize your files more efficiently. Additionally, several servers also have access to our parallel filesystem.

When running more than one job on multiple servers, you should run additional jobs at lower priority.

Updating SSH keys

Periodically, we upgrade the operating systems on the compute servers to the latest major revision level (from 7.9 to 8, for example). When we do this, we do a "clean install" of the operating system, which results in new SSH keys on the compute servers. When this happen and you try to ssh into the system, you'll get an ominous looking error warning of a "man-in-the-middle" attack. It will look something like this:

$ ssh remus.sns.ias.edu
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
2d:4f:f2:c2:b0:96:c0:64:f9:f3:1f:63:5e:01:3a:34.
Please contact your system administrator.
Add correct host key in /home/prentice/.ssh/known_hosts to get rid of this message.
Offending key in /home/prentice/.ssh/known_hosts:266
RSA host key for remus.sns.ias.edu has changed and you have requested strict checking.
Host key verification failed.

Normally, this is bad. In this case, however, this is expected. In order to fix, do the following.

1. In your home directory, go into the directory ".ssh", and open the file known_hosts using a text editor. You MUST use a plain-text editor, NOT a word processor.

On Linux, I recommed Vi or Emacs. On Windows, you should use Notepad. If you're using a Mac, you should open a terminal, cd into the .ssh directory, and then use vi to edit the file.

2. Search for the line containing the hostname of the system you are trying to connect to. This line will begin with the hostname, possibly followed by the IP address of that host, and then a long string of characters, like this:

remus.sns.ias.edu,172.16.18.33 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAxyZKT6AdS/etI
K+rhrfgE4duyW7YskPyqjaED1A6BeBFDxNXnfFAeulCYZ238dUdw3scOD0PQz0Wr7furCV/cHGOolQbn
g2X0g0ye4qvtWejTddMTZKL7oTDYdc+cYnXvuVFs2jtxLPUfCaqbcwkSUb0DNl/c1cJmEvCM+Jzpdwf9
L9hC63ZDAV5t6UzyjNHp2BrSKmXfPdRlNGB1rBxWD9b3GTceUlEDZa61pUZm6JNaLqnuL2uVJ8OKTEnG
/gdXk4sXioOsdUHpGojyfI3K3bcB7xL+i1w2m2/Q8vEvJX0zUGlFIhbwMA96U/Fr/YuWx6a2u8LXAtl4
JF7YT8v+Q==

Note that the above key is really all one line, but is linewrapped for display purposes, and will almost definitely be linewrapped in your editor, too.

3. Delete that line and save the file.

4. Now ssh to the server again. Since you no longer have a key for that host in your known_hosts file, you'll get an informational message and prompt, like this:

$ ssh remus.sns.ias.edu
The authenticity of host 'remus.sns.ias.edu (172.16.18.33)' can't be established.
RSA key fingerprint is 2d:4f:f2:c2:b0:96:c0:64:f9:f3:1f:63:5e:01:3a:34.
Are you sure you want to continue connecting (yes/no)?

5. Type "yes" here. This will automatically add the public key for that host to your known_hosts files and allow to connect to the host.

That's it. That's all there is to it!Feb 14, 2020