Unix and Linux Services

Student and Faculty Use Servers

The CS Department provides both Linux servers for use by CS students. To learn how to connect to these servers, please visit the SSH Access page.

Linux Servers

linux.cs.odu.edu may be used to connect to the load-balanced linux cluster.

The old records atria.cs.odu.edu and sirius.cs.odu.edu will also take users to the new load-balancer (if your ssh client returns an error while doing so, refer to 'Host Key Checking Failed' below).

The individual servers are:

canis.infra.cs.odu.edu

betelgeuse.infra.cs.odu.edu

aspidiske.infra.cs.odu.edu

scorpii.infra.cs.odu.edu

If required a specific cluster-member can be reached using the following mapping of different ports on the linux.cs.odu.edu record.

canis -> ssh linux.cs.odu.edu -p 1025 -l <username>

betelgeuse -> ssh linux.cs.odu.edu -p 1026 -l <username>

aspidiske -> ssh linux.cs.odu.edu -p 1027 -l <username>

scorpii -> ssh linux.cs.odu.edu -p 1028 -l <username>

Common Questions or Issues

Host Key Checking Failed

Problem

When our linux services recently migrated to a cluster of servers, the host keys associated with them changed. As a result, students who previously used ssh may receive one of the below error messages in their client since the migration:

In most linux environment using OpenSSH: 'Warning: Possible DNS Spoofing Detected!'

Using PuTTY on Windows: a popup saying 'Warning - Potential Security Breach!'

This is because your client is expecting the previous host key and not the new one. When this mis-match occurs, most ssh-clients by default refuse to complete the connection without intervention for security reasons.

Solution

If you are on linux using OpenSSH, the simplest solution is to remove the old host key: ssh-keygen -R <hostname> (replace <hostname> with the the host for which you received the error, for example atria.cs.odu.edu) and then reconnect. You may very the given ECDSA fingerprint by comparing it to:

SHA256:HQWL0W9pLzUVVO3VHcOteOD57ekvhQ9QCeOpIpDPWKQ

If you are using PuTTY, simply click the yes button on the popup to update the cache of host keys and continue the connection. You may verify the given ssh-ed25519 fingerprint by comparing it to:

The server's ssh-ed25519 key fingerprint is: ssh-ed25519 255 85:da:8e:d8:16:2c:70:93:64:5c:cc:f2:64:06:a3:8c

Cronjobs

The new servers share crontab between all servers in the cluster. This means that by default a cronjob set on one server will run on all four. If you want your cronjob to run on only a specific server you can preface the job with control statements:

[ "$(hostname)" != "scorpii" ] || echo "this is a command"

Which would result in this cronjob running on scorpii only.

Home Directory

When you log in to your Unix account, you are placed in your "Unix home directory". This will be the main working directory every time you log in. You can create and keep sub-directories,files and other important data in this directory.

Your home directory is backed up so it is advised to keep your data here. What is more, your Unix home directory gets mapped as your Windows Z-Drive so that you can share data between operating systems. Your Z-Drive can also be mapped to Apple Mac machines. To learn how you can do this, visit the Z-Drive Mac page.

Unix Permissions

Your security is important to us, and it should be very important to you. When you create files in your Unix home directory, you should be aware of the permissions you can set on these files. These permissions will determine whether or not your information can be viewed by other students in the department.

To understand how you can correctly set Unix permissions, please view the Unix Permissions page.

FTP Services

All files in your home directory can be access via FTP connection. To learn more, visit the FTP Services page.