Unix and Linux Services
Contents
Student and Faculty Use Servers
The CS Department provides a Linux server for use by CS students and staff. Please read the following to learn how to connect to it.
You must be connected to the CS VPN to connect!
The address for the Linux server is kept internal to the CS network, so you must connect to our VPN before attempting to connect via ssh.
Instructions for connecting to the CS VPN can be found at (VPN Services)
To learn how to connect to this server by ssh, please visit the SSH Access page.
Linux Servers
linux.cs.odu.edu may be used to connect to our services.
If you want to connect to a specific public linux server within the cluster, you may connect to it directly. Their hostnames are listed below:
callisto.cs.odu.edu
europa.cs.odu.edu
ganymede.cs.odu.edu
io.cs.odu.edu
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>
Replacing <hostname> with the the host for which you received the error, for example sol.cs.odu.edu and then reconnect. You may verify the given ECDSA fingerprint by comparing it to:
SHA256:Q2Y/JHxDJbvNITVsGpUITCZCn6zIpGXkj2v9fNa2gE4
If you are using PuTTY, simply click the yes button on the popup to update the cache of host keys and complete 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 c6:2f:cb:83:fc:b2:cf:4d:43:aa:1b:dc:43:23:80:fe
Home Directory
When you log in to your Unix account, you are placed in your "home directory" (/home/$USER). This will be the main working directory every time you log in.
Your home directory is backed up so it is advised to keep your data here. What is more, your home directory is available as your Windows Z-Drive, when connected to the CS network.
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.
Submitting cron jobs to the public Linux cluster
This is an explanation of how submitting cron jobs on our public Linux cluster (linux.cs.odu.edu) works.
This explanation applies to the following hosts:
callisto.cs.odu.edu
europa.cs.odu.edu
ganymede.cs.odu.edu
io.cs.odu.edu
When you add a cron job to your crontab on one of the hosts in the cluster, by default that job will run on every host in the cluster.
If you want a job to only run on one host you can prefix your job with /usr/bin/rcron. This system has failover so if multiple hosts in the cluster go down as long as there is one host up your job will continue to run.
A job using rcron looks like this:
12 11 * * * /usr/bin/rcron myjob
If you want to run jobs on a specific host, you should do some sort of hostname checking in a script so that it will only run on the specific host that you want it to.
SFTP Services
All files in your home directory can be access via an SFTP connection. To learn more, visit the SFTP Services page.
