CSE 120: Troubleshooting Account Issues

Common account issues and tips to resolve them:

Prep not found

If you are logged in to an ieng6 server and you encounter problems prepping for CSE 120 (e.g., running "CSE120_FA25_A00" at the shell prompt returns an error), then first try logging out and logging back in. If you encounter the same error after logging back in a second time, contact ETS to troubleshoot your account. While waiting for a response from ETS, you can try to manually load the CSE 120 module as described below.

Module(s) not found: CSE120.... (or pending enrollment)

If your enrollment is still pending or if you encounter errors when running "CSE120_FA25_A00" at the shell prompt, then try explicitly running the following command: 

%  module load /home/linux/ieng6/CSE120_FA25_A00/public/modulefiles/CSE120_FA25_A00
Even if it prints out errors, it should still initialize your environment to use nachos.

Command not found

If you encounter an error of the form "nachos: command not found" or "submit-proj0: command not found", it indicates that your account has not been prepped for working for CSE 120. See the above two sections.

Disk quota exceeded

If you are working in your account on ieng6, either directly or via VS Code, and you encounter the error "disk quota exceeded", then your account has reached the limit on the amount of disk space you can use.

The culprit is almost always the VS Code file cache, which can consume hundreds of MBs of disk space. Since it is a cache, it is safe to delete it to free up disk space in your account: 

% rm -rf ~/.vscode-server

Class file has wrong version ..., should be ...

If you encounter an error of the form "class file has wrong version **.0, should be **.0", it usually indicates that the compiled Java .class files in your github repo were compiled with a different version of Java than the one installed on your system.

This situation typically happens when one person in a group compiles Nachos on their laptop (say) and commits and pushes the compiled .class files to github. Then another person in the group is logged in to ieng6 and pulls the updates to their local repo. If the versions of Java are different between the laptop and ieng6, then Java complains.

The problem is easy to fix: just delete the .class files in your local repo and recompile. For project 1, for instance, you can do the following: 

% cd nachos/proj1
% make clean
% make

Host key verification failed (ssh)

If you encounter an ssh error of the form: 

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    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 a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
SHA256:npmS8Gk0l+zAXD0nNGUxr7hLeYPn7zzhYWVKxlfNaeQ.
Please contact your system administrator.
Add correct host key in /[...]/.ssh/known_hosts to get rid of this message.
Offending RSA key in /[...]/.ssh/known_hosts:2
RSA host key for ieng6.ucsd.edu has changed and you have requested strict checking.
Host key verification failed.
Do not worry, it just means that the configuration for the ieng6 servers has changed. There are two options to fix the issue. Either use an editor like vim to delete the line in ~/.ssh/known_hosts that starts with ieng6.ucsd.edu (line 2 in the above example), or delete the ~/.ssh/known_hosts file and rebuild it from scratch as you ssh into more hosts again (easiest option).

VSCode ssh timeout

If you encounter an ssh error of the form, "ssh: connect to host hostname port 22: Connection timed out" when using ssh in VSCode, try any of the following:

Also remember that you can always work on the machines in the CSE basement.

voelker@cs.ucsd.edu