Basics of Running Moss

This page shows the basic steps for running Moss. Your course may have scripts that combine these steps.

Step 1: Put files somewhere in the course account

Put the files that Moss should check somewhere in the course account. Contact CSCF if you don't have access. Place the files in a folder that contains a folder for each student, like this:

files_to_check
 |- yc2lee
 |   |- helper.cc
 |   |- mycode.cc
 |- omnafees
 |   |- mycode.cc
 |- fhgunn
 |   |- test.cc
 |   |- main.cc

Do not include any files that you do not want Moss to check. Moss will compare files even if the filenames are different.

Step 2: Run Moss

SSH into your course account on linux.student.cs.uwaterloo.ca.

Run Moss using the RunMoss script. Example:

yes O | /u/isg/bin/runMoss -d path/to/files_to_check '-l ascii'

Replace path/to/files_to_check with the path to the folder you made in Step 1. The yes O tells runMoss to process folders for students that aren't enrolled in your class; if you leave it out, you'll get a prompt for any folders that aren't for a student in your class.

The '-l ascii' part contains extra options for Moss. Put these extra options inside a pair of quotes. Extra options include:

• -l language: Specifies the language. It's recommended you try the ascii language, and also try the actual language of your assignment if available. Language options include: c, cc, java, python and more in moss.pl below
• -b path/to/basefile: Specifies a base file. Moss will try to ignore checking code that's in the basefile. You can have multiple -b for multiple basefiles.
• -m N: The -m option sets the maximum number of times a given passage may appear before it is ignored. A passage of code that appears in many programs is probably legitimate sharing and not the result of plagiarism. For assignments with short solutions, you may want to experiment with -m 3 or -m 4

More details on the extra options are in the file /u/cs_build/moss/moss.pl.

If you see an error like runMoss_impl: command not found then your course account doesn't have access to the Moss scripts. Please contact CSCF with your course number to get access.

Step 3: Check Moss results

RunMoss will create a folder called html. Go in and open index.html in a web browser to view the results. Instructions on mounting course accounts is on WebHome, accessing course accounts section.

Optional: If you find the results hard to read, you can run MossMakeReadable on the index.html:

moss_makereadable index.html 15 > readable.html

This command will create a file readable.html with some nicer formatting. The optional 15 makes it only show pairs where at least one student matches 15% or more.

Some caveats:

• Moss is not perfect. It can't catch all cheaters, nor is every case caught actually a cheating case. Think of Moss as an aid rather than a perfect tool. Someone on your course must manually review the cases.
• Moss was created by Standford, who gave UW CS the Moss executable at /u/cs_build/moss/moss. Nothing is sent to Standford's server when Moss is run. Moss is closed sourced, and CSCF cannot modify it or reverse engineer it, although the research paper is available.