Courses & Instruction Using the NeXT Clusters


Campus Computing · University of Missouri - Columbia · 200 Heinkel Building · 314-882-2000

Update 16 August 1994 by ccpaulh@missouri.edu. Subject to change!

This document is directed mainly to instructors, explaining resources particularly related to instructional use of the MU NeXT computer systems. There are also some technical notes to system administrators regarding course accounts and ªhomeworkº directories.

Student Accounts: Inform the NeXT Coordinator or the Campus Computing Help Desk if you would like each student enrolled in a given course to automatically be pre-allocated a userid and password on the NeXT systems. An alternative for classes with fewer than twelve students is to simply have them request a userid from the Lab Assistant at the NeXT site.

Staff and Course Accounts: Generally, each person and each course should have separate accounts. Individual ªstaffº accounts can be arranged with the site Lab Assistant or User Consultant; course accounts should be requested from the NeXT Coordinator. The NeXT Coordinator also can work with the instructor to help organize use of the system, to schedule special training sessions, obtain handouts, etc.

File Access Permissions: On a Unix system, your access to each file and directory is controlled by three things: your userid, the Unix groups to which you belong, and the permissions set on the individual file or directory. On the MU public NeXT systems, when one creates a new file the default is for it to be readable or writeable only by the user, not by any others. This default is appropriate for students and other individualists; if you create many documents to be read by others you may want to change this default.

(NeXT's out of the box allow read-access by all. One can change the default protection of new files via the Preferences ªclock/calendarº Unix Expert panel, and by the ªset umaskº statement in file ~/.cshrc. One can change the permissions for existing files with the File Viewer, by clicking on the file (or shift-click for multiple files), and clicking the ªToolsº ªInspector...º menu. In a Unix shell, this is done by the chmod and chown commands.)

Submissions and GradedHomework 1: The Instructor's View:

One can define special directories to which students can copy their homework submissions and pick up the graded results, such that they cannot see the content of other students' submissions, though they can see the names of other student's files in such special directories. For a course with a single section, these directories are typically called ªSubmissionsº and ªGraded.Homeworkº. If a course has multiple sections, the convention has been to identify each section and directory a little redundantly:

/LocalLibrary/CourseInfo/ math175/WS94/08:40.Section/ 08:40.Submissions/ 08:40.Graded.Homework/ .... /LocalLibrary/CourseInfo/ math175/WS94/09:40.Section/ 09:40.Submissions/ 09:40.Graded.Homework/ ...etc... Simply creating such files is not enough! They must be given approriate permissions, and a made known to a special program. Contact the NeXT Co-ordinator to do this! You must identify: the course, times or numbers of multiple sections, and userids of all instructors or graders who are to have access to all files in Submissions or Graded.Homwork.

The special program (ªsubfixº) runs every 15 minutes and sets all files in such directories to appropriate permissions. If you should happen to access a file between the time a student submits it and the time subfix runs, then you will probably be able to only read it or copy it, not modify or delete it.

You must work with the original file the student submitted, not a copy, if you intend to eventually move it to the Graded.Homework directory. If you were to put a copy of this file in Graded.Homework rather than a modified version of the original, the student would not be able to read the copy.

The long form of the file viewer menu (obtained by pressing Command-Shift-L) should show the owner's userid such as c543210--useful if the file name is not sufficiently identifying. Note the group should be the group name associated with the course, such as math or math175. The subfix program sets the file permissions so that both the owner and members of the group can read and write the file, but others can't access it.

It's a good idea to test this facility from a userid not in the instructor/grader group before telling students to use it.

This facility discourages plagiarism but does not eliminate it.

Submissions and GradedHomework 2: The Student's View:

Students should name homework files to contain their student number (or name if the instructor agrees and there will not likely be collisions); for example, ªAngela.Anderson.Assignment.1º or ª543210.Homework.1.maº.

Drag the appropriate directory such as ª08:40.Submissionsº to the File Viewer shelf for easy access. Then, to submit some file, simply drag its icon to the ª08:40.Submissionsº directory/folder. A typical Submissions directory appears with a door icon; the door opens when a file is dragged to it.

Submissions and GradedHomework 3: The Sysadmin's View:

In fundamental terms, here's what we're trying to do:

This facility utilizes the Unix ªsticky bitº to set the group name when a file is dragged to a Submissions directory. A Graded.Homework directory is also writeable, so that the student can remove files belonging to him or her. See man pages for sticky and chmod.

The second thing that makes this work is the shell script /usr/local/etc/subfix which reads file /usr/local/etc/subfix.dirs, a list of all directories to be processed by subfix.

Requirements for each ªSubmissionsº or ªGraded.Homeworkº directory:

Entry in /etc/crontab.local might invoke subfix as:

0,15,30,45 * * * * root /usr/local/etc/subfix

Training

For materials that can be used to provide a general introduction to using the NeXT see other items in /LocalLibrary/Mizzou_Info, particularly 01_Welcome3.rtf


Questions and comments concerning these policies should be directed to the NeXT Lab site consultant or the MU Campus Computing "NeXT Lab Co-ordinator", 882-5000.