Virtual Exam

Please read documentation: virtual exam

In summary, logging into <class_account>vx e.g. cs1234vx starts the exam. The exam files are located in <class_account>exam e.g. cs1234exam, follow (symbolic link) currentexam. You have ssh access to both these accounts if you have ssh access to the corresponding class account.

Useful scripts

• ~give/stable/bin/prac-install-vx [from_prac] to_prac

  • set up a standard virtual exam environment in <class_account>exam

  • if from_prac != to_prac
    • copy from_prac from virtual directory if exists
    • copy from_prac from gaol directory otherwise
  • else
    • copy from_prac from gaol directory

    gaol above refers to the old old old exam environment.

• priv passwd

  • change the <class_account>vx password before and after the exam with this script

• priv chown wildcard

  • change ownership of work directories from 90<uid> to exam account at the end of the exam to access the students' files

  • note that after changing ownership, students can't start the exam

    marimba % ls -la exams/19T1midterm/work
    total 16
    drwxrwxrwt  4 en1811exam en1811exam 4096 Mar 14 21:19 .
    drwxr-x---  6 en1811exam en1811exam 4096 Mar 12 17:50 ..
    drwxrws--- 14     929389 en1811exam 4096 Mar 14 21:36 z5016573
    drwxrws--- 13     906444 en1811exam 4096 Mar 12 20:02 z8470184

• /home/vxconf/vx.conf.d is the repository for vx.conf files for commonly used products e.g. gcc, python, gedit, fluxbox

  • prac-install-vx creates ~/exams/<prac>/etc/vx.conf.d and fill it with symbolic links to vx.conf files in /home/vxconf/vx.conf.d

  • remove any sym links not needed. exam takes less time to start up if there are less software.

    -rw-r--r-- 1 vxconf vxconf  433 Mar 14 21:31 000-header.conf
    -rw-r--r-- 1 vxconf vxconf  220 Mar 14 21:31 100-basicx.conf
    -rw-r--r-- 1 vxconf vxconf  159 Mar 14 21:31 100-fontconfig.conf
    -rw-r--r-- 1 vxconf vxconf   99 Mar 14 21:31 100-rxvt.conf
    -rw-r--r-- 1 vxconf vxconf  202 Mar 14 21:31 200-wm-fluxbox.conf
    -rw-r--r-- 1 vxconf vxconf  351 Mar 14 21:31 200-wm-fvwm.conf
    -rw-r--r-- 1 vxconf vxconf  608 Mar 14 21:31 300-interp-perl.conf
    -rw-r--r-- 1 vxconf vxconf  210 Mar 14 21:31 300-interp-pylint.conf
    -rw-r--r-- 1 vxconf vxconf 1894 Mar 14 21:31 300-interp-python.conf
    -rw-r--r-- 1 vxconf vxconf  860 Mar 14 21:31 300-toolchain-binutils.conf
    -rw-r--r-- 1 vxconf vxconf 3374 Mar 14 21:31 300-toolchain-clang.conf
    -rw-r--r-- 1 vxconf vxconf 1690 Mar 14 21:31 300-toolchain-gcc.conf
    -rw-r--r-- 1 vxconf vxconf  105 Mar 14 21:31 300-toolchain-gdb.conf
    -rw-r--r-- 1 vxconf vxconf   79 Mar 14 21:31 300-toolchain-make.conf
    -rw-r--r-- 1 vxconf vxconf  212 Mar 14 21:31 300-toolchain-valgrind.conf
    -rw-r--r-- 1 vxconf vxconf   84 Mar 14 21:31 400-browser-firefox.conf
    -rw-r--r-- 1 vxconf vxconf   54 Mar 14 21:31 400-browser-midori.conf
    -rw-r--r-- 1 vxconf vxconf  369 Mar 14 21:31 400-browser-nautilus.conf
    -rw-r--r-- 1 vxconf vxconf   84 Mar 14 21:31 400-viewer-evince.conf
    -rw-r--r-- 1 vxconf vxconf  110 Mar 14 21:31 400-viewer-xpdf.conf
    -rw-r--r-- 1 vxconf vxconf  328 Mar 14 21:31 500-editor-emacs.conf
    -rw-r--r-- 1 vxconf vxconf  300 Mar 14 21:31 500-editor-gedit.conf
    -rw-r--r-- 1 vxconf vxconf   52 Mar 14 21:31 500-editor-idle.conf
    -rw-r--r-- 1 vxconf vxconf   47 Mar 14 21:31 500-editor-nedit.conf
    -rw-r--r-- 1 vxconf vxconf   96 Mar 14 21:31 500-editor-spyder3.conf
    -rw-r--r-- 1 vxconf vxconf   26 Mar 14 21:31 500-editor-vi.conf
    -rw-r--r-- 1 vxconf vxconf  161 Mar 14 21:31 500-editor-vim.conf

    thanks to Jashank for the original idea

Problems - Tips on how to solve

• ensure that multiple logins are possible without files in the work directory being clobbered. use "cp -n" or "tar --keep-newer-files" or "unzip -n"

• when the exam crashes after you authenticated with your zid, check stderr.log file under <exam_account>/var directory. Look at the latest directories.

  marimba % ls -lt ~/var | head -5
  total 988
  drwxr-xr-x 2 cs9024exam cs9024exam 4096 Feb 13 06:59 marimba-25528
  drwxr-xr-x 2 cs9024exam cs9024exam 4096 Feb 12 20:49 wagner-7800
  drwxr-xr-x 2 cs9024exam cs9024exam 4096 Feb 12 20:33 vx4-45795
  drwxr-xr-x 2 cs9024exam cs9024exam 4096 Feb 12 18:39 vx4-34624

• after changing ownership of the work directories (e.g. under /home/cs1234exam/currentexam/work), you can't start the exam with the same work directories.
  • create a new toplevel work directory.

    cd ~/exams/18s2supp
    mv work work.19dec
    mkdir work
    chmod 1777 work

  • or remove the student's work directory

    cd ~/exams/18s2supp/work
    priv chown z5555555
    rm -r z5555555

• path mounted on top of a previous mount cause the exam environment to abort on subsequent logins. The exam environment, on start, attempts to delete the old gaol if it exists by unmounting directories.

  vx08 % cat var/vx04-2104607/stderr.log
  umount: /var/gaol/meicheng/usr/lib/python3/dist-packages: not mounted.

  • To fix the problem above, umount "/var/gaol/meicheng/usr/lib" to allow the gaol to be removed and therefore the student to log in.
  • To remove the gaol manually:

    # umount /var/gaol/meicheng/usr/lib
    /home/virtualexam/bin/delete_gaol <studentid>

  • May need to remove any associated processes, look for user ID's equal to 900000 + the actual user ID.
  • The problem can be avoided by ensuring that a directory is not under [bind mounts] when its parent is already set to be mounted. Global bind mounts:

    [bind mounts]
    
    /lib
    /lib64
    /usr/lib
    /usr/share
    /usr/include
    /etc/ssl
    /etc/fonts
    /etc/alternatives