32 A Unix directory might look as follows:

    33 

    34 \begin{center}

    35 \begin{verbatim}

    36 $ ls -ld . * */*

    37 drwxr-xr-x 1 ping staff  32768 Apr  2 2010 .

    38 -rw----r-- 1 ping students  31359 Jul 24 2011 manual.txt

    39 -r--rw--w- 1 bob students   4359 Jul 24 2011 report.txt

    40 -rwsr--r-x 1 bob students 141359 Jun  1 2013 microedit

    41 dr--r-xr-x 1 bob staff  32768 Jul 23 2011 src

    42 -rw-r--r-- 1 bob staff  81359 Feb 28 2012 src/code.c

    43 -r--rw---- 1 emma students    959 Jan 23 2012 src/code.h

    44 \end{verbatim}

    45 \end{center}

    46 

    47 with group memberships assigned as follows:

    48 \begin{center}

    49 \begin{tabular}{ll}

    50 Members of group staff: & ping, bob, emma\\ 

    51 Members of group students: & emma\\

    52 \end{tabular}

    53 \end{center}

    54 

    55 The file microedit is a text editor, which allows its users to open, edit and 

    56 save files. Note carefully that microedit has set its setuid flag. 

    57 Fill in the access control matrix below that shows for each of the above five files, 

    58 whether ping, bob, or emma are able to obtain the right to read (R) or replace (W) its 

    59 contents using the editor microedit.\bigskip

    60 

    61 \begin{center}

    62 \begin{tabular}{r|c|c|c|c|c}

    63         & manual.txt & report.txt & microedit & src/code.c & src/code.h \\\hline

    64 ping & & & & &\\\hline

    65 bob & & & & &\\\hline

    66 emma   & & & & &\\

    67 \end{tabular}

    68 \end{center}