CS810D Advanced Programming in the UNIX Environment
Quiz 1


FULL NAME                       ______________________________________


USERNAME                        ______________________________________


1)  Which of the following is NOT (normally) found in the inode information:
    (3 points)

a)  timestamp of file creation
b)  file name
c)  pointer to parent directory
d)  pointer to next file in directory
e)  all of the above
d)  none of the above


Correct answer: (e) all of the above



2)  Consider the following directory listing:

$  ls -laR
total 32
drwxrwxrwt   3 jschauma  wheel   512 Sep 23 14:15 .
drwxrwxrwt  22 root      wheel  5632 Sep 20 22:02 ..
drwx------   2 jschauma  wheel   512 Sep 23 14:16 d
prw--w----   1 jdoe      wheel     0 Sep 16 15:34 fifo
lrwx------   1 jschauma  wheel     4 Sep 16 15:34 notalifo -> fifo
----------   1 jschauma  wheel     0 Sep 16 15:33 null

./d:
total 16
drwx------  2 jschauma  wheel  512 Sep 23 14:16 .
drwxrwxrwt  3 jschauma  wheel  512 Sep 23 14:15 ..
-rw-rw-rw-  1 jschauma  wheel    0 Sep 23 14:14 blah
-rw-------  1 jdoe      wheel    0 Sep 23 14:16 mottle


2.1)  The following people may remove the file 'null':

a) "jschauma"
b) "jdoe"
c) "root" / superuser
d) anybody in the group 'wheel'
e) anybody
f) nobody


Correct answer: (a) and (c)  (note sticky bit on the directory)

2.2)  The following people may read the file 'null':

a) "jschauma"
b) "jdoe"
c) "root" / superuser
d) anybody in the group 'wheel'
e) anybody
f) nobody

Correct answer: (c)
I would have accepted (a) and (c) if you noted that jschauma being the
owner of the file could change permissions such that he can read the file.


2.3)  The following people may modify the file 'notalifo':

a) "jschauma"
b) "jdoe"
c) "root" / superuser
d) anybody in the group 'wheel'
e) anybody
f) nobody

Correct answer: (a) and (c)


2.4)  The following people may remove the file 'd/blah':

a) "jschauma"
b) "jdoe"
c) "root" / superuser
d) anybody in the group 'wheel'
e) anybody
f) nobody

Correct answer: (a) and (c)


2.5)  The following people may remove the file 'd/mottle':

a) "jschauma"
b) "jdoe"
c) "root" / superuser
d) anybody in the group 'wheel'
e) anybody
f) nobody

Correct answer: (a) and (c)
'jdoe' cannot remove the file because the directory is owned by jschauma.

3.)  Consider the following permissions on the file:

-r-s--x--x  1 root  wheel  1234 Sep 23 15:00 oink

     This executable contains the call 'access("oink", W_OK|X_OK)'.
     What will it return? (3 points)

     Correct answer:  -1  (the file does not have write permissions for
                           'other' (or anybody for that matter))


4.)  Consider the following code:

	if ( creat("bar", S_IRUSR | S_IWUSR | S_IXUSR |
			  S_IRGRP | S_IWGRP |
			  S_IROTH | S_IWOTH) == -1 ) {
		perror("create error for bar");
		exit(1);
	}

     If the user runs the command

     umask 172

     before running this program, what will be the permissions on the file
     "bar"?  (3 points)


    Solution: The creat call asks for permissions 766, umask turns off
              exec for owner, all for group and write for other, so we end
              up with permissions 604 or "rw----r--".


5.)  Give two different methods of determining the current size of a file,
     with brief code examples in C. (3 points for each correct solution)

Solution:
  I) lseek to end of file

	if ((fdesc = open("/path/to/file", O_RDONLY)) == -1) {
                fprintf(stderr, "%s: Can't open file: %s\n",
                                        argv[0], strerror(errno));
                return 1;
	}

        if ((n = lseek(fdesc, 0, SEEK_END)) == -1) {
                fprintf(stderr, "%s: Can't seek to end: %s\n",
                                        argv[0], strerror(errno));
                return 1;
        }
        printf("File contains %d bytes\n", n);


  II) stat the file:

        struct stat sb;
        int n;

        if ((n = stat("/path/to/file", &sb)) == -1) {
                fprintf(stderr, "%s: Can't stat the file: %s\n",
                                        argv[0], strerror(errno));
                return 1;
        }
        printf("File contains %d bytes\n", (int)sb.st_size);