Exercises

8.1	In Figure 8.3, we said that replacing the call to _exit with a call to exit might cause the standard output to be closed and printf to return -1. Modify the program to check whether your implementation behaves this way. If it does not, how can you simulate this behavior?
8.2	Recall the typical arrangement of memory in Figure 7.6. Because the stack frames corresponding to each function call are usually stored in the stack, and because after a vfork, the child runs in the address space of the parent, what happens if the call to vfork is from a function other than main and the child does a return from this function after the vfork? Write a test program to verify this, and draw a picture of what's happening.
8.3	When we execute the program in Figure 8.13 one time, as in $ ./a.out the output is correct. But if we execute the program multiple times, one right after the other, as in $ ./a.out ; ./a.out ; ./a.out output from parent ooutput from parent ouotuptut from child put from parent output from child utput from child the output is not correct. What's happening? How can we correct this? Can this problem happen if we let the child write its output first?
8.4	In the program shown in Figure 8.20, we call execl, specifying the pathname of the interpreter file. If we called execlp instead, specifying a filename of testinterp, and if the directory /home/sar/bin was a path prefix, what would be printed as argv[2] when the program is run?
8.5	How can a process obtain its saved set-user-ID?
8.6	Write a program that creates a zombie, and then call system to execute the ps(1) command to verify that the process is a zombie.
8.7	We mentioned in Section 8.10 that POSIX.1 requires that open directory streams be closed across an exec. Verify this as follows: call opendir for the root directory, peek at your system's implementation of the DIR structure, and print the close-on-exec flag. Then open the same directory for reading, and print the close-on-exec flag.