The Linux Programming Interface

1430 Appendix F

processes. All four processes carry on to execute the next fork(), each creating a

further child. Consequently, a total of seven new processes are created.

24-2. A solution is provided in the file procexec/vfork_fd_test.c in the source code

distribution for this book.

24-3. If we call fork(), and then have the child call raise() to send itself a signal such as

SIGABRT, this will yield a core dump file that closely mirrors the state of the parent at

the time of the fork(). The gdb gcore command allows us to perform a similar task for

a program, without needing to change the source code.

24-5. Add a converse kill() call in the parent:

if (kill(childPid, SIGUSR1) == -1)

errExit("kill")

And in the child, add a converse sigsuspend() call:

sigsuspend(&origMask); /* Unblock SIGUSR1, wait for signal */

Chapter 25

25-1. Assuming a two’s complement architecture, where –1 is represented by a bit

pattern with all bits on, then the parent will see an exit status of 255 (all bits on in the

least significant 8 bits, which are all that is passed back to the parent when it calls

wait()). (The presence of the call exit(–1) in a program is usually a programmer error

resulting from confusion with the –1 return used to indicate failure of a system

call.)

Chapter 26

26-1. A solution is provided in the file procexec/orphan.c in the source code distribution

for this book.

Chapter 27

27-1. The execvp() function first fails to exec the file xyz in dir1, because execute

permission is denied. It therefore continues its search in dir2, where it successfully

execs xyz.

27-2. A solution is provided in the file procexec/execlp.c in the source code distribution of

this book.

27-3. The script specifies the cat program as its interpreter. The cat program “interprets”

a file by printing its contents—in this case with the –n (line numbering) option

enabled (as though we had entered the command cat –n ourscript). Thus, we would

see the following:

1 #!/bin/cat -n

2 Hello world

27-4. Two successive fork() calls yield a total of three processes related as parent, child,

and grandchild. Having created the grandchild process, the child immediately

exits, and is reaped by the waitpid() call in the parent. As a consequence of being