Advanced Programming in the UNIX® Environment

ptg10805159

Appendix C Chapter 9 Solutions 923

8.6 The program in FigureC.10 creates a zombie.

#include "apue.h"

#ifdef SOLARIS

#define PSCMD "ps -a -o pid,ppid,s,tty,comm"

#else

#define PSCMD "ps -o pid,ppid,state,tty,command"

#endif

int

main(void)

{

pid_t pid;

if ((pid = fork()) < 0)

err_sys("fork error");

else if (pid == 0) /* child */

exit(0);

/* parent */

sleep(4);

system(PSCMD);

exit(0);

}

Figure C.10 Create a zombie and look at its status withps

Zombies areusually designated byps( 1 )with a status ofZ:

$./a.out

PID PPIDSTTCOMMAND

2369 2208Spts/2 -bash

7230 2369Spts/2 ./a.out

7231 7230Zpts/2 [a.out] <defunct>

7232 7230Spts/2 sh -c ps -o pid,ppid,state,tty,command

7233 7232Rpts/2 ps -o pid,ppid,state,tty,command

Chapter 9

9.1 Theinitprocess learns when a terminal user logs out, becauseinitis the

parent of the login shell and receives theSIGCHLDsignal when the login shell

terminates.

For a network login, however,initis not involved. Instead, the login entries in

theutmpandwtmpfiles, and their corresponding logout entries, areusually

written by the process that handles the login and detects the logout (telnetdin

our example).