The Linux Programming Interface

Process Groups, Sessions, and Job Control 713

int

main(int argc, char *argv[])

{

pid_t parentPid, childPid;

int j;

struct sigaction sa;

if (argc < 2 || strcmp(argv[1], "--help") == 0)

usageErr("%s {d|s}... [ > sig.log 2>&1 ]\n", argv[0]);

setbuf(stdout, NULL); /* Make stdout unbuffered */

parentPid = getpid();

printf("PID of parent process is: %ld\n", (long) parentPid);

printf("Foreground process group ID is: %ld\n",

(long) tcgetpgrp(STDIN_FILENO));

w for (j = 1; j < argc; j++) { / Create child processes /
childPid = fork();
if (childPid == -1)
errExit("fork");

if (childPid == 0) { / If child... /
e if (argv[j][0] == 'd') / 'd' --> to different pgrp /
if (setpgid(0, 0) == -1)
errExit("setpgid");

sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = handler;
r if (sigaction(SIGHUP, &sa, NULL) == -1)
errExit("sigaction");
break; / Child exits loop /
}
}

/* All processes fall through to here */

t alarm(60); / Ensure each process eventually terminates /

y printf("PID=%ld PGID=%ld\n", (long) getpid(), (long) getpgrp());
for (;;)
u pause(); / Wait for signals /
}
–––––––––––––––––––––––––––––––––––––––––––––––––––––– pgsjc/disc_SIGHUP.c
Suppose that we run the program in Listing 34-4 in a terminal window with the fol-
lowing command:

$ exec ./disc_SIGHUP d s s > sig.log 2>&1

The exec command is a shell built-in command that causes the shell to do an exec(),

replacing itself with the named program. Since the shell was the controlling pro-

cess for the terminal, our program is now the controlling process and will receive