Listing 1. Daemon Start-up Code
/*
* Listing 1:
* fork(), closing controlling terminal, changing
* session group, fork(), change current working
* directory, set umask
* Ivan Griffin (ivan.griffin@ul.ie)
*/
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv)
{
struct rlimit resourceLimit = { 0 };
int status = -1;
int fileDesc = -1;
/*
* somewhere in the code
*/
status = fork();
switch (status)
{
case -1:
perror(fork());
exit(1);
case 0: /* child process */
break;
default: /* parent process */
exit(0);
}
/*
* child process
*/
resourceLimit.rlim_max = 0;
status = getrlimit(RLIMIT_NOFILE,
&resourceLimit);
if (-1 == status) /* shouldn't happen */
{
perror(getrlimit());
exit(1);
}
if (0 == resourceLimit.rlim_max)
{
fprintf("Max number of open file
descriptors is 0!!\n");
exit(1);
}
for (i = 0; i < resourceLimit.rlim_max; i++)
{
(void) close(i);
}
status = setsid();
if (-1 == status)
{
perror(setsid());
exit(1);
}
status = fork();
switch (status)
{
case -1:
perror("fork()");
exit(1);
case 0: /* (second) child process */
break;
default: /* parent process */
exit(0);
}
/*
* now we are in a new session and process
* group than process that started the
* daemon. We also have no controlling
* terminal */
chdir("/");
umask(0);
fileDesc = open("/dev/null", O_RDWR);/* stdin */
(void) dup(fileDesc); /* stdout */
(void) dup(fileDesc); /* stderr */
/*
* the rest of the daemon code executes in
* this environment
*/
return 0;
}
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