I am trying to understand how can I make my program a daemon.So some things which I came across are In general, a program performs the following steps to become a daemon:
fork( )
. In the parent, call exit( )
. This ensures that the original parent (the daemon's
grandparent) is satisfied that its child terminated, that the daemon's parent is no
longer running, and that the daemon is not a process group leader. This last point
is a requirement for the successful completion of the next step.
Call setsid( )
, giving the daemon a new process group and session, both of
which have it as leader. This also ensures that the process has no associated
controlling terminal (as the process just created a new session, and will not assign
one).
Change the working directory to the root directory via chdir( )
. This is done
because the inherited working directory can be anywhere on the filesystem.
Daemons tend to run for the duration of the system's uptime, and you don't want
to keep some random directory open, and thus prevent an administrator from
unmounting the filesystem containing that directory.
Close all file descriptors.
/dev/null
.#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/fs.h>
int main (void)
{
pid_t pid;
int i;
/* create new process */
pid = fork ( );
if (pid == -1)
return -1;
else if (pid != 0)
exit (EXIT_SUCCESS);
/* create new session and process group */
if (setsid ( ) == -1)
return -1;
/* set the working directory to the root directory */
if (chdir ("/") == -1)
return -1;
/* close all open files--NR_OPEN is overkill, but works */
for (i = 0; i < NR_OPEN; i++)
close (i);
/* redirect fd's 0,1,2 to /dev/null */
open ("/dev/null", O_RDWR);
/* stdin */
dup (0);
/* stdout */
dup (0);
/* stderror */
/* do its daemon thing... */
return 0;
}
Can some one give me a link to existing source code of some program like Apache so that I can understand this process in more depth.