Deamon process in linux

The deamon process in linux-general Linux technology-Linux programming and kernel information. The following is a detailed description. The key to designing a deamon process in linux is as follows:

1. fork twice.
2. fork becomes the process group Header between the first and second times.
3. Change the working directory.
4. Ignore the signal.
5. Set the read/write mask.

This is a routine collected from the network. It demonstrates the above points very well and stores this memo.

# Include
# Include
# Include
# Include

Void main (int argc, char ** argv)
{
Time_t now;
Int childpid, fd, fdtablesize;
Int error, in, out;

/* Ignore terminal I/O signals and STOP signals */
Signal (SIGTTOU, SIG_IGN );
Signal (SIGTTIN, SIG_IGN );
Signal (SIGTSTP, SIG_IGN );
Signal (SIGHUP, SIG_IGN );

/* The parent process exits and the program runs in the background */
If (fork ()! = 0)
{
Exit (1 );
}
If (setsid () <0)
{
Exit (1);/* Create a new meeting group */
}

/* The sub-process exits and the sun process loses its control terminal */
If (fork ()! = 0)
{
Exit (1 );
}
If (chdir ("/tmp") =-1)
{
Exit (1 );
}

/* Disable open file descriptors, including standard input, standard output, and standard error output */
Fd = 0;
For (fdtablesize = getdtablesize (); fd <fdtablesize; fd ++)
{
Close (fd );
}

Umask (0);/* reset the file creation mask */
Signal (SIGCHLD, SIG_IGN);/* ignore SIGCHLD signal */

/* Here, you can do the service routine code you want to do. Generally, it is an endless loop. If you want to exit with control, you can set the signal to be obtained. The following example shows a log writing routine.
*/

/* Write log, test result */
Syslog (LOG_USER | LOG_INFO, "daemon test! \ N ");

While (1)
{
Time (& now );
Syslog (LOG_USER | LOG_INFO, "Current Time: \ t % s \ t \ n", ctime (& now ));
Sleep (6 );
}
}

The above program is compiled in gcc4.0.1 and runs stably in the fc4-2.6.11.

Syslog will connect to the syslogd service and output messages in the/var/log/message file. Therefore, you need to start the syslogd service. Otherwise, it will not be displayed in the/var/log/message file.