I wouldn't recommend you to choose 2., because you would be, in fact, repeating cron functionality. Yes, it will require a simple event loop (where your events are timer triggering, possibly, provided by sleep function). Use some kind of python approach (a library, for example) for your script to be able to daemonize itself. There is a variety of different cron daemons, but your GNU/Linux system should have it already installed. You add your script into a crontab or place a symlink to it into a special directory and the daemon handles the job of launching it in the background. Cron is a common name for a GNU/Linux daemon that periodically launches scripts according to a schedule you set. In the next step, change the working directory to the root directory according to the value of the argument you passed.Make a proper cron job that calls your script. Notice that the PID, PGID, and SID values of your process are the same. The ? sign in the TT field indicates that your process is no longer connected to a terminal. The new status of your process is as follows: ps -C test -o "pid ppid pgid sid tty stat command" test.cĪfter compiling and running the application again, go to the terminal where you made your reviews.
Now that you've inspected the state before _daemon called, you can now remove the first getchar function in the test.c code.
DAEMON TOOLS LINUXRA CODE
The piece of code to add is as follows: if (setsid() = -1) It is mentioned above that for the next step, a new session should open and the process should be disconnected from the control terminal. You can now see that the parent process of your process is the systemd process. Now examine who is the parent process of the process using the following command: ps -jp 1 Ps -C test -o "pid ppid pgid sid tty stat command"įirst of all, you can say that the new subprocess is running in the background since you do not see the + character in the STAT field. When you look at the STAT field, you see that your process is running but waiting for an off-schedule event to occur which will cause it to run in the foreground. ps -C test -o "pid ppid pgid sid tty stat command" In this case, the _daemon function has not been called yet. Here, you'll have to use the ps command to get process-related information. You can see that the values related to your process are as follows. Run the application and switch to a different terminal without pressing any other keys. Now compile the application with the following command and examine the status of the process before and after _deamon is called: gcc -o test test. In this case, your new process will be a subprocess of init and will continue to run in the background. In the code above, _daemon creates a child process and then kills the parent process. To create a daemon, you need a background process whose parent process is init. Pid = fork() // Fork off the parent process
For this purpose, a sub-process is forked from the init process first, and then the upper process is terminated with exit.
A background running process is created with init as its parent process.This way, the system can report the received errors to the user and the process will be terminated with an appropriate error code. Initial operations, such as reading configuration files or obtaining necessary system resources, must be performed before the process becomes a daemon.nfsd: Allows file sharing over the networkĪlso, daemon processes are usually named to end with the letter d, although it's not mandatory.įor a process to run as a daemon, the following path is followed:.sshd: Allows login to the system from remote machines.crond: Makes commands run at the specified time.A Brief Introduction to How Daemons Are CreatedĪ lot of daemons run on the system and some familiar daemon examples are as follows:
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