Rpncron

Hey, what is Rpncron?

Rpncron is a background process that runs particular programs at particular times (This sentence was taken from the cron debian package description :D ).

So it's like cron?

It is meant to be used like cron (Vixie's cron), yes, but unlike cron :

• Rpncron uses Reverse Polnish Notation (RPN) expressions to know when programs should be executed.
• Rpncron allows more fine-tuning when running programs (Like having a maximum running program count, the ability to change the process group and shell, the ability to run program at specified seconds, etc.)
• Rpncron allows you to have a really accurate fine-tuning of when the programs should run. For example, because each month don't have an even number of days, you cannot run a program exactly each two days with cron.
• The source code is first written to be as readable as possible, and THEN to be fast, so that updates and improvements can be added easily. It was also made in the aim that any code should be easily reusable, and not only in the project itself.

What are the goals of this project?

Let's make an other list! Here are the main goals :

• Being able to run a task at a regular inverval, no matter what the interval value is (Like each 37 seconds, or each 19 days).
• Have an up-to-date, easily readable and reusable source code.
• Being able to set several parameters before running the program.
• Being able to run multiple commands when the timer is reached.
• Avoid taking CPU when it's not needed (Like the way it's done in mcron).
• Have (almost) no dependancies.

Here are the other goals, that I will reach if I can and if it's not too boring and if I don't change my mind meanwhile :

• Being extensible (For example, by loading shared libraries to extend the RPN functionnalities.
• Being as fast as possible, without messing up with item 2.

What are the pros and cons of rpncron and its alternatives?

An other list! Here are they, to my mind, for the mere mortal every day user :

• cron (Vixie cron) :

  Pros: Really simple syntax, easy to understand and to run.

  Cons: No active development, no out of the ordinary feature, may contain bugs (according to a forum).

• rpncron :

  Pros: Flexible for the time computation part and the program execution part, configurable, and under development.

  Cons: RPN syntax may be a bit scary for new-comers, and the configuration files are quite verbose (for the moment).

• GNU cron (mcron) :

  Pros: It seems to be the most powerful alternative to cron for the time computation part. Small and easily reviewable source code.

  Cons: Requires the user to know scheme and to install a scheme interpreter.

• dillon's cron (dcron) :

  Pros: Complete rework of cron that adds some nice features.

  Cons: Not well known, and it seems to have the same limitations as cron for the time computation part. Also, no active development.

• cronie :

  Pros: Complete rework of cron that adds some features and also improves the security a lot.

  Cons: Not in the debian repositories (:-°), and same thing for the time computation part.

• gcron :

  Pros: ?

  Cons: Program not finished.

There is also Launchd, which, according to wikipedia, can replace cron. However, this program do much more than the others above, and may not work everywhere.

How do I install it?

No more list here, sorry! :-D. To install rpncron, just run these commands :

$ make rebuild
# make install

If you want to install it somewhere else (the default should be something like /usr/local), use :

$ mkdir -p build
$ cd build
$ cmake ..
$ cd ..
$ make
# make install

Can you show me some configuration samples? Is there a documentation for it?

Sure, sir! See the examples directory. You can also try to run files in this directory. The only thing they will do is creating/updating files in /tmp/ and printing things on stdout/stderr. Also, if anything is printed or if the return code is not OK, they may be written into your syslog log file and/or sent by mail to yourself.

You can read details about the configuration files syntax in the doc/rpncron-config.md file. You can also read how to use the rpncron and rpncrontab commands in doc/rpncron.md and doc/rpncrontab.md.

How is the development going?

Here is a list (YEAH!) of what is missing and what is done :

• Run the programs when needed.
• Add the option to run the program as a whole script instead of a set of commands.
• Change the setuid/setgid/cwd of the ran programs if needed.
• Write the make install code.
• Search for security issues.
• Prepare some unit tests.
• Test extensively the program.
• Check for portability issues (mainly in src/os).
• Change the spawned process environment.
• Handle errors in an other way than printf().
• Log informations.
• Send mails on error.
• Use the given verbosity level.
• Give a way to write the PID somewhere.
• Simultaneous processes limit.
• Write configuration files documentation.
• Check for file updates in an other thread and combine the process of waiting for updates and sleep() in the main run loop, using select().
• And many more features, that I will pick from other projects... ;-)