To the best of the authors knowledge, ocron is the only cron implementation available that does not need to wake up every single minute. Instead, ocron only either wakes up when it wants to execute a job, or if a user-configurable amount of time has elapsed (usually a whole hour), to make sure the system time wasn't changed much in the mean time. This way, ocron can reduce overall power consumption and CPU time spent.

Also, it looks like ocron uses less memory than other cron implementations - This might make a difference on very low-power (embedded) devices.

ocron understands all the usual syntax features and common extensions that you've come to expect from a cron daemon:

• Both comments and blank lines are allowed.
• Rules are of the following form:

  minutes   hours   month-days   months   week-days   command
  

• In the first 5 fields, '*' means that the field is unspecified, '-' can be used for inclusive ranges, and a '/' after a '*' or after a range specifies a period.
• For the months and week-days fields, 3-letter case-insensitive aliases may be used (for example: Jan, JUL, aug).
• In the week-days field, 0 and 7 both mean Sunday.
• Commands are executed if either the month-day or the week-day matches the current day.

ocron should handle both system clock changes and Daylight Savings Time gracefully.

If a rule contains syntax errors and cannot be parsed, it is simply ignored (with a warning message), so other rules will still execute just fine. Also, ocron will run correctly if no valid rules are specified or the crontab file doesn't exist.

After (re-) loading the crontab, ocron doesn't allocate any new memory, so memory leaks and out-of-memory situations can't arise.

A lot of effort has been made to keep ocron free of any signal-related race conditions.

You only need make and a C99 / POSIX.1.2008 compatible C compiler (like GCC). Simply change into this directory, run make, and then as superuser run make install. You can edit the files config.mk and config.h to adapt the build settings to your system. The Makefile honors both the PREFIX and DESTDIR environmental variables, used for packaging etc.

If you want to run ocron at startup like any other daemon, you will have to write a service for your init system (systemd / Sys V init / runit / ...). Note that ocron never daemonizes itself and always logs to the system log. If you need it to run in the background, consider using Linux' daemonize(1) or FreeBSD's daemon(1). Most init systems want to do the daemonization themselves.