Implementation of a time-based job scheduler based on Cron. It allows to schedule programs in a given time.

• UNIX-based operating system with support for POSIX.

To start cron daemon, run program with -s argument. It will create a new process which logs it's actions to cron_log.txt. To display all available options, use -h argument.

Following example will call a program from $PATH once on a fixed date with an argument done.

./cron -p 23/07/2021 14:32:11 spd-say done

This call will execute local program every 30 seconds with an argument arg.

./cron -p 30 -r /media/USB/sample-program arg

Last example will execute a program every day if system date predeceases given date by a day.

./cron -p 02/07/2021 00:00:00 -r ls -la

In order to cancel previously scheduled task, it's necessary to get it's ID by calling:

./cron -g
ID: 0 | Command: spd-say | Args: good  | Time 3.0 | Type: Runs periodically
ID: 1 | Command: ls | Args: la  | Time 350.0 | Type: Runs once
ID: 2 | Command: reboot | Args:  | Time 36000 | Type: Runs periodically

To cancel a task of choice:

./cron -c 2

Deamon process is detached from stdout, stdin and stderr. Scheduled tasks should not depend on those file descriptors.

Working directory of scheduled tasks is not changed. Therefore, all files created by tasks are stored in the same directory as cron binary.

It's important to stop cron deamon by calling it with -q paramenter. Otherwise, cron might hang the system upon reboot.

Command to build cron:

gcc cron.c main.c -o cron -lpthread -lrt