crond

Both crontab and rc.local has been more or less removed or disabled on many distro's. Systemd is replacing most of the old features, and that is fine. It's a hell of a lot better than older init systems, crontab etc. (it is, deal with it), but it's also more complex if you just want to quickly add a script during boot or to run each hour or each day. These are basic things that should be much quicker to add, which is what this small install script provides.

It creates a cron/startup script that will run custom scripts (/etc/rc.cron.d/) depending on different timers that is provided by the filename itself. It is fast and simple to add and remove scripts and it covers most basic needs.

Adding a script

Simply create a script /etc/rc.cron.d/[email protected] and fill it with your required code. There are many timers to use:

Timer	Description
@startup	Run when the system boots
@shutdown	Run when the system shuts down
@network	Run when the network has been brought up
@hourly	Run ones every hour
@quarter-hourly	Run ones every 15 minutes
@daily	Run ones every day
@weekly	Run ones every week
@biweekly	Run ones every two weeks
@montly	Run ones every month
@quarterly	Run every 3 months
@semiannually	Run every 6 months
@annually	Run ones every year
@weekday	Run only every weekday, monday through friday
@weekend	Run only on weekends, saturday and sunday
@any	Run on all timers

The @any timer will match any timer that is run. The timer that was initiated can be fetched via the first argument $1 within a script.

You can also have it run on a specific day each week

Timer	Description
@mondays	Run every monday
@tuesdays	Run every tuesday
@wednesdays	Run every wednesday
@thursdays	Run every thursday
@fridays	Run every friday
@saturdays	Run every saturday
@sundays	Run every sunday

Timer-less filenames

If a file does not provide @timer in it's filename, it will be the same as @any. So [email protected] is the same as simply myscript.sh.

Detached scripts

You can run a script in detached mode (background without being coupled/depended on the main process). To do this, simply use the .shd file extension instead of .sh

File Extension	Description
[email protected]	This will run in the main process. The main process will wait for this script to finish.
[email protected]	This will run in it's own detached process. The main process will continue to the next script.

Note that in detached mode, output from the scripts process is not gonna be redirected to the log file

Installation

Just download and run the script from a terminal

wget https://raw.githubusercontent.com/dk-zero-cool/crond/main/crond_install.sh
chmod +x crond_install.sh
./crond_install.sh

Further help Linus' of the world? https://www.cyberciti.biz/faq/how-to-execute-a-shell-script-in-linux/

Multiple Timers

Even though you can run all timers against one script by naming it @any or leaving out any timer in the name, a better way is using links, unless you absolutly must run it against ALL timers. Even if you filter out the timers you don't need within the script, the script is still executed which does produce a litle overheat, especially if it is executed as a detached process. Instead leave out the extenstion .sh and .shd and create links for the required timers.

# ls -l /etc/rc.cron.d/
-rwxr-xr-x 1 root root  000 xxx 0 0:00 myscript
lrwxrwxrwx 1 root root    0 xxx 0 0:00 [email protected] -> myscript
lrwxrwxrwx 1 root root    0 xxx 0 0:00 [email protected] -> myscript
lrwxrwxrwx 1 root root    0 xxx 0 0:00 [email protected] -> myscript
lrwxrwxrwx 1 root root    0 xxx 0 0:00 [email protected] -> myscript

Logs

The main log can be found in journalctl within the identifier rc.cron

$ journalctl -t rc.cron

Each detached process will have their own log entries using identifiers rc.cron#<number> where <number> is the script inode. You can find reference to this within the main log:

$ journalctl -t rc.cron
<date> rc.cron: Starting script <file> (rc.cron#<inode>) in detached process

From here you can access the log entry from the detached script:

$ journalctl -t rc.cron#<inode>
...