Linux – Running a cron job every 5 minute on arch

arch linuxcronlinux

I've searched through some answers but nothing seems to clarify my confusion.

I have a cron job I want to run every 5 minutes:

*/5 * * * * cd /mnt/internal-storage/coindata && shell/command coins update

Do I place this in the /etc/cron.daily folder or create a /etc/cron.minutely?

Also what kind of file I create inside this folder?

Best Answer

The best solution for this is likely to add a line to your crontab. Accessing the crontab file may differ between implementations of cron, so I've provided commands for the two cron implementations in the official Arch repos. If you want a solution that does not require a specific cron implementation, I've written another answer that uses systemd/Timers instead.

crontab -e or variants of it use the EDITOR environment variable (defaults to vi). If you wish to use a different editor, export it to the EDITOR variable like so:

export EDITOR=vim

where vim is replaced with the editor of your choice.

Editing crontab with cronie:

crontab -e

Editing crontab with fcron:

fcrontab -e

Add your cron command to the file and save it:

*/5 * * * * cd /mnt/internal-storage/coindata && shell/command coins update

The format for lines in this file is

minute hour day_of_month month day_of_week command

If cron is not running, start its daemon.

For cronie: systemctl start cronie.service

For fcron: systemctl start fcron.service

If you want the commands in the crontab to continue to run after rebooting, make sure that the cron daemon is enabled:

systemctl enable cronie.service or systemctl enable fcron.service

Related Solutions

Cron – Running Job Every 15 Seconds

You can't go below one minute granularity with cron. What you can do is, every minute, run a script that runs your job, waits 15 seconds and repeats. The following crontab line will start some_job every 15 seconds.

* * * * * for i in 0 1 2; do some_job & sleep 15; done; some_job

This script assumes that the job will never take more than 15 seconds. The following slightly more complex script takes care of not running the next instance if one took too long to run. It relies on date supporting the %s format (e.g. GNU or Busybox, so you'll be ok on Linux). If you put it directly in a crontab, note that % characters must be written as \% in a crontab line.

end=$(($(date +%s) + 45))
while true; do
  some_job &
  [ $(date +%s) -ge $end ] && break
  sleep 15
  wait
done
[ $(date +%s) -ge $(($end + 15)) ] || some_job

I will however note that if you need to run a job as often as every 15 seconds, cron is probably the wrong approach. Although unices are good with short-lived processes, the overhead of launching a program every 15 seconds might be non-negligible (depending on how demanding the program is). Can't you run your application all the time and have it execute its task every 15 seconds?

Shell – Cron job for every minute executing out of order

There is no guarantee that cron will run tasks in the order in which they appear in the cronfile. In fact, it may well run two tasks simultaneously. So it's definitely not a good idea to have the tasks depend on each other. For example, in your cronfile, one task creates a file and another one (or three) appends to it. If the appender starts first, the creator will effectively delete the appender's work.

Better would be to create a driver script with the four every-minute runs of myscript and another one with the two every-five-minute runs. Then you can cron the two driver scripts, resulting in only one cron task for each time interval.

Best Answer

Related Solutions

Cron – Running Job Every 15 Seconds

Shell – Cron job for every minute executing out of order

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