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
crontab -e
and put it there?/etc/cron.d
directory. See man page crontab(5). Line format is:minute hour dom month user command...
. You might have an example in the directory.