How to execute additional commands during system startup using cron

Use cron service to execute additional commands as the specified user using cron during system startup.

Use @reboot time specification to execute the command once after the system reboot.

The root can use cron service to set noop IO scheduler for sda device at boot.

$ (sudo crontab -u root -l 2>/dev/null; echo -e "# io scheduler\n@reboot (/bin/echo noop | /usr/bin/tee /sys/block/sda/queue/scheduler)") | sudo crontab -u root -

$ sudo crontab -l

# use noop io scheduler for sda
@reboot (/bin/echo noop | /usr/bin/tee /sys/block/sda/queue/scheduler)

Users can use cron service to clear history at boot.

$ (crontab -u $(whoami) -l 2>/dev/null; echo -e "# clean history on reboot\n@reboot (: | /usr/bin/tee ~/.bash_history)") | crontab -u $(whoami) -

$ crontab -l

# clean history on reboot
@reboot (: | /usr/bin/tee ~/.bash_history)

There are many other possibilities, as you are not limited to these two simple usage scenarios.