freebsd中用cron来使机器在启动时，启动某一服务的方法

今晚看freebsd 的handbook，看到15.2.2时，看到可以用服务启动服务。
cron工具提供了一个独有的功能， 以@reboot来指定时间。
不是很明白，到网上google一下，看到一个老外哥们写的，cp过来以做备忘。
(Vixie cron is named after Paul Vixie, the creator of BIND and other Unix goodness.)
While looking at the manual page for the crontab file format, I discovered a chunk that I'd never seen before:
Instead of the first five fields, one of eight special strings may
appear:
string meaning
------ -------
@reboot Run once, at startup.
@yearly Run once a year, "0 0 1 1 *".
@annually (same as @yearly)
@monthly Run once a month, "0 0 1 * *".
@weekly Run once a week, "0 0 * * 0".
@daily Run once a day, "0 0 * * *".
@midnight (same as @daily)