shell-crontab（定時調度）

crontab: usage error: unrecognized option
usage:	crontab [-u user] file
	crontab [ -u user ] [ -i ] { -e | -l | -r }
		(default operation is replace, per 1003.2)
	-e	(edit user's crontab)
	-l	(list user's crontab)
	-r	(delete user's crontab)
	-i	(prompt before deleting user's crontab)

crontab -l
crontab -e
crontab file
crontab -r
#00 06 * * * shutdown -r now