a、crontab -e，添加如下内容：

*/1 * * * * sh && echo "dd" >> /logs/cron-cc.log
*/1 * * * * sleep 30 && echo "cc" >> /logs/cron-cc.log

b、重启crond

systemctl reload crond
systemctl restart crond

service crond reload

c、查看当前用户定时任务

crontab -l

d、通过日志查看是否生效

tail -f /logs/cron-cc.log