at跟crontab一樣，都是執行定時計劃任務的命令。但不同的是，crontab執行的循環的任務，而at執行的是一次性任務，任務執行完以后便失效。

設置任務：

at now + 1 week -f a.sh? ? ? #a.sh必須已存在

at 01:35 < my-at-jobs.txt

at < my.txt 01:35? ? ? ? ? ? #也可以把時間寫在后面

at now +2 minutes <<< "mkdir 123"

at now +10 minutes <

rm -rf 123

echo successful done > /var/log/messages

ENDMARKER

查看所有任務：

at -l

atq

查看單個任務：

at -c ID

刪除任務：

atrm 23

at -r 1

關于時間，可參考的語法：

noon? ? ? ? ? ? 12:00 PM October 18 2018

midnight? ? 12:00 AM October 19 2018

teatime? ? ? ? ? ? 4:00 PM October 18 2018

tomorrow? ? 10:00 AM October 19 2018

noon tomorrow? ? 12:00 PM October 19 2018

next week? ? 10:00 AM October 25 2018

next monday? ? 10:00 AM October 24 2018

fri? ? ? ? ? ? 10:00 AM October 21 2018

NOV? ? ? ? ? ? 10:00 AM November 18 2018

9:00 AM? ? ? ? ? ? 9:00 AM October 19 2018

2:30 PM? ? ? ? ? ? 2:30 PM October 18 2018

1430? ? ? ? ? ? 2:30 PM October 18 2018

2:30 PM tomorrow? ? 2:30 PM October 19 2018

2:30 PM next month? ? 2:30 PM November 18 2018

2:30 PM Fri? ? ? ? ? ? 2:30 PM October 21 2018

2:30 PM 10/21? ? ? ? ? ? 2:30 PM October 21 2018

2:30 PM Oct 21? ? ? ? ? ? 2:30 PM October 21 2018

2:30 PM 10/21/2018? ? 2:30 PM October 21 2018

2:30 PM 21.10.14? ? 2:30 PM October 21 2018

now + 30 minutes? ? 10:30 AM October 18 2018

now + 1 hour? ? 11:00 AM October 18 2018

now + 2 days? ? 10:00 AM October 20 2018

4 PM + 2 days? ? 4:00 PM October 20 2018

now + 3 weeks? ? 10:00 AM November 8 2018

now + 4 months? ? 10:00 AM February 18 2015

now + 5 years? ? 10:00 AM October 18 2019