The at command implements the function of delaying tasks.
at time
at now+5min
at 16:00
>touch /mnt/file{1..10}
>ctrl+d
at -l to view the task number
at -c 3 finds task number 3
at -r 3 undo task number 3
Black and white list of at commands:
[root@node1 ~]# useradd westos Create two users for easy experimentation
[root@node1 ~]# useradd linux
[root@node1 ~]# at now+1min Super user can execute at command
at> <EOT>
job 1 at Sat Apr 14 16:50:00 2018
[root@node1 ~]# su - westos
[westos@node1 ~]$ at now+1min switch to the westos user to execute the at command, you can use the at command
at> <EOT>
job 2 at Sat Apr 14 16:50:00 2018
[westos@node1 ~]$ logout
[root@node1 ~]# su - linux Switch to the linux user to execute the at command, you can use the at command
[linux@node1 ~]$ at now+1min
at> <EOT>
job 3 at Sat Apr 14 16:51:00 2018
[linux@node1 ~]$ logoutvim
[root@node1 ~]# vim /etc/at.deny add linux to the blacklist
[root@node1 ~]# at now+1min
at> <EOT>
job 4 at Sat Apr 14 16:52:00 2018
[root@node1 ~]# su - linux
Last login: Sat Apr 14 16:49:56 CST 2018 on pts/0
[linux@node1 ~]$ at now+1min Linux cannot execute at command
You do not have permission to use at.
[linux@node1 ~]$ logout
[root@node1 ~]# su - westos
Last login: Sat Apr 14 16:49:31 CST 2018 on pts/0
[westos@node1 ~]$ at now+1min
at> <EOT>
job 5 at Sat Apr 14 16:52:00 2018
[westos@node1 ~]$ logout
[root@node1 ~]# vim /etc/at.deny 将黑名单用户删除掉
[root@node1 ~]# ll /etc/at.allow 添加linux为白名单
ls: cannot access /etc/at.allow: No such file or directory
[root@node1 ~]# vim /etc/at.allow
[root@node1 ~]# at now+1min
at> <EOT>
job 6 at Sat Apr 14 16:53:00 2018
[root@node1 ~]# su - westos
Last login: Sat Apr 14 16:51:34 CST 2018 on pts/0
[westos@node1 ~]$ at now+1min westos不再白名单内不可以执行at命令
You do not have permission to use at.
[westos@node1 ~]$ logout
[root@node1 ~]# su - linux
Last login: Sat Apr 14 16:51:25 CST 2018 on pts/0
[linux@node1 ~]$ at now+1min
at> <EOT>
job 7 at Sat Apr 14 16:53:00 2018
[linux@node1 ~]$ logout
[root@node1 ~]# vim /etc/at.allow 将白名单用户删除掉
***白名单出现时黑名单失效，所有人不可以登录，只有root用户以及白名单里面的用户可以执行at命令。