Linux features-Implement one-time tasks

First, the definition

At command: A timed task that specifies a time to perform a task that can only be performed once.

Second, the option

Iii. examples

1. Use the student user, create a task, execute after 2 minutes, append a row in/home/student/at.txt (created if not present), the content is the date command output result

[Email protected] ~]$ at now +2minutes
At> echo $ (date) >>/home/student/at.txt
At> <EOT>
Job at Thu Nov 3 11:20:00 2016

2. Check the student user's task list with ATQ to see the tasks in the previous step

[Email protected] ~]$ ATQ
10Thu 3 11:20:00 A student

3. Delete the task created in the previous step and view

Ten~

4. Switch to the root user, create a one-time task for the root user, print "$USER $ (date)" Output appended to the/home/student/at.txt file

Then go back to the student user, use ATQ to check the task, he is unable to see root (Other user's) task

 [[email protected] ~]# at now +2minutesat  > Echo $USER $ (date) > >/home/student/at.txtat  > <eot>job  11  at Thu Nov 3  11 : 23 : 00  2016  [ro[email protected]  ~]# su- student last Login:thu Nov  3  10
    :29 : 07  CST 2016  on Pts/0  [[email protected]  ~]$ atq[[email  Protected]  ~]$ 

5. Student also creates a task that executes after 2 minutes, performs the same actions as step 4, and now 2 users (root and student) have tasks waiting to be executed

[[email protected] ~]$ at now +2minutesat> Echo $USER $ (date) >>/home/student/at.txtat> &L T eot> at Thu  3: £ º

6. Perform the Atq check task with root user, the root user can see all the user's tasks

[Email protected] ~]# ATQ  One    Thu Nov  3: a rootof Thu-    Nov  3: Astudent

7. Back to the student user, the user can only view their own tasks

[Email protected] ~]$ ATQ  a    Thu Nov  3: Astudent

8 Switch to the root user, delete the 2 tasks created earlier, make sure the at list is empty

*

9. Using the student user, create a task to execute the reboot command on December 31, 10 o'clock in the morning this year

 to  . at > rebootat> <EOT>:00   .

10. Use student user, create a task, execute after 10 hours, restart sshd service

[Email protected] ~]$ at now +10hoursat> systemctl restart Sshdat> <EOT>16< /c3> at Thu  3: £ º

11. Use student user, create a task, 3 days after the 10 o'clock in the afternoon execution, restart the RSYSLOGD service

[Email protected] ~]$ at 10pm +3daysat> systemctl restart rsyslogd.serviceat> <EOT> /c2> at Sun Nov  6:xx:

12. Use student user, create a task, December 31, 2016 (denoted by mmddccyy) 23:59 points, execute poweroff command

:12312016at > poweroffat> <EOT>  to at::

13. Check the execution script of the last task and see the last shell command

[Email protected] ~]$ at-c -#!/bin/sh# atrun uid= +Gid= +# Mail Root0umask2Xdg_vtnr=1; export xdg_vtnrxdg_session_id=1; export Xdg_session_idhostname=desktop1.example.com; export Hostnameshell=/bin/bash; export shellhistsize= +; export Histsizeuser=student; export Userls_colors=rs=0:d i= -\;5\; -: ln= -\;5\;Wuyi: mh= -\; -\;5\; the:p i= +\; -\;5\; One: so= -\;5\; -: Do= -\;5\;5: bd= -\;5\;232\; -\;5\; One: cd= -\;5\;2
...
8\;5\; $: \*.oga= -\;5\; $: \*.spx= -\;5\; $: \*.xspf= -\;5\; $:; Export Ls_colorsmail=/var/spool/mail/student; export Mailpath=/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/student/.local/bin:/home/student/bin; export Pathpwd=/home/student; export Pwdlang=en_us. utf-8; export Langhistcontrol=ignoredups; export HISTCONTROLSHLVL=1; export Shlvlxdg_seat=seat0; export Xdg_seathome=/home/student; export Homelogname=student; export Lognamelessopen=\|\|/usr/bin/lesspipe.sh\%s; export LESSOPENCD/home/student | |{echo'Execution Directory Inaccessible'>&2Exit1}${shell:-/BIN/SH} <<'marcindelimiter5d48d7d0'poweroffmarcindelimiter5d48d7d0

14. Check the/var/spool/at directory to see the above script

[email protected] ~]# LL/var/spool/at/ Total --RWX------.1Student Student2972Nov3  One: +a0000f01792f38-RWX------.1Student Student2988Nov3  One: AA000100177ebb5-RWX------.1Student Student theNov3  One: thea000110177fca8-RWX------.1Student Student2974Nov3  One: $a000120179327fdrwx------.2Daemon Daemon6Nov3  One: -Spool[[email protected]~]#

15. Create a Y-queue task with a time of 3 minutes (indicated by the exact time as 11:55), append the y character to the/home/student/at.txt file

All:at > Echo Y >>/home/student/at.txtat> <EOT>   at Thu Nov  3: 

16. Create an X queue task, the time is exactly the same as the previous task, append x characters to the/home/student/at.txt file, simulate 2 tasks at the same time to execute

All:at > Echo X >>/home/student/at.txtat> <EOT>   at Thu Nov  3: 

17. Check 2 tasks with ATQ, confirm that the time is the same, the queue is Y and X

[[Email protected] ~]# ATQ theSat Dec to Ten:xx:xx  .a student -Thu Nov3  +: A:xx  .a student -Sun Nov6  A:xx:xx  .a student -Sat Dec to  at: -:xx  .a student +Thu Nov3  One: -:xx  .y root -Thu Nov3  One: -:xx  .X root

18. Wait for the X and Y queue to execute after 2 tasks (after their execution time), check the/home/student/at.txt file with the tail command, see X on top,

Y below, which shows the X queue executed first executes the Y queue (there are 2 tasks at the same time, the letter of the queue is preceded by the first execution)

[Email protected] ~]# tail/home/student/3: £ º

19. With root user, edit/etc/at.deny so that student users do not have permission to create one-time tasks

" Student " >>/etc/~]# Su- student last Login:thu Nov  3: c9>00 on pts/0~]$ @ now + do

20. With root user, create and Boundary/etc/at.allow, grant student user permission to create one-time tasks,

Now student can be used at command, because At.allow takes precedence over At.deny

[Email protected] ~]# Echo"Student">>/etc/At.allow[[email protected]~]# Su-student last Login:thu Nov3  A: -: -Cst .On pts/0[[Email protected]~]$ at now +3hoursat> <EOT>Job AAt Thu Nov3  the: the:xx  .[[Email protected]~]$

Linux features-Implement one-time tasks