How to use the Task Scheduler command at and Crontab on Linux systems

Source: Internet
Author: User

First, summarize the task plan on Linux system at, crontab detailed use method

1. Planning Task Description

Perform a task at a time in the next point: At,batch;

Perform a task periodically: crontab;

2. e-Mail Service

Scheduled tasks send results to users who perform tasks by default in the form of a message

Mail command:

Mail username (@hostname): Enter the interactive send and receive mail interface

Mail-s ' SUBJECT ' [email protected]: Set message subject

</path/from/somefile: Send file content to recipients

echo "XXX" | Mail-s ' SUBJECT ' [email protected]: send echo output to Recipient

3. At command use

At [option] ..... Time

(1) Common options

- q queue:at Job Queue

-f/path/from/somefile: Reads the job to run from the specified file

-L: View the list of jobs that are running in the job queue (equals the ATQ command)

-C At_job_num: Look at the contents of the Run job

-D Number: Deletes the specified job, equivalent at RM

(2) Time format

Absolute time:

hh:mm,
Mmdd[cc]yy, Mm/dd/[cc]yy, dd.mm.[cc]yy or [cc]yy-mm-dd

Relative time:

now+ #UNIT (now+3minute)

Minute, hour, day, week

Blur Time:

midnight,noon,teatime

[Email protected] ~]#/etc/init.d/atd statusatd is stopped[[email protected] ~]#/etc/init.d/atd startstarting ATD: [OK]  [Email protected] ~]# at 17:19at> ls/etcat> cat/etc/fstabat> <eot>job 2 at 2015-09-08 17:19you with Mail In/var/spool/mail/root

4. Batch: The system chooses to run the specified task when the resource is idle.

5. Crontab: Recurring Task plan

Daemon: Crond

[Email protected] ~]#/etc/init.d/crond statuscrond (PID 1977) is running ...

(1) System cron Task: No user identity is run by default, so you need to specify additional runner

Configuration file:/etc/crontab

(2) User Cron Task: Submitted by a user, run as submitter by default (CRONTAB-E recommended)

Configuration file:/var/spool/cron/username

(3) Configuration file field parsing

[[email protected] ~]# cat /etc/crontabshell=/bin/ bashpath=/sbin:/bin:/usr/sbin:/usr/binmailto=roothome=/# for details see man 4  CRONTABS#&NBSP;EXAMPLE&NBSP;OF&NBSP;JOB&NBSP;DEFINITION:#&NBSP---------------- minute  (0 -  59) # |  .------------- hour  (0 - 23) # |  |   .---------- day of month  (1 - 31) # |  |  |  . ------- month  (1 - 12)  OR jan,feb,mar,apr ...# |  |  &NBSP;|&NBSP;&NBSP;|&NBSP;&NBSP---- day of week  (0 - 6)   (sunday=0 or &NBSP;7)  or sun,mon,tue,wed,thu,fri,sat# |  |  |  |  |#  *  *  *  *  * user-name command to be  Executed 

*****:5 Time Point: (A few hours and weeks)

Minutes: 0-59

Hours: 0-23

Day: 1-31

Weeks: 0-7

Months and weeks not recommended for simultaneous use

User-name: Run the task as a user

command to be executed: the task to run (command)

Instance:

Annual: 2 3 4 5 *

Monthly: 20 18 6 * *

Daily: 20 9 * * *

Weekly: 17 16 * * *

Per hour: 3 * * * *

Per minute: * * * * * *

Point-in-time notation:

1. *: Each time point within the valid value range of the time point

2.-: Indicates a specific continuous time range (3 * * 1-5 command)

3,,: denotes discrete point of time (2 * * 2,4,6 command)

4./#: one time unit per # in the effective time range; Used to specify the frequency ()

*/3 * * * * command: executed every 3 minutes

* */3 * * Command: Every three hours on arrival, every minute of this hour is executed

6 */3 * * Command: No three hours to execute

Note: It is not accurate to 7 minutes at a time (sleep mechanism can be used)

(4) crontab command

crontab [-u user] [-l] [-r] [-e]

-u User: Not managing your own cron task, but specifying the target user's cron task; Root has the right to manage other users ' cron tasks default to manage your own

-l:list, List tasks

-r:remove, remove All Tasks

-e:edi T, edit, open a default editor for the current shell session to edit the Cron task table

Note:   

(1) If you do not want to receive notification messages for task execution results:

COMMAND >/dev/null

COMMAND &>/dev/null

(2) for crontab file,% has a special function, if the command will appear in the%, remember to escape, or use single quotation marks to its reference;

(3) Crontab's path variable is not exactly the same as the user's variable, so it is recommended that the task in cron use an absolute path

/root/bin/a.sh (including commands to be used in the script)

Second, every Monday to Saturday 3:20 A.M., run the CP command to archive the/etc/directory, storage location is/backups/etc-yyyy-mm-dd;

[[email protected] ~]# mkdir-pv/backupsmkdir:created directory '/backups ' [[email protected] ~]# Crontab-eno crontab fo R root-using an empty ONE20 3 * * 1-6/bin/cp-a/etc/backups/etc-' Date +f% '

three, every Sunday 2:30 A.M., run the CP command to backup the/etc/fstab file, the storage location is/backup/fstab-yyyy-mm-dd-hh-mm- SS;

2 * * 7/bin/cp-a/etc/fstab/backup/fstab-' date +f '

12 o'clock every night, get all lines in the/proc/meminfo file that begin with S or M, append to the/statistics/meminfo.txt file, and precede the daily message with a similar =============== separator line

[[email protected] ~]# mkdir-pv/statisticsmkdir:created directory '/statistics ' 0 0 * * */bin/echo-e "===========\n" >>/statistics/meminfo.txt &&/bin/grep "^[s| M] "/proc/meminfo >>/statistics/meminfo.txt





How to use the Task Scheduler command at and Crontab on Linux systems

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