Linux Task Scheduler, recurring task execution

Introduction

Perform a task at some point in the future: at, Batch
To run a task periodically: crontab
Execution result: will be sent to the user by mail
Check if the mailbox service is on: (25 port)
~]# NETSTAT-TNLP
~]# SS-TNL

Local Email service:

SMTP:SIMPLE&NBSP;MAIL&NBSP;TRANSMISSION&NBSP;PROTOCOL&NBSP;&NBSP: Simple Mail Transfer Protocol, e-mail;pop3:post office  Procotol: Post Office Protocol Imap4:internet mail access procotol: Internet Mail Access Protocol Mail command: &NBSP;&NBSP;&NBSP;&NBSP;MAILX  - send and receive Internet mail         MUA:Mail User Agent,  the user to send and receive mail the tool program; &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;MAILX   [-s  ' SUBJECT ']  username[@hostname]                      title             user              message body generation:                  (1)   Interactive input ;                  point number (.) A separate row may indicate the end of the body; Ctrl+d submit also;                       e-Mail                      [[email protected] ~]# mail -s  ' Hello hdfs '  hdfs                      How are you these days?                     .                     EOT                     [[email  protected] ~]#                     Receive email                      mail                     #        #输入数字查看对应第几封邮件                      q         #q退出                   (2)   via input redirect;                     mail -s  ' Hello hdfs '   Hdfs < file.txt (body content)                   (3)   through pipe;                     cat file.txt | mail -s  ' Hello hdfs '  hdfs 

At command: Perform a scheduled task, corresponding to the service ATD

at  [option]... time    time:         hh:mm [yyyy-mm-dd]        noon,midnight, teatime noon, at night, Tea time (four o'clock in the afternoon)         tomorrow tomorrow          now+#            unit:minutes, hours,  days, or weeks    at jobs have queues, denoted by a single letter, and by default use the A queue;     common options:         -l: View Job queue, equivalent to atq         -f /path/from/somefile: Reads the job task from the specified file without having to interactively enter the;             at -f file  now+5min        &NBSP;-D: Deletes the specified job, which is equivalent to atrm;        -c: View the specific contents of the specified job;         -q&nBsp Queue: Indicates queues;     note: Job execution results are sent by mail to the user submitting the job;         [[ email protected] ~]# at 10:31        at>  Echo qq > /root/test.log        at> echo  aa >> /root/test.log        at> <eot >        job 4 at 2017-08-25 10:31         [[email protected] ~]# at -l         4   2017-08-25 10:31 a root         [[email protected] ~]# ll          Total dosage  44        -rw-------.  1 root root   1223 5 Month &NBSP;&NBsp;18 15:10 anaconda-ks.cfg        -rw-r--r--.  1  Root root 25166 5 Month   18 15:10 install.log         -rw-r--r--.  1 root root  7992 5 Month   18 15:09  install.log.syslog        [[email protected] ~]#  At -l        4   2017-08-25 10:31 a  root        [[email protected] ~]# at -l         [[email protected] ~]# ll          Total dosage  48        -rw-------.  1  root root  1223 5 Month   18 15:10 anaconda-ks.cfg         -rw-r--r--.  1 root root 25166 5 Month   18 15:10 install.log         -rw-r--r--.  1 root root  7992 5 Month   18  15:09 install.log.syslog        -rw-r--r--  1  root root     6 8 Month   25 10:31 test.log         [[email protected] ~]# cat test.log         qq        aa         [[email protected] ~]#

Batch command:

Batch gives the system the option to perform the specified task at a time when the system resources are more idle;

Recurring Task Scheduler: Cron

Service Program:     cronie: Main package, provide Crond daemon and related auxiliary tools; ensure Crond daemon (daemon) is running:     CentOS 7:        systemctl  status   crond.service            active: active  (running)  ... ...    CentOS 6:         service  crond  status             ... is running. Submitting a job to Crond is different from at, it requires a dedicated configuration file with a fixed format, it is not recommended to edit the file directly using a text editor; To use the crontab command;     cron task is divided into two kinds of:         system cron task: Mainly used to realize the maintenance of the system itself;              Manual editing:/etc/crontab file           User Cron Task:              command: crontab command      system cron Configuration format:/etc/crontab        shell=/bin/bash         PATH=/sbin:/bin:/usr/sbin:/usr/bin         MAILTO=root        # For details see  man 4 crontabs        # example of job  DEFINITION:        #&NBSP---------------- minute  (0 -  59)         # |  ------------- hour  (0  - 23)         # |  |  .----------  day of month  (1 - 31)         # |   |  | &NBSP:------- month  (1 - 12)  or jan,feb,mar,apr  ...        # |  |  |  | &nbsp.---- day  of week  (0 - 6)   (sunday=0 or 7)  or sun,mon,tue,wed,thu,fri, sat        # |  |  |  |   |        # *  *  *  *  *  user-name  command to be executed          Note:             (1)   Each row defines a recurring task with a total of 7 fields;                 *  *   *  *  * :  Define recurring Time                  user-name :  user identities for running tasks                  command to be executed: Task Command               (2)   The environment variable here differs from the environment that is obtained after the user logs on, so it is recommended that the command use an absolute path, or a custom path environment variable;              (3)   Execution result message sent to mailto named user       user cron configuration format:/var/spool/cron/username        shell=/ bin/bash        path=/sbin:/bin:/usr/sbin:/usr/bin         MAILTO=root        # For  Details see man 4 crontabs        # example  of job definition:        # .----------------  minute  (0 - 59)         # |  .----- -------- hour  (0 - 23)         # |  |  .---------- day  of month  (1 - 31)         # |   |  | &NBSP:------- month  (1 - 12)  OR jan,feb,mar,apr  ...        # |  |  |  |   .---- day of week  (0 - 6)   (sunday=0 or 7)  or sun,mon, tue,wed,thu,fri,sat        # |  |  |   |  |        # *  *  *   *  *   command to be executed              Note:              (1)   Each row defines a cronServices, total 6 fields;             (2)   The environment variables here are different from the environment that the user has been logged into. Therefore, it is recommended that the command use an absolute path, or a custom PATH environment variable;             (3)   Message sent to current user;     time notation:         (1)   Specific value;              value in the range of valid values for a given point in time;                  Note: Day of week and Day of  month is not used in conjunction with the Sun and moon. Monday use;         (2)  *              all values in the range of valid values at a given point in time; table "per.."          (3)   Discrete value:,              use a comma-separated number of values at a point in time;                  #,#,#         (4)   Continuous value:-              Use at point-in-time-connect start and end                  #-#         (5)   Define step:     at a specified point in time          /#: #即步长; Example:*/#              Note:                  (1)   The specified point in time cannot be divisible by stride length, and its meaning will not exist;                  (2)   Minimum time unit is "minute", want to complete "second" level task, need to use additional mechanism;                      Defined as a per-minute task: Then use the script implementation to loop through the;     sample multiple times per minute:         (1)  3 * * * *:performed once per hour; 3rd minutes per hour;         (2)  3 4 * * 5: Once a week ; 5 of the Week 4:3;         (3)  5 6 7 * *: executed once a month ; 7th per month, 6:5;         (4)  7 8 9 10 *: Executed once a year ; every October 9 8:7;         (5)  9 8 * * 3,7: every Wednesday and Sunday;          (6)  0 8,20 * * 3,7:          (7)  0 9-18 * * 1-5:          (8)  */5 * * * *: Perform a task once every 5 minutes;          (9)  */7    crontab command:         crontab  [-u user] [-l | -r | -e] [-i]              -E: Editing tasks;             -l: List All Tasks;             -r: Remove all Tasks; Delete/var/spool/cron/username files;             -i: Prompt user to confirm;   when removing all tasks with the-r option           -u user:root users can manage cron tasks for specified users;                    crontab  -u USERNAME -e      Note: The result of the operation is notified to the current user by mail, if you refuse to receive mail:          (1)  COMMAND > /dev/null          (2)  COMMAND &> /dev/null     Note: When you define a command, if you need to use%, It needs to be escaped, but the percent placed in single quotes does not escape;    a     think: A task is not executed at the specified time due to shutdown, the next opportunity will not be automatically executed?          will not!.         if you expect a certain time to fail to execute, after the next boot, whether or not to the corresponding point in time to perform once, can use   Anacron Realization;     Homework: Anacron and its application;

Practice:

1, every 12 hours to backup the/etc directory to the/backups directory, save file name format "ETC-YYYY-MM-DD-HH.TAR.XZ" 2, weekly 2, 4, 7 backup/var/log/secure files to/logs directory, the file name format is " SECURE-YYYYMMDD "; 3. Remove the line information in the current system/proc/meminfo file starting with S or M in the/tmp/meminfo.txt file every two hours;

This article is from the "Caterpillar Small Smelly Smelly" blog, please make sure to keep this source http://moerjinrong.blog.51cto.com/11124564/1961859

Linux Task Scheduler, recurring task execution