Linux Task Plan detailed

Linux Task Scheduler, recurring task execution

One task at a time in the future: At,batch periodically runs a task: crontab execution Result: It will be sent to the user via email.

Mail easy to use

Check to see if your local email service is turned on         ~]$ netstat -tnlp     ~]$ ss -tnl     Make sure  127.0.0.1:25  is in the listening state. Local e-mail service:     smtp:simple mail transmission proticol    pop3:post office  procotol    imap4:internet mail access procotolmail Command:     mailx - send and receive Internet mail         mua:mail user agent Mail User agent: The user to send and receive mail the tool program     mailx [-s  ' Subject '] username[@hostname generation of]     message body:          (1) interactive input;. A single row can represent the end of the body, ctrl+d submissions can also be         ~]# mail -s   ' Hello ci '               ci         hi        .         EOT        [[email protected] ~]#           (2) via input redirection;          mail ci < /etc/fstab         (3) through the pipe;             cat /etc/fstab |mail -s  ' Fstab  file '  ci

AT command

AT&NBSP;[OPTION]...&NBSP;TIME&NBSP;&NBSP;&NBSP;&NBSP;TIME:&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;HH: Mm[yyyy-mm-dd]        noon (12 O'Clock Noon), Midnight (12 O'Clock Midnight), teatime (four o'clock in the afternoon), tomorrow        now+#             UNIT:minutes,hours,days,OR weeks                 [[email protected] ~]$ at now+2min                 at> cat  /etc/fstab                 at> <EOT>                 job 2 at 2016-08-16 10:16                 [[email protected] ~]$ at -l                 2       2016-08-16  10:16 a ci                 [[email protected] ~]$      at's job has a queue, denoted by a single letter, by default using the A queue common option:     -l:at -l =atq  View the queue of pending executions that were previously submitted, execution complete disappears   at -f  At.tasks now+5min  -f /path/from/somefile: Reads the job task from the specified file without having to enter it interactively; a command for a line of content in a file    at -d 3  Delete a job with the specified job number     at -d 3 = atrm 3   at -c : View specific contents of a specified job   -q queue: Indicate queue note: Job execution results are sent to the user who submitted the job by mail

Batch command:

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

Recurring Task Scheduler Cron

Cron Introduction

Service Program:     cronle Package: Main package, provides Crond daemon and related auxiliary tools, make sure Crond daemon (daemon) is running      centos 7:        systemctl status crond.service         active:active (running)                  CentOS 6:         service crond status              ...is running Note: Submitting a job to Crond is different from at, it requires a dedicated configuration file with a fixed format, and it is not recommended to edit the file directly using a text editor. To use the crontab command, Crontab prompts for syntax errors, and cron tasks fall into two categories      system cron tasks: As long as they are used to implement the system's own maintenance;           Manual editing:/etc/crontab file            This kind of task basically does not use the user self-modification      user cron Task:         command: crontab command Configuration format for      system crontab &NBsp;                    # example of job definition:        # &NBSP:---------------- minute  (0 - 59)         #  | &NBSP:------------- hour  (0 - 23)          # |  | &NBSP:---------- 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, a total of 7 fields;                   *  *  *  *  *: Define recurring time                     User-name: User identity for running tasks                    command to be executed: Quests               (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 specified user      user cron configuration format:/var/spool/cron/username         shell=/bin/bash        path=/sbin:/bin:/usr/ sbin:/usr/bin        mailto=root         HOME=/                 # For details see man 4 crontabs                 # Example of job definition:         #&NBSP:---------------- minute  (0 - 59)          # | &nbsp------------- hour  (0 - 23)         # |  | &nbsp.---------- day of  month  (1 - 31)         # |  |  |  .--- ---- 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 cron task, a total of 6 fields          (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) mail is sent to the current user

time notation:

(1) A specific value:     a value in the range of valid values for a given point in time;         Note: day or  week  and  day of month  are not used at the same time; (2) *     all values in the range of valid values at a given point in time; table "per" (3) A discrete value at a specified point in time:     multiple values separated by commas at a given point in time;     #,#,# (4) successive values:-      use at point-link start and End     #-# (5) at a specified point in time, define the step size:/#: #即步长     */2      Note:         (1) when the specified point in time cannot be divisible by stride length, its meaning will no longer exist;          (2) The minimum time unit is "minutes", want to complete the second level of program tasks, need to use additional mechanisms               is defined as a per-minute task: The loop executes multiple times per minute with the script implementation; Example: (1) 3 * * * *  : Hourly, 3 minutes per hour (2) 3 4 * * 5: Executed once a week, every Friday 4:3; (3) 5 6 7 * *  : 7th per month 6:5 (4) 7 8 9 10 *: Every year, October 9 8:7; (5) 9 8 * *  3, 7:8:9 (6) 0 8,20 *  per Wednesday and Sunday* 3,7:8 points and 20 points per Wednesday and Sunday (7) 0 9-18 * * 1-5 : Working hours Monday to Friday from 9 to 18, once per hour (8) */5 *  * * * : Perform a task once every 5 minutes (9) 77

Usage of the crontab command

crontab [-u user] [-l |-r |-e] [-i] [-s]-e: Edit task;-L: List All Tasks-r: Remove all Tasks; Delete/var/spool/cron/username file-I: Using the-R option to remove all tasks, remind the user to confirm-u user:root user can manage cron tasks for specified users note: The results of the operation are notified to the current user by mail, if the mail is rejected; (1) command >/dev/null (2) Command & amp;>/dev/null Note: When you define a command, you need to escape it if it needs to use%. But the percent placed in single quotation marks is not escaped;

Thinking: A task at a specified time because the shutdown does not suffocate, the next opportunity will not be automatically executed?

No, if you expect a certain time due to failure to execute, the next time after the boot, whether or not the corresponding point should be executed once, you can use Anacron implementation;

Practice:

1. Back up the/etc directory every 12 hours to the/backup directory, save the file name in the format "ETC-YYYY-MM-DD-HH.TAR.XZ" 2.2,4,7 a weekly backup/var/log/secure file to/logs directory with the file format " Secure-yyyymmdd ' 3. Take out every two hours. The line information in the/proc/meminfo file that starts with S or M is appended to the/tmp/meminfo.txt;

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Detailed Linux task plan