Linux Scheduled Tasks

Note: The results of each execution of a Linux task plan, including errors, will be sent to the administrator in message format, so you must install the Mail service to view the results of the task execution

1. E-Mail Service:

Smtp:simple Mail Transmission protocol

/var/spool/mail/username

Pop3:post Office Protocol

Imap4:internet Mail Access Protocol

Mail command:

Mail: Enter the interactive email interface;

Mail-s ' SUBJECT ' [email protected]

Mail-s ' SUBJECT ' [email protected] </path/from/somefile

COMMAND | Mail-s ' SUBJECT ' [email protected]

To see if the Mail Service started: Netstat-tlnup | grep 25

2, at command: Automatically perform some pre-set command actions at the specified date and point of time, belonging to a one-off scheduled task

To host a job that runs in the future time:

Support for using job queues:

The default is a queue;

Save Task: Ctrl+d

At [option] ... Time

Time:

(1) Absolute time

HH:MM,

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

Tomorrow

(2) Relative time

now+ #UNIT

Minute, hour, day, week

(3) Blur time

Midnight

Noon

Teatime

Common options:

-Q queue:at Job queue;

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

-L: View a list of such running jobs in the job queue; equivalent to using the ATQ command;

C At_job_num: Look at the contents of the running job;

-D: Delete the specified job; equivalent to ATRM

Service Script Name:/ETC/INIT.D/ATD

Syntax format: at {hours: minutes} {year-month-day}

ATQ: User queries the currently set at Task List

ATRM: Delete the at task with the specified task number

Example: Application of RELATED commands

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[[email protected] ~]# date

2015年 09月 05日 星期六 18:39:54 CST

[[email protected] ~]# at 18:41 2015-09-05

at> touch/aa

at> <EOT>

job 2 at 2015-09-05 18:41

[[email protected] ~]# atq

2       2015-09-05 18:41 a root

[[email protected] ~]# stat /aa

File: "/aa"

Size: 0               Blocks: 0          IO Block: 4096   普通空文件

Device: fd00h/64768dInode: 14          Links: 1

Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)

Access: 2015-09-05 18:41:01.325106256 +0800

Modify: 2015-09-05 18:41:01.325106256 +0800

Change: 2015-09-05 18:41:01.325106256 +0800

[[email protected] ~]# at 23:59

at> touch/bb

at> <EOT>

job 3 at 2015-09-05 23:59

[[email protected] ~]# atq

3       2015-09-05 23:59 a root

[[email protected] ~]# atrm 3

[[email protected] ~]# atq

Batch

The system chooses to run the specified task when the resource is more idle;

3, Crontab: According to the pre-set time period (minutes, hours, days ...) Repeatedly executes user-specified command actions, which are periodic scheduled tasks

Service Script Name:/etc/init.d/crond

The global configuration file is located at:/etc/crontab

There are two types of recurring tasks:

(1) System cron task; There is no default running user identity, so you need to specify the additional runner;

/etc/crontab

# * * * * * * user-name command to be executed

(2) User Cron Task: Submitted by a user, the default is to run as the submitter, so there is no need to specify the additional runner;

/var/spool/cron/username

# * * * * * command to be executed

crontab command:

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

-u User: Not to manage your own cron task, but to specify the target user's cron task; Root has the ability to manage other users ' cron tasks; default management of their own;

-l:list, list the tasks;

-r:remove to remove all tasks;

-e:edit, edit, open a default editor for the current shell session to edit the cron task table;

Each field Description:

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Special representations of time values:

*: Indicates any time within the range

,: Multiple discontinuous points of time representing the interval

-: Represents a continuous range of time

/: Specify the time frequency of the interval

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例：

0   17  *   *   1-5     周一到周五每天17:00

30  8   8   *   1,3,5   每周一，三，五的8点30分

0   8-18/2*   *   *   8点到18点之间每个两小时

0   *   */3*   *       每隔三天

system default settings and scripts, located in directory/etc/cron.*/

User-defined This is, located in the file/var/spool/cron/user name

Manage Cron Scheduled Tasks:

Edit Scheduled Task: crontab–e {-u user name}

View Scheduled Tasks: crontab–l {-u user name}

Delete Scheduled Task: crontab–r {-u user name}

Attention:

(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;

such as:/bin/cp-rfp/etc//backups/etc-' Date +\%y\%m\%d '

(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

such as:/root/bin/a.sh

Homework:

1, 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;

3 * * 1-6/bin/cp-af/etc//backups/etc-' Date +%y%m%d '

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2, 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 * * 0/bin/cp–af/etc/fstab/backup/fstab-' date +%y%m%d%x '

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3, every night 12 o'clock, get all the lines in the/proc/meminfo file starting with S or M, appended to the/statistics/meminfo.txt file, and the daily message before, to add a similar =============== separator line;

* 0 * * * grep-e ' ^ (s| M) '/proc/meminfo >>/statistics/meminfo.txt&& echo ==================== >>/statistics/ Meminfo.txt

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Linux Scheduled Tasks