Linux Task Scheduler (AT,CRONTAB)

Tasks scheduled in Linux, scheduled to perform certain tasks or periodically perform certain tasks

Task Schedule:

Perform a task at a time in the future: at, Batch

To perform a task periodically: crontab

After completing the task, Liunx will send a message to the current user

Email service: Smtp:simple Mail Transmission protocol

Paths in Linux:/var/spool/mail/username

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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]

AT command: 650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M01/72/DD/wKioL1XvA5awEl4rAAHkjuMBAgA441.jpg "/>

To host a job that runs in the future time:

Support for using job queues:

The default is a queue;

CTRL+D: Submitting a task

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

Batch

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

Crontab: Recurring Task Schedule

Daemon: Crond

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

Vim command

# Example of Job definition:

#.----------------Minute (0-59)

# | .-------------Hour (0-23)

# |  | .----------Day of Month (1-31)

# |  |  | .-------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

# |  |  |  | |

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

7 fields:

Top 5 fields: Point in time

User-name: Run the task as a user

command to being executed: to run a task

(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

VIM command; not recommended

crontab Command: Recommended

# Example of Job definition:

#.----------------Minute (0-59)

# | .-------------Hour (0-23)

# |  | .----------Day of Month (1-31)

# |  |  | .-------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

5 Time points:

Minutes: valid value range 0-59;

Hours: 0-23

Day: 1-31

Month: 1-12

Weeks: 0-7

Note: The date of the month and the number of weeks, not recommended to use at the same time;

For example:

6* * * *

Time notation:

*: Each time point in the valid value range of the time point;

-: A specific continuous time range, 3-7

,: A discrete point in time, 3,5,7

/#: The amount of time in a valid time frame, for specifying the frequency;

1-30/4,*/4

5 */3* * */bin/echo "howdy"

5 7 * * 1-5/bin/echo "Howdy"

crontab command:

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

-uuser: Instead of managing its own cron task, it is the cron task of the specified target user; only Root has permission to manage other users ' cron tasks; By default it manages its 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;

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;

(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

Practice:

1. Every Monday to Saturday 3:20 A.M., run the CP command to save the/etc/directory, storage location is/BACKUPS/ETC-YYYY-MM-DD;

~]# crontab-l

3 * * 1-6/bin/cp/etc-rpf/backups/etc-' file\%y-\%m-\%d '

2. Every Sunday 2:30 A.M., run the CP command to back up the/etc/fstab file with a storage location of/BACKUP/FSTAB-YYYY-MM-DD-HH-MM-SS

~] #crontab-L

2 * * 7/bin/cp/etc/fstab/backup/fstab-' file\%y-\%m-\%d-\%h-\%m-\%s '

3. Every night 12 o'clock, obtain 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;

~] #crontab-L

0 * * * echo "===============" >>/proc/meminfo | Egrep "^s|^m"/proc/meminfo >>/statistics/meminfo.txt

This article is from the "Lost Lamb" blog, please be sure to keep this source http://humingfeeling.blog.51cto.com/386110/1692946

Linux Task Scheduler (AT,CRONTAB)