linux-Basic Knowledge

Linux Task Scheduler, recurring task execution

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

To run a task periodically: cron

e-Mail Service:

Smtp:simple Mail Transmission protocol for sending mail;

Pop3:post Office Protocol

Imap4:internet Mail Access Protocol

Mailx-send and receive Internet mail

Mua:mail User Agent

MAILX [-S ' SUBJECT '] username[@hostname]

The message body is generated:

(1) give directly, Ctrl+d;

(2) input redirection;

(3) through the pipeline;

Echo-e "How is you?\nhow old is you?" | Mail

Mailx

AT command:

At [option] Time

Time:

hh:mm [YYYY-MM-DD]

Noon, midnight, teatime

Tomorrow

Now+#{minutes,hours,days, or weeks}

Common options:

-Q QUEUE:

-L: Lists jobs waiting to be run in the specified queue; equivalent to ATQ

-D: Deletes the specified job; equivalent to ATRM

-C: View specific job tasks;

-f/path/from/somefile: Reads the task from the specified file;

Note: The execution results of the job are notified to the relevant users by email;

Batch command:

Allow the system to choose its own idle time to perform the tasks specified here;

Recurring Task Scheduler: Cron

Related packages:

Cronie: The main package, provides the Crond daemon and related auxiliary tools;

Cronie-anacron:cronie to monitor the execution of Cronie tasks, such as when a task in Cronie has not run correctly in the past, the Anacron will then initiate this task;

Crontabs: Includes centos to provide system maintenance tasks;

Make sure that the Crond daemon is in a running state:

CentOS 7:

Systemctl Status Crond

..... running ...

CentOS 6:

Service Crond Status

The tasks that are scheduled to be performed periodically are submitted to Crond, which is implemented to the point of operation.

System Cron Task: system maintenance Job

/etc/crontab

User Cron Task:

crontab command

System Cron Task

# 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

Example: Run the echo command at 9:10 in the evening;

* * * * Gentoo/bin/echo "howdy!"

Time notation:

(1) a specific value;

A value in the range of valid values for a given point in time;

(2) *

All values in the range of valid values at a given point in time;

means "every ...";

(3) Discrete value:,

#,#,#

(4) Continuous value:-

#-#

(5) in the specified time range, define the step size:

/#: #即为步长

Example: Echo command every 3 hours;

0 */3 * * * gentoo/bin/echo "howdy!"

User cron:

crontab command definition, each user has a dedicated cron task file:/var/spool/cron/username

crontab command:

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

-L: Lists all tasks;

-E: Editing tasks;

-R: Remove All Tasks;

-I: Used in conjunction with-R to allow users to selectively remove assigned tasks in interactive mode;

-U User: Only root can run, on behalf of the designated users to manage cron tasks;

Note: The results of the operation are notified to the relevant users by email;

(1) COMMAND >/dev/null

(2) COMMAND &>/dev/null

For cron tasks,% has a special purpose, and if you want to use% in a command, you need to escape, but if you put% in single quotes, you can not escape;

Thinking:

(1) How do I run a task at the second level?

* * * * * for min in 0 1 2; Do echo "HI"; Sleep 20; Done

(2) How do I run a task every 7 minutes?

Sleep command:

Sleep Number[suffix] ...

SUFFIX:

S: seconds, default

M: minutes

H: Hours

D: Day

Linux system service Management

Chkconfig--list

Chkconfig--level 3 Network off

Chkconfig--level 345 Network off

Chkconfig--del Network

Chkconfig--add Network

Linux system service Management-SYSTEMD

Systemctl list-units--all

SYSTEMCLT list-units--type=service

A few common service-related commands:

Systemctl Enable Crond.service

Systemctl Disable Crond.service

Systemctl Status Crond.service

Systemctl Stop Crond.service

Systemctl Start Crond.service

Systemctl Restart Crond.service

Systemctl is-enabled Crond.service

[Email protected] ~]# ls-l/etc/systemd/system/multi-user.target.wants/crond.service

lrwxrwxrwx. 1 root root 37 July 05:45/etc/systemd/system/multi-user.target.wants/crond.service-/usr/lib/systemd/system/ Crond.service

Linux system service Management-SYSTEMD

Ls/usr/lib/systemd/system # #系统所有unit, divided into the following types

Service System Services

Target multiple units consisting of groups

Device hardware devices

Mount File System mount point

AutoMount Automatic mount point

Path file or path

Scope is not an external process initiated by SYSTEMD

Slice Process Group

Snapshot Systemd Snapshot

Socket inter-process communication sockets

Swap file

Timer Timer

Operating level:

ls/usr/lib/systemd/system/runlevel*

Liunx System service Management-SYSTEMD

1.unit Related commands

Systemctl list-units//list the running unit

Systemctl list-units--all//list all, including all failed or inactive

Systemctl list-units--all--state=inactive//list inactive unit

Systemctl list-units--type=service//list service with Active status

Systemctl is-acvive Crond.service//See if a service is active

System to manage unit with target for ease of management

Systemctl List-unit-files--type=target

Systemctl list-dependencies multi-user.target//See which unit is under the specified target

Systemctl Get-default//view system default target

Systemctl Set-default Multi-user.target

A service belongs to one type of unit

Multiple unit consists of a target

A target contains multiple service

Cat/usr/lib/systemd/system/sshd.service//Look at the Install section

linux-Basic Knowledge