LINUX20180511 eight-week class cron chkconf systemd unit target

Eight week class (May 11)

10.23 Linux Task Scheduler cron
10.24 Chkconfig Tools
10.25 SYSTEMD Management Services
10.26 Unit Introduction
10.27 Target Introduction
Extended
1. Anacron http://blog.csdn.net/strikers1982/article/details/4787226
2. XINETD (the default machine does not install this service, requires Yum install xinetd installation) http://blog.sina.com.cn/s/blog_465bbe6b010000vi.html
3. SYSTEMD Custom Startup script http://www.jb51.net/article/100457.htm

Linux Task Scheduler

It could be a shell script, or it could be a separate command. Whatever the form, it takes some time to execute, so you need to determine a time.

Configuration file for Task Scheduler Etc/crontab

Defines the variables, environment variables, command path mailto who sent the message, and the format. If you do not write the user, the default is root

Define commands for a Linux task plan

crontab-e syntax is the same as Vim

For example, set a 3 o'clock in the morning task:

Explain:

0 3 * * *0 points 3 points per day per month daily execution

The/bin/bash description is to execute the shell script after the/user/local/sbin/123.sh followed by the script to execute and then write to log because it is executed every day, so the append is followed by the error log is appended to this file

You can also use ranges to represent time

0 3 1-10 */2 2,5

3:0 A.M. 1-10, */2 is divisible by 2 is the leap month Tuesday Friday

Then start Crond This service to use this task plan

Systemctl Start Crond

Then use to check if the process is started

Or use Systemctl status Crond to check the status of Crond

Systemctl Stop Crond Stop Crond

View current Task Schedule commands

Crontab-l

Delete the current task schedule

Crontab-r

View task schedules for a specified user

Crontab-u root-l

Attention:

1. Sometimes it is possible to write a script that uses a command rather than an absolute path to the command, which may result in an inability to execute.

2. Write an additional log for each task plan, so there are traces to follow.

3. The file location of the task plan is root under the cron root of the/var/spool/cron/root corresponding user, and the other user's cron has the corresponding user name. So you can copy this file directly to another location for backup.

Linux system service Management-chkconfig

So-called crontab firewalld and so on are services, all services so need to have a service management tool.

CENTOS6 is chkconfig, but 7 is equally compatible.

Display the service

Chkconfig--list

To explain, it looks like there are only 2 processes at the moment, so it's strange, where do the other processes go?

Look at the above explanation, this command value shows the SYSV service, does not include the SYSTEMD service, meaning 6 and the previous version of the service management mechanism is sysv,7 with systemd, so SYSTEMD is 7 and later version of the service manager. This very important process can also be seen from the top command.

Where is the specific location path of the Chkconfig managed service?

/etc/init.d/later in the configuration of Ngix MySQL may also need to put the startup script to this path and then use Chkconfig to manage

Can close the service

Chkconfig Network off

0-6 represents a different service level.

0--shut down the machine

Single user centos6 and previous versions

2--is less than 3. One NFS Service

3--Multi-user mode with no image

4--retention Level

5--multi-user with graphical interface

6--restart

There is no level of CENTOS7. 6 and previous versions can define the RunLevel by changing the configuration file/etc/inittab.

Chkconfig can specify that a level is turned on or off

Chkconfig--level 3 Network off/on

You can also put a custom script in the service, you must put the script in the/ETC/INIT.D directory

Then use the command

Chkconfig--add New Service

Of course, the format of this new service file must meet some criteria. Let's take a look. The following two lines are required

Chkconfig:

Description

The above comment means that the service must be started or shut down at run level 2,3,4,5, the priority of the boot is 90, and the priority of the shutdown is 10. 90 is the start priority, 10 is the stop priority, the priority range is 0-100, the greater the number, the lower the priority.

There will be a deletion if it is added

Chkconfig--del Service Name

The service is deleted, the files are still there.

Linux system service Management--SYSTEMD (CENTOS7 Service management mechanism)

commands to display all types of services

Systemctl list-units--all--type=service

If you don't add--all, you won't list the inactive.

Cron service boot/No boot

Systemctl enable/disable Crond

View cron Status

Systemctl Status Crond

Stop cron Service

Systemctl Stop Crond

Start the Cron service

Systemctl Start Crond

Restart

Systemctl Restart Crond

Check that the Cron service is booting up

Systemctl is-enabled Crond

The contents of the Cron configuration file can also be obtained from the above

From the right soft link to the left, to the right is the true file path

A soft link will be generated after the enable, and the soft link will not be disable.

Ls/user/lib/systemd/system is the system, all the unit. Below are the different types of classifications

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

Snapshots of snapshot systemd

Swap swap files

Timer Timer

CentOS7 does not have a 0-6 operating level, but there are runlevel similarities.

Ls-l runlevel*

It was also soft-linked. You can see from the back what exactly it means.

such as Poweroff Shutdown Rescue Rescue Multi-User multi-user graphical graphical reboot restart

You can see that the type of command is target

systemctl list-units lists the running unit

systemctl list-units--all list all, including failed or inactive unit

systemctl list-units--all--state=inactive lists the unit of inactive

systemctl list-units--type=service List service with Active status

systemctl is-active Crond.service See if a service (cron here) is active

What exactly is the relationship between target and unit?

Target is the unit's collection, the unit is managed, and the system manages the unit with target for ease of management.

View units of target type

Systemctl List-unit-files--type=target

See which unit is under the specified target

systemctl list-dependencies multi-user.target Many users of this target under the unit, so that the target can also continue to have target

View the system default target

Systemctl Get-default

To view the system default target file

ls-l/etc/systemd/system/default.target can see actually also a soft link, real file in/lib/systemd/system/multi-user.target

Set the system default target

Systemctl Set-default multi-user.target After setting up soft links will also change

A service belongs to one type of unit multiple unit consisting of a target with a target containing multiple service

Cat/usr/lib/systemd/system/sshd.service View the specifics of the sshd service

"Install"

Wantedby is multi-user.target need, that is to say it belongs to the target multi-user

LINUX20180511 eight-week class cron chkconf systemd unit target