34. Linux System Task Scheduler cron, chkconfig Tools, SYSTEMD Management Services, Unit introduction, Target introduction
I. Linux system Task Scheduler cron
crontab command: Use this command for the operation of the task scheduling feature. Options:
-U: Specifies that a user, without-u, is the current user.
-E: Make a task plan.
-L: Lists the task schedule.
-R: Deletes the task schedule.
Configuration file for Task Scheduler:/etc/crontab
There are five fields in a file.
From left to right: minutes, hours, days, months, weeks, users, commands.
You can not specify that the user is root.
# CRONTAB-E//write a task plan, the actual use of Vim opened the crontab configuration file.
The /var/spool/cron/username of the configuration file that is opened at this time. (If the user is root, then cron is root). can not VI edit this file, can only be edited with crontab-e , otherwise error.
* denotes all. such as weekly, daily, monthly.
0 3 * * */bin/bash/usr/local/sbin/123.sh >>/tmp/123.log 2>>/tmp/123.log
For example, execute a script.
Each field can write a range:
0 3 1-10 */2 2,5/bin/bash/usr/local/sbin/123.sh >>/tmp/123.log 2>>/tmp/123.log
1-10 days, divisible by 2 months, Tuesday and Friday
# Systemctl Start Crond starting the Crond service, to use the Task Scheduler, it will start.
# PS aux |grep cron
Root 589 0.0 0.0 126236 1612? Ss 01:51 0:00/usr/sbin/crond-n
Root 1460 0.0 0.0 112676 980 pts/0 s+ 04:26 0:00 grep--color=auto cron
This process indicates that the service has been started.
# SYSTEMCTL Status Crond view its status and if it starts, it displays the green active (running). If it does not start, no font has color display, inactive (dead).
in the configuration file Command writes absolute path when writing a task plan , otherwise it may not be performed because it is not in the environment variable.
Each time you write a task plan, the correct log and error log are appended to the save. When something goes wrong, it can be traced.
Second, Linux system service management-chkconfig
The Service Management tool on CENTOS6 is chkconfig, and all of the preset services in the system can be seen through/ETC/INIT.D. Centos7 no longer extends CENTOS6 's service management program anymore. So there are only a few files.
# LS/ETC/INIT.D all pre-set service directories
Functions Netconsole Network README
# chkconfig--list List all services and their opening status at each level
Note: This output shows only the SysV service and does not contain
Native SYSTEMD services. SysV Configuration Data
May be overwritten by native SYSTEMD configuration.
To list the SYSTEMD service, execute ' systemctl list-unit-files '.
To view the services enabled on the specific target, perform
' Systemctl list-dependencies [target] '.
Netconsole 0: Off 1: Off 2: Off 3: Off 4: off 5: off 6: Off
Network 0: Off 1: Off 2: Open 3: Open 4: Open 5: Open 6: Off
CENTOS6 and formerly SYSV service Management, CENTOS7 is SYSTEMD service management.
Level: System boot level (usage prior to 7, 7 not strictly level sensitive)
0: Shutdown status.
1: Single-user mode
2: Less than 3 one NFS service
3: Multi-user mode with no graphics
4: Reserved state, custom for user
5: Multi-user mode with graphics
6: Restart
# chkconfig--level 3 Network off
--LEVEL Specifies the level, then the service name, then off or on.
You can also specify multiple levels,--level 345.
You can also omit the level, which defaults to 2, 3, 4, and 5 operations.
Services must be in the/etc/init.d/directory to add services.
Add service, Chkconfig--add Network (service name)
Delete Service, Chkconfig--del Network
Can be found in Chkconfig--list.
In-file format these two points must have, otherwise unrecognized
# chkconfig:2345 10 90
# description:activates/deactivates all network interfaces configured to \
# start at boot time.
Third, SYSTEMD Management services
# systemctl list-units--all--type=service list system all services
Common commands:
# Systemctl enable Crond to enable a service to boot (. Service can be omitted)
# systemctl Disable crond do not let service boot up
# SYSTEMCTL Status Crond view service status
# Systemctl Start Crond start a service
# Systemctl Stop Crond Stop a service
# systemctl Restart Crond restart a service
# systemctl is-enabled crond Check if a service is booting
Iv. introduction of the unit
# Ls/usr/lib/systemd/system There are a number of files, categorized into the following categories:
Service: System Services
Target: A group of more than one unit
Device: Hardware Device
Mount: File system mount point
AutoMount: Automatic mount point
Path: File or Path
Scope: External process not initiated by SYSTEMD
Slice: Process Group
Snapshot:systemd Snapshot
Socket: Socket for interprocess communication
Swap:swap file
Timer: Timer
Each type of file is a unit, and it is these units that make up the various resources of the system (individual services, individual devices, etc.)
Unit-related commands:
# systemctl List-units//list the unit that is running (active)
# Systemctl List-units--all//list all unit (including failed, inactive)
# systemctl list-units--all--state=inactive //List all inactive's unit
# systemctl List-units--all--type=service//List all status of service
# Systemctl List-units--type=service//list service with Active status
# Systemctl Is-active crond.service//See if a unit is active
Five, Target introduction
Similar to the boot level in CENTOS6, Target supports multiple simultaneous booting. It is a combination of multiple unit, the system starts is to start a number of unit,target is used to manage these unit.
# Systemctl List-unit-files--type=target//View all target of current system
# Systemctl List-dependencies multi-user.target//View a target contains all the unit, in a tree-shaped column.
# Systemctl Get-default//view system default target
# Systemctl Set-default multi-user.target//set default target
Connection between service, unit, and Target:
1) A service belongs to a unit
2) Multiple unit together to form a target
3) A target contains multiple service that can view the contents of the [Install] section of the file/usr/lib/systemd/system/sshd.service, which defines which target the service belongs to.
34. Linux System Task Scheduler cron, chkconfig Tools, SYSTEMD Management Services, Unit introduction