:
cd /usr/lib/systemd/system
This are default services.
The changes should be done into:
/etc/systemd
Here are service scripts and will overwrite the one from /usr/lib/systemd/system
The basic unit of the systemd are the services from /usr/lib/systemd/system
Here is an example of service httpd.service.
Can make everything as service and start it.
The buttom line show how service should be started.
It should be started by target.
To manage service:
# systemctl status httpd
stop – stop the service
disable – take it out from startup procedure of OS.
System stated are TARGETS.
Those are in /etc/
or in /usr/lib/systemd/system
There are 2 targets:
multiuser – server without GUI
graphical – GUI
When enable a server, a symbolic link is created in /usr/lib/systemd/system/multi-user.target.wants/.
the rest are into:
/etc/systemd/system/multi-user.target.wants
To define, in systemd is a default.target which decide what will start. This can be change by changing the symbolic link.
Check active targets:
# systemctl list-units –type=target
We have the service which is responsible to start specific things from OS. Also is the targets which is a collection of a services. The target itself define dependencies with other targets in order to be sure that all requirements are started as need it and in order to put services into a target, will have to create a wants. A wants is a symbolic link which is created automatically when is issue the command “systemctl enable serviceName”
Switching Between systemd Targets
Check the status target:
# systemctl list-units -type=target
Change to minimum mode:
# system isolate rescue.target
Check the targets:
# systemctl list-units -type=target
From rescue mode there is the only option to exit and reboot from grub:
# exit
From boot menu:
type: e (from edit)
go to line which starts with “linux16”
At end of line add: systemd.unit=rescue.target
ctrl+x to start system.
Type password to get access.
From rescue mode press “ctrl+d” in order to go to GRUB and exit.
EMERGENCY.TARGET
Add at end of line linux16:
systemd.uni=emergency.target
ctrl+x
enter the root passwd
# systemctl list-units –type=target
To start the default target:
# systemctl default