Command Syntax

  
The systemctl command typically follow this syntax:
 

█ systemctl <command> <unit>

  
It starts with the main call and is followed by these optional parts:
 
  • <command> the action to take.
  • <unit> the service (or resource) to apply that action to.
  
So in short, you simply tell systemctl what action to take on what service.
 

Usage Examples

 
 

Start / Stop a Service

 
Start a service to make it available to users:
 

█ systemctl start <service>

  
After installing a new service, like PlexMedia Server for instance, You'll want to launch the service.
The service will run in background and other users can connect to it.
 

█ sudo systemctl start plexmediaserver

  
Stop a service to make it unavailable to users:
 

█ systemctl stop <service>

  
Stopping a service takes it down, which is useful when you need to peform maintenance or if you want to stop others from being able to connect to it.
 

Autostart a Service on Boot

 
But what happens to a service when you shutdown or reboot?
When the system reboots, your service will be down.
If you want the service to always start, such as a web server that you want to be available 24/7, the solution is to make it load automatically every time the system boots.
 

Enable a service to automatically start on boot:

  
 

█ systemctl enable <service>

  
 

Disable a service to remove it from the autostart list:

  
  █ systemctl disable <service>  
 

Trobleshoot a service

  
Sometimes, I can't connect to one of my servers, like VNC remote access, and I don't know why.
These commands will help you find out what's going on so you can get things running again.
 

Check the status of a service

  
 

█ systemctl status <service>

  
The output will report the service status i.e. Loaded or not and active or inactive.
The soulution maybe to start the service and enable it.
 

Restart a service to stop and start it again:

  
 

█ systemctl restart <service>

  
What if you need to change the configuration for a service, but you don't want to bring it down because it will distrupt your users' activity? For instance, maybe you have a Postfix email server, and are testing a lot of settings over and over.
In this case, you can use the reload command instead.
 

█ systemctl reload <service>

  
 

Kill a service to terminate it forcefully:

  
 

█ systemctl kill <service>

  
 

List All Services

 
if you want to manage or troubleshoot a service but don't know what name it goes by on your system, the systemctl command can be used to figure it out.
If you enter systemctl command with no parameters,you'll get a long lisst of everything initialized on your system, like kernel modules and virtual RAM disks. This can be 200 lines (or more), and in my experience,that's often information overload.
Let's say you're only interested in what services are on the system. You can filter systemctl's output to narrow down what you see.
 

List services only:

  
 

█ systemctl list-units --type=service

  
This command filters the output to show services only and is more readable.
But maybe you want to narrow that list down even more. ProbabIy you're only interested in learning about services that are active, use these next command.
 

List running services to see which ones have been started:

  
 

█ systemctl list-units --type=service --state=running