03-SYSTEMD-Tools.md

SYSTEMD Tools to Manage SYSTEMD service

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In this lecture we will explore two major SYSTEMD tools:

• SYSTEMCTL
• JOURNALCTL

SYSTEMCTL

• Systemctl is the main command used to manage services on a SYSTEMD managed server.

• It can be used to manage services such as START/STOP/RESTART/RELOAD as well as ENABLE/DISABLE services during the system boot.

• It is also used to LIST AND MANAGE UNITS and LIST AND UPDATE TARGETS

  

### Systemctl Commands 

- To start a service use the start command, for example to start a docker service use **`systemctl start docker`**

  ```
  [~]$ systemctl start docker
  ```

- To stop a service use the stop command, for example to stop a docker service use **`systemctl stop docker`**

  ```
  [~]$ systemctl stop docker
  ```
- To restart a service use the restart command, for example to restart a docker service use **`systemctl restart  docker`** this will stop and start again.

  ```
  [~]$ systemctl restart docker
  ```
- To reload a service use the reload command, for example to reload a docker service use **`systemctl reload docker`**, this will reload all the configuration without interrupting the normal functionaltiy of the service

  ```
  [~]$ systemctl reload docker
  ```
- To enable a service and make it persistent accross reboots use the enable command, for example to enable a docker service use **`systemctl enable docker`**
  
  ```
  [~]$ systemctl enable docker
  ```

- To disable a service at boot use the disable command, for example to disable a docker service use **`systemctl disable docker`** command.
  
  ```
  [~]$ systemctl disable docker
  ```

- To know the status of the service use **`systemctl status docker`** command. This command provided the state of the service. If running properly is should show **`active (running)`** state as shown in screenshot below.

  ```
  [~]$ systemctl status docker
  ```

- Besides **`active (running)`** state there are few other state that you should be aware off.
    
  ![Other](../../images/otherstate.PNG)

- Running **`systemctl daemon reload`** command after making changes to service unit file reloads the system manager configuration and makes the systemd aware of the changes. 

- To edit the service file use command **`systemctl edit project-mercury.service --full`** this will open a text editor, you can make the changes and re-write the settings as needed, making changing this way applied immediately without running the **`systemctl daemon reload`** command
  
  ```
  [~]$ systemctl daemon-reload
  ```
  ```
  [~]$ systemctl edit project-mercury.service --full
  ```
- To see the current runlevel use **`systemctl get-default`**
  
  ```
  [~]$ systemctl get default
  ```

- To change the runleve to a different target use  **`systemctl set-default multi-user.target`**
  
  ```
  [~]$ systemctl set-default multi-user.target
  ```

- To list all the units that systemd has loaded use **`systemctl list-units --all`**, this lists all the unit which are active, inactive or anyother state.
  
  ```
  [~]$ systemctl list-units --all
  ```

- To list only active units use **`systemctl list-units`** command
  
  ```
  [~]$ systemctl list-units
  ```

JOURNALCTL

• Journalctl is a command for quering/viewing logs collected by systemd.

• The systemd-journald service is responsible for systemd’s log collection, and it retrieves messages from the kernel systemd services, and other sources.

• Very useful when you are troubleshooting issues with systemd services.

  

• Using journalctl commands print all the log entries from oldest to the newest.

• Using journalctl -b command print all the logs from the current boot.

• Using journalctl -u docker.service command print all the logs specific to the unit specified, for example docker in this case.

  [~]$ journalctl
  

  [~]$ journalctl -b
  

  [~]$ journalctl -u docker.service 
  

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