Overview of systemctl
systemd is an init system that manages the boot process of the system and controls all services (daemons) that run in the background after the system boots. `systemctl` provides an interface to manipulate these functionalities of systemd from the command line. Various commands such as `service`, `chkconfig`, `reboot`, and `shutdown` have been integrated into `systemctl`.
Understanding systemd Units
systemd abstracts everything it manages into a concept called 'Unit'. Each unit represents a specific service, mount point, device, etc. The most commonly dealt unit types include `service unit (.service)`, `socket unit (.socket)`, `mount unit (.mount)`, `device unit (.device)`, and `target unit (.target)`. Typically, the `.service` extension is omitted in use.
Key Roles of systemctl
- Check Service Status: Identify running services, enabled services, failed services, etc.
- Control Services: Start, stop, restart, and reload (re-read configuration) services.
- Set Automatic Start for Services: Configure services to start automatically at system boot or disable this setting.
- System Power Management: Reboot, power off, or suspend the system.
- Manage Unit Files: Check and modify locations, dependencies, etc. of unit files.
Main systemctl Command Options
`systemctl` provides a rich set of options for various functions such as service management, system power control, and unit file management. Most service-related commands require `sudo` privileges.
1. Service Status and Control
2. Set Service Auto-Start
3. System Power Management
4. Unit Files and Lists
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Description:
`systemctl` Executes the command.
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Usage Examples
Learn how to effectively manage services on systemd-based systems through various usage examples of the `systemctl` command.
Check Status of Web Server (Nginx)
systemctl status nginx.serviceCheck detailed information about whether the Nginx web server is currently running, inactive, or encountering errors.
Start MySQL Service
sudo systemctl start mysql.serviceStarts the MySQL database service.
Restart SSH Service
sudo systemctl restart sshd.serviceRestarts the SSH (Secure Shell) service. Useful after changing the configuration file.
Set Apache Web Server to Start Automatically
sudo systemctl enable apache2.serviceConfigures the Apache web server to start automatically at system boot.
Check List of All Active Services
systemctl list-units --type=service --state=activeLists all service units in 'active' status (currently running or ready) on the current system.
Reboot System via systemd
sudo systemctl rebootSafely reboots the system in the most recommended way.
View Content of Specific Service Unit File
systemctl cat redis-server.serviceCheck the contents of the Redis service's systemd unit file (e.g., `/etc/systemd/system/redis.service`) to understand how the service operates.