systemctl

systemctl is a command-line utility used to interact with systemd, the init system and service manager used by many Linux distributions. systemctl provides a comprehensive interface for managing services, inspecting the state of the system, and controlling system behavior.

Overview of systemctl

Purpose

systemctl is used to:

• Manage system services (start, stop, restart, enable, disable).

• Query and change system states.

• Control system boot process.

• Inspect logs and system status.

Basic Usage

The general syntax for systemctl commands is:

systemctl [options] <command> [name]

• [options]: Various options to control the behavior of systemctl.

• <command>: The specific action to perform (e.g., start, stop, status).

• [name]: The name of the service, unit, or target to act upon.

Common systemctl Commands

1. Starting and Stopping Services

   • Start a service:

     systemctl start <service_name>

     Example:

     systemctl start apache2

   • Stop a service:

     systemctl stop <service_name>

     Example:

     systemctl stop apache2

   • Restart a service:

     systemctl restart <service_name>

     Example:

     systemctl restart apache2

   • Reload a service (if the service supports it):

     systemctl reload <service_name>

     Example:

     systemctl reload apache2

2. Enabling and Disabling Services

   • Enable a service (start at boot):

     systemctl enable <service_name>

     Example:

     systemctl enable apache2

   • Disable a service (do not start at boot):

     systemctl disable <service_name>

     Example:

     systemctl disable apache2

   • Check if a service is enabled:

     systemctl is-enabled <service_name>

     Example:

     systemctl is-enabled apache2

3. Checking Service Status

   • Get the status of a service:

     systemctl status <service_name>

     Example:

     systemctl status apache2

4. Listing Services and Units

   • List all services:

     systemctl list-units --type=service

   • List all units (including services, sockets, targets, etc.):

     systemctl list-units

   • List failed units:

     systemctl --failed

5. Managing System States

   • Reboot the system:

     systemctl reboot

   • Power off the system:

     systemctl poweroff

   • Suspend the system:

     systemctl suspend

   • Hibernate the system:

     systemctl hibernate

6. Masking and Unmasking Services

   • Mask a service (prevent it from starting):

     systemctl mask <service_name>

     Example:

     systemctl mask apache2

   • Unmask a service (allow it to start):

     systemctl unmask <service_name>

     Example:

     systemctl unmask apache2

Advanced Usage

1. Viewing Logs with journalctl

   • View logs for a specific service:

     journalctl -u <service_name>

     Example:

     journalctl -u apache2

2. Editing Unit Files

   • Edit a service unit file:

     systemctl edit <service_name>

   • Reload systemd manager configuration after editing unit files:

     systemctl daemon-reload

Conclusion

systemctl is an essential tool for managing and controlling services and system states on a Linux system running systemd. It provides powerful capabilities for administrators to maintain and troubleshoot system services effectively.