Managing System Services in Linux | systemctl Command

Systemd is a modern system and service manager for Linux that serves as the core initialization process (PID 1). It controls system startup, manages background services, and ensures efficient system operation.

• Starts automatically as the first process when the Linux kernel boots.
• Manages all other processes during system runtime.
• Uses parallelization to launch multiple services simultaneously, speeding up boot time.
• Organizes system components into “units” such as services, sockets, devices, mounts, and timers.
• Controlled via the systemctl command-line tool (start, stop, enable, disable, and check services).

Example: Starting and Stopping a System Service in Linux:

Syntax:

systemctl start [service_name]
systemctl stop [service_name]
systemctl status [service_name]

Example with Apache Web Server

Commands:

systemctl start apache2
systemctl status apache2

Output:

• The command systemctl start apache2 starts the Apache web server service.
• The command systemctl status apache2 displays the current status of the Apache service.

Command:

systemctl stop apache2
systemctl status apache2

Output:

• The command systemctl stop apache2 is used to stop the Apache web server.
• The command systemctl status apache2then checks whether the service is still running or stopped.

Syntax of `systemctl` command in Unix

systemctl [command] [service]

• [command] = The action we want to perform (start, stop, enable, disable, etc.)
• [service] = The name of the service we want to perform the action on.

Options available in `systemctl` command in Unix

Managing System Services in Linux

1. Enabling and Disabling Services

Enabling a Service

• Enables the Apache web server to start automatically at system boot.

Syntax:

systemctl enable [service]

Example:

sudo systemctl enable apache2

Output:

Disabling a Service

• Disables the Apache web server, preventing it from starting automatically at boot.

Syntax:

systemctl disable [service]

Example:

sudo systemctl disable apache2

Output:

2. Viewing the Status of a Service

• Displays the "current status" of Apache (whether it’s _active_, _inactive_, _running_, or _failed_).

Syntax:

systemctl status [service]

Example:

sudo systemctl status apache2

Output:

3. Restarting and Reloading Services

Restarting a Service

• Restarts the Apache web server, applying any configuration or update changes.

Syntax:

systemctl restart [service]

Example:

sudo systemctl restart apache2

Output:

Reloading a Service

• Reloads Apache configuration without completely stopping the service, useful after minor config edits.

Syntax:

systemctl reload [service]

Example:

sudo systemctl reload apache2

Output:

4. Masking and Unmasking Services

Masking a Service

• Prevents the Apache service from being started manually or automatically, even if required by other services.

Syntax:

systemctl mask [service]

Example:

sudo systemctl mask apache2

Output:

Unmasking a Service

• Allows the Apache service to be started or enabled again.

Syntax:

systemctl unmask [service]

Example:

sudo systemctl unmask apache2

Output:

5. Changing the Default Target

• Sets the system to boot into the graphical (GUI) mode by default instead of command-line mode.

Syntax:

systemctl set-default [target]

Example:

sudo systemctl set-default graphical.target

Output:

6. Listing Unit Files

• Lists all available unit files on the system, showing which are enabled, disabled, or static.

Syntax:

systemctl list-unit-files

Output:

7. Masking and Unmasking Unit Files

Masking a Unit File

• Prevents the Apache unit file from being started or enabled under any condition.

Syntax:

systemctl mask [unit-file]

Example:

sudo systemctl mask apache2.service

Output:

Unmasking a Unit File

• Restores the ability to start or enable the Apache unit file again.

Syntax:

systemctl unmask [unit-file]

Example:

sudo systemctl unmask apache2.service

Output:

Also Check:

• How to Start, Stop and Restart Services in Linux Using systemctl Command
• How to mask a systemd unit in Linux?