# Cheatsheet & Examples: systemctl systemctl is a command-line utility used to control the systemd system and service manager. It allows users to manage system services, check their status, enable/disable them at boot, and more. ## Check the status of a service Example Usage: `systemctl status sshd` What it does: Displays the current status of the `sshd` service, including whether it is active, running, or failed. Command-line Arguments Explained: - `status`: The main command to check the status of a unit. - `sshd`: The name of the service unit (e.g., SSH daemon). ## Start a service Example Usage: `systemctl start httpd` What it does: Starts the `httpd` service immediately. Command-line Arguments Explained: - `start`: The command to initiate the specified service. - `httpd`: The service unit to be started (e.g., Apache web server). ## Stop a service Example Usage: `systemctl stop nginx` What it does: Stops the `nginx` service. Command-line Arguments Explained: - `stop`: The command to terminate the specified service. - `nginx`: The service unit to be stopped (e.g., NGINX web server). ## Restart a service Example Usage: `systemctl restart postfix` What it does: Restarts the `postfix` service, stopping and then starting it again. Command-line Arguments Explained: - `restart`: The command to stop and then start the specified service. - `postfix`: The service unit to be restarted (e.g., mail transfer agent). ## Reload a service configuration Example Usage: `systemctl reload docker` What it does: Reloads the configuration of the `docker` service without restarting it. Command-line Arguments Explained: - `reload`: The command to reapply the service's configuration. - `docker`: The service unit to reload (e.g., container runtime). ## Enable a service to start at boot Example Usage: `systemctl enable crond` What it does: Enables the `crond` service to start automatically during system boot. Command-line Arguments Explained: - `enable`: The command to configure the service for automatic startup. - `crond`: The service unit to enable (e.g., cron daemon). ## Disable a service from starting at boot Example Usage: `systemctl disable cups` What it does: Disables the `cups` service from starting automatically at boot. Command-line Arguments Explained: - `disable`: The command to prevent the service from starting automatically. - `cups`: The service unit to disable (e.g., print spooler). ## List all active service units Example Usage: `systemctl list-units --type=service --state=running` What it does: Lists all active service units that are currently in the "running" state. Command-line Arguments Explained: - `list-units`: Displays the status of units. - `--type=service`: Filters the output to show only service units. - `--state=running`: Displays only units in the "running" state. ## List all unit files Example Usage: `systemctl list-unit-files` What it does: Shows all unit files on the system with their loading and activation status. Command-line Arguments Explained: - `list-unit-files`: Displays a list of all unit files. ## Reload systemd configuration Example Usage: `systemctl daemon-reload` What it does: Reloads the systemd manager configuration after changes to unit files. Command-line Arguments Explained: - `daemon-reload`: Forces systemd to re-read configuration files. ## Check if a service is active Example Usage: `systemctl is-active sshd` What it does: Reports whether the `sshd` service is active (e.g., "active" or "inactive"). Command-line Arguments Explained: - `is-active`: The command to check the activation state of a unit. - `sshd`: The service unit to evaluate. ## Check if a service is enabled Example Usage: `systemctl is-enabled firewalld` What it does: Checks if the `firewalld` service is configured to start at boot. Command-line Arguments Explained: - `is-enabled`: The command to verify a unit’s enablement status. - `firewalld`: The service unit to check. ## View the content of a unit file Example Usage: `systemctl cat sshd.service` What it does: Prints the contents of the `sshd.service` unit file for inspection. Command-line Arguments Explained: - `cat`: The command to output a unit file's content. - `sshd.service`: The specific unit file to display. ## List dependencies of a service Example Usage: `systemctl list-dependencies nginx` What it does: Displays the dependency hierarchy for the `nginx` service. Command-line Arguments Explained: - `list-dependencies`: Shows dependencies of the specified unit. - `nginx`: The service unit to analyze for dependencies. ## Show failed units Example Usage: `systemctl --failed` What it does: Lists all units that have failed to load or start. Command-line Arguments Explained: - `--failed`: Filters units to show only those in a failed state. ## Reset failed status of a unit Example Usage: `systemctl reset-failed systemd-journald` What it does: Clears the "failed" state flag for the `systemd-journald` unit. Command-line Arguments Explained: - `reset-failed`: Clears the failed status of a unit. - `systemd-journald`: The unit to reset. ## Disable terminal paging Example Usage: `systemctl --no-pager status nginx` What it does: Prevents the output of the `status` command from being paginated. Command-line Arguments Explained: - `--no-pager`: Disables the use of a pager (e.g., `less`) for output. - `status`: Checks the status of the specified unit. - `nginx`: The service unit to check. ## Check logs for a service Refer to [`journalctl`](https://tech.mrleong.net/cheatsheet-examples-journalctl). ## Show unit file details Example Usage: `systemctl show sshd` What it does: Prints detailed properties of the `sshd` unit file. Command-line Arguments Explained: - `show`: Outputs detailed information about a unit. - `sshd`: The service unit to inspect. ## Check the unit file’s state Example Usage: `systemctl is-failed nginx` What it does: Checks if the `nginx` service has failed to start or load. Command-line Arguments Explained: - `is-failed`: Reports whether the specified unit has failed. - `nginx`: The service unit to check.