> For the complete documentation index, see [llms.txt](https://linux-tutorial-cli.gitbook.io/linux-cli-tutorial/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://linux-tutorial-cli.gitbook.io/linux-cli-tutorial/txt-files/file-systems-cocepts/lpic2-201/update-rc.d.md).

# update-rc.d

The `update-rc.d` command is used in Debian-based Linux distributions to manage runlevel configuration for services, particularly those using the SysV init system. Here's a detailed explanation of its purpose and usage:

### Purpose of `update-rc.d`

1. **Service Configuration**:
   * `update-rc.d` is used to install or remove System-V style init script links to the `/etc/init.d/` directory.
   * It allows administrators to control which services should be started or stopped automatically at different runlevels during system startup or shutdown.
2. **Runlevels**:
   * Runlevels represent different operating states of the system, such as single-user mode, multi-user mode with networking, and shutdown.
   * Services can be configured to start (`enable`) or not start (`disable`) at specific runlevels.

### Usage Examples

* **Viewing Current Configuration**:
  * To see the current runlevel configuration of a service:

    ```bash
    update-rc.d <service_name> defaults
    ```

    This command shows the current status of `<service_name>` in each runlevel.
* **Enabling a Service**:
  * To configure a service to start automatically at boot:

    ```bash
    update-rc.d <service_name> defaults
    ```

    This command creates the necessary symbolic links in the appropriate `/etc/rc*.d/` directories to start `<service_name>` in the default runlevels.
* **Disabling a Service**:
  * To prevent a service from starting automatically at boot:

    ```bash
    update-rc.d -f <service_name> remove
    ```

    This command removes the symbolic links from the `/etc/rc*.d/` directories that start `<service_name>`.

### `update-rc.d` with `systemd`

* **Compatibility**:
  * `update-rc.d` is primarily used with SysV init scripts. However, modern Debian-based distributions often use `systemd` as the default init system.
  * `systemd` provides backward compatibility with SysV init scripts and can manage services using `systemctl` commands (`systemctl enable`, `systemctl start`, etc.).

### Conclusion

`update-rc.d` is a useful tool for managing services in Debian-based Linux distributions that use the SysV init system. It provides a straightforward way to configure services to start or stop automatically at different runlevels. As Linux distributions continue to evolve, administrators may encounter both SysV init and `systemd` systems, each requiring different management commands. For `systemd`-based systems, it's recommended to use `systemctl` for managing services for better integration and compatibility with modern Linux features.


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