In most operating systems, user data, system data, and configuration files can become intermingled, which can make them challenging to manage.
Figure 1: Without stateless, user and system files become mixed on the filesystem over time.
|CL-ATTR| has a stateless design philosophy with the goal to provide an :abbr:`OS (operating system)` that functions without excessive user configuration or customization. Stateless in this context does not mean ephemeral or non-persistent.
To accomplish a stateless design, the |CL| filesystem hierarchy is separated between user-owned areas and |CL|-owned areas.
Figure 2: With stateless, user and system files are separated on the filesystem.
Files under the :file:`/usr` directory are managed by |CL| as system files (except :file:`/usr/local`). Files written under the :file:`/usr` directory by users can get removed through system updates with :ref:`swupd <swupd-guide>`. This operating assumption allows |CL| to verify and maintain integrity of system files.
Files under the :file:`/usr/local`, :file:`/etc/`, :file:`/opt`, :file:`/home`, and :file:`/var` directories are owned and managed by the user. A freshly installed |CL| system will only have a minimal set of files in the :file:`/etc/` directory and software installed by |CL| does not write to :file:`/etc`. This operating assumption allows |CL| users to clearly identify the configuration that makes their system unique.
With stateless separation, default software configurations are read in order from predefined source code, |CL| provided defaults, and user-provided configuration.
Software in |CL| provides default configuration values so that it is immediately functional, except for some that require additional configuration.
If an upstream software puts default configurations in multiple locations such as :file:`/usr/` and :file:`/etc`, it will be modified by the |CL| distro to comply with the stateless design. Also, some default configurations may be modified to close security loopholes. Defaults will reside under :file:`/usr/share/defaults`. These files can be referenced as templates for customization.
For example, after installing the httpd bundle for Apache web server, its default configurations appear in the :file:`/usr/share/defaults/httpd/` directory.
If a configuration needs to be changed, the appropriate file should be modified by the user under :file:`/etc/`. If the configuration file does not already exist, it can be created in the appropriate location.
User-defined configuration files should contain the minimal set of desired changes and rely on default configuration for the rest.
For example, a customized Apache configuration can be used instead by:
Install the Apache web server bundle.
sudo swupd bundle-add httpd
Create the destination directory for the configuration.
sudo mkdir /etc/httpd
Copy the default configuration as a reference template.
sudo cp /usr/share/defaults/httpd/httpd.conf /etc/httpd/
Make any desired modifications to the configurations.
sudoedit /etc/httpd/httpd.conf
Reload the service or reboot the system to pickup any changes.
systemctl daemon-reload httpd && systemctl restart httpd
This pattern can be used to modify the configurations of other programs too. The stateless man page has application-specific examples.
One advantage of the stateless design is that the system defaults can be easily restored by simply deleting everything under :file:`/etc/` and :file:`/var`.
Running the commands below effectively performs a system reset as if it was just installed:
sudo rm -rf /etc
sudo rm -rf /varIn other Linux distributions, this can be a catastrophic action that may render a system unable to boot and/or inaccessible.