In most operating systems, files can become intermingled with user and system data and configurations.

Stateless: User and system files mixed

Figure 1: Without stateless, user and system files become mixed on the filesystem over time.

Clear Linux* OS has a stateless design philosophy of which the goal is to provide an OS that functions without excessive user configuration or customization. Stateless in this context does not mean ephemeral or non-persistent.

File-level separation

To accomplish a stateless design the Linux Filesystem Hierarchy is separated between user-owned areas and Clear Linux OS-owned areas.

Stateless: User and system files separation

Figure 2: With stateless, user and system files are separated on the filesystem.

System areas

File under the /usr directory are managed by Clear Linux OS as system files. Files written under the /usr directory by users can get removed through system updates with swupd.This operating assumption allows Clear Linux OS to verify and maintain integrity of system files.

User areas

Files under the /etc/, /home, and /var directories are owned and managed by the user. A freshly installed Clear Linux OS system will only have a minimal set of files in the /etc/ directory and software installed by Clear Linux OS does not write to /etc. This operating assumption allows Clear Linux OS users to clearly identify the configuration that makes their system unique.

Software Configuration

With stateless separation, default software configurations are read in order from predefined source code, Clear Linux OS provided defaults, and user-provided configuration.

Default configurations

Software in Clear Linux OS provides default configuration values so that it is immediately functional, whenever it is appropriate to do so.

Clear Linux OS distributed software packages may be directly modified to include default configuration values or default configuration files may be provided by Clear Linux OS under /usr/share/defaults. These files can be referenced as templates for customization.

For example, the default configuration that Apache uses when installed can be found at /usr/share/defaults/httpd/httpd.conf directory.

Overriding configurations

If a configuration needs to be changed, the appropriate file should be modified by the user under /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:

  1. Create the destination directory for the configuration:

    sudo mkdir /etc/httpd
    
  2. Copy the default configuration as a reference template:

    sudo cp /usr/share/defaults/httpd/httpd.conf /etc/httpd/
    
  3. Make any desired modifications to the configurations:

    sudoedit /etc/httpd/httpd.conf
    
  4. 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.

System reset

Once advantage of the stateless design is that the system defaults can be easily restored by simply deleting everything under /etc/ and /var.

Running the commands below effectively performs a system reset as if it was just installed:

sudo rm -rf /etc
sudo rm -rf /var

In other Linux distributions, this can be a catastrophic action that renders a system unable to boot.