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Kevin Putnam
140 lines
4.2 KiB
ReStructuredText
140 lines
4.2 KiB
ReStructuredText
.. _stateless:
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Stateless
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#########
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In most operating systems, user data, system data, and configuration files
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can become intermingled.
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.. figure:: figures/stateless-1.png
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:scale: 45%
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:align: center
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:alt: Stateless: User and system files mixed
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Figure 1: Without stateless, user and system files become mixed on the filesystem over time.
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|CL-ATTR| has a stateless design philosophy with the goal to provide an
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:abbr:`OS (operating system)` that functions without excessive user
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configuration or customization. Stateless in this context does *not* mean
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ephemeral or non-persistent.
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.. contents:: :local:
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:depth: 1
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File-level separation
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*********************
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To accomplish a stateless design the Linux Filesystem Hierarchy is separated
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between user-owned areas and |CL|-owned areas.
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.. figure:: figures/stateless-2.png
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:scale: 45%
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:align: center
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:alt: Stateless: User and system files separation
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Figure 2: With stateless, user and system files are separated on the filesystem.
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System areas
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============
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File under the :file:`/usr` directory are managed by |CL| as system files.
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Files written under the :file:`/usr` directory by users can get removed
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through system updates with :ref:`swupd <swupd-about>`.This operating
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assumption allows |CL| to verify and maintain integrity of system files.
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User areas
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==========
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Files under the :file:`/etc/`, :file:`/home`, and :file:`/var` directories are
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owned and managed by the user. A freshly installed |CL| system will only have
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a minimal set of files in the :file:`/etc/` directory and software installed
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by |CL| does not write to :file:`/etc`. This operating assumption allows |CL|
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users to clearly identify the configuration that makes their system unique.
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Software configuration
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**********************
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With stateless separation, default software configurations are read in order
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from predefined source code, |CL| provided defaults, and user-provided
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configuration.
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Default configurations
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======================
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Software in |CL| provides default configuration values so that it is
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immediately functional, whenever it is appropriate to do so.
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|CL| distributed software packages may be directly modified to include default
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configuration values or default configuration files may be provided by |CL|
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under :file:`/usr/share/defaults`. These files can be referenced as templates
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for customization.
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For example, the default configuration that Apache uses when installed can be
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found at :file:`/usr/share/defaults/httpd/httpd.conf` directory.
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Overriding configurations
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=========================
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If a configuration needs to be changed, the appropriate file should be
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modified by the user under :file:`/etc/`. If the configuration file does not
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already exist, it can be created in the appropriate location.
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User defined configuration files should contain the minimal set of desired
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changes and rely on default configuration for the rest.
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For example, a customized Apache configuration can be used instead by:
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#. Create the destination directory for the configuration:
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.. code-block:: bash
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sudo mkdir /etc/httpd
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#. Copy the default configuration as a reference template:
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.. code-block:: bash
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sudo cp /usr/share/defaults/httpd/httpd.conf /etc/httpd/
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#. Make any desired modifications to the configurations:
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.. code-block:: bash
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sudoedit /etc/httpd/httpd.conf
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#. Reload the service or reboot the system to pickup any changes:
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.. code-block:: bash
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systemctl daemon-reload httpd && systemctl restart httpd
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This pattern can be used to modify the configurations of other programs too.
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The `stateless man page`_ has application-specific examples.
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System reset
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************
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Once advantage of the stateless design is that the system defaults can be
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easily restored by simply deleting everything under :file:`/etc/` and
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:file:`/var`.
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Running the commands below effectively performs a system reset as if it was
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just installed:
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.. code-block:: bash
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sudo rm -rf /etc
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sudo rm -rf /var
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In other Linux distributions, this can be a catastrophic action that renders
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a system unable to boot.
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Additional information
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**********************
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* `stateless man page`_
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.. _`stateless man page`: https://github.com/clearlinux/clr-man-pages/blob/master/stateless.7.rst
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