Installation and Setup Quick Start
SUSE Linux Enterprise High Availability 15 SP4

# Installation and Setup Quick Start #

Publication Date: December 18, 2025

This document guides you through the setup of a very basic two-node cluster, using the bootstrap scripts provided by the CRM Shell. This includes the configuration of a virtual IP address as a cluster resource and the use of SBD on shared storage as a node fencing mechanism.

Revision History: Installation and Setup Quick Start

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## 1 Usage scenario #

The procedures in this document will lead to a minimal setup of a two-node cluster with the following properties:

- Two nodes: `alice` (IP: `192.168.1.1`) and `bob` (IP: `192.168.1.2`), connected to each other via network.

- A floating, virtual IP address (`192.168.1.10`) that allows clients to connect to the service no matter which node it is running on. This IP address is used to connect to the graphical management tool Hawk2.

- A shared storage device, used as SBD fencing mechanism. This avoids split-brain scenarios.

- Failover of resources from one node to the other if the active host breaks down (active/passive setup).

You can use the two-node cluster for testing purposes or as a minimal cluster configuration that you can extend later on. Before using the cluster in a production environment, see Book “Administration Guide” to modify the cluster according to your requirements.

## 2 System requirements #

This section informs you about the key system requirements for the scenario described in Section 1. To adjust the cluster for use in a production environment, refer to the full list in Book “Administration Guide”, Chapter 2 “System requirements and recommendations”.

### 2.1 Hardware requirements #

Servers

  Two servers with software as specified in Section 2.2, “Software requirements”.

  The servers can be bare metal or virtual machines. They do not require identical hardware (memory, disk space, etc.), but they must have the same architecture. Cross-platform clusters are not supported.

Communication channels

  At least two TCP/IP communication media per cluster node. The network equipment must support the communication means you want to use for cluster communication: multicast or unicast. The communication media should support a data rate of 100 Mbit/s or higher. For a supported cluster setup two or more redundant communication paths are required. This can be done via:

  - Network Device Bonding (preferred).

  - A second communication channel in Corosync.

Node fencing/STONITH

  A node fencing (STONITH) device to avoid split-brain scenarios. This can be either a physical device (a power switch) or a mechanism like SBD (STONITH by disk) in combination with a watchdog. SBD can be used either with shared storage or in diskless mode. This document describes using SBD with shared storage. The following requirements must be met:

  - A shared storage device. For information on setting up shared storage, see Storage Administration Guide for SUSE Linux Enterprise Server. If you only need basic shared storage for testing purposes, see Appendix A, Basic iSCSI storage for SBD.

  - The path to the shared storage device must be persistent and consistent across all nodes in the cluster. Use stable device names such as `/dev/disk/by-id/dm-uuid-part1-mpath-abcedf12345`.

  - The SBD device must not use host-based RAID, LVM, or DRBD*.

  For more information on STONITH, see Book “Administration Guide”, Chapter 12 “Fencing and STONITH”. For more information on SBD, see Book “Administration Guide”, Chapter 13 “Storage protection and SBD”.

### 2.2 Software requirements #

All nodes that will be part of the cluster need at least the following modules and extensions:

- Basesystem Module 15 SP4

- Server Applications Module 15 SP4

- SUSE Linux Enterprise High Availability 15 SP4

### 2.3 Other requirements and recommendations #

Time synchronization

  Cluster nodes must synchronize to an NTP server outside the cluster. Since SUSE Linux Enterprise High Availability 15, chrony is the default implementation of NTP. For more information, see the Administration Guide for SUSE Linux Enterprise Server 15 SP4.

  The cluster might not work properly if the nodes are not synchronized, or even if they are synchronized but have different timezones configured. In addition, log files and cluster reports are very hard to analyze without synchronization. If you use the bootstrap scripts, you will be warned if NTP is not configured yet.

Host name and IP address

  - Use static IP addresses.

  - Only the primary IP address is supported.

  - List all cluster nodes in the `/etc/hosts` file with their fully qualified host name and short host name. It is essential that members of the cluster can find each other by name. If the names are not available, internal cluster communication will fail.

SSH

  All cluster nodes must be able to access each other via SSH. Tools like `crm report` (for troubleshooting) and Hawk2's History Explorer require passwordless SSH access between the nodes, otherwise they can only collect data from the current node.

  If you use the bootstrap scripts for setting up the cluster, the SSH keys will automatically be created and copied.

## 3 Overview of the bootstrap scripts #

The following commands execute bootstrap scripts that require only a minimum of time and manual intervention.

- With `crm cluster init`, define the basic parameters needed for cluster communication. This leaves you with a running one-node cluster.

- With `crm cluster join`, add more nodes to your cluster.

- With `crm cluster remove`, remove nodes from your cluster.

The options set by the bootstrap scripts might not be the same as the Pacemaker default settings. You can check which settings the bootstrap scripts changed in `/var/log/crmsh/crmsh.log`. Any options set during the bootstrap process can be modified later with the YaST cluster module. See Book “Administration Guide”, Chapter 4 “Using the YaST cluster module” for details.

The bootstrap script `crm cluster init` checks and configures the following components:

NTP

  Checks if NTP is configured to start at boot time. If not, a message appears.

SSH

  Creates SSH keys for passwordless login between cluster nodes.

Csync2

  Configures Csync2 to replicate configuration files across all nodes in a cluster.

Corosync

  Configures the cluster communication system.

SBD/watchdog

  Checks if a watchdog exists and asks you whether to configure SBD as node fencing mechanism.

Virtual floating IP

  Asks you whether to configure a virtual IP address for cluster administration with Hawk2.

Firewall

  Opens the ports in the firewall that are needed for cluster communication.

Cluster name

  Defines a name for the cluster, by default `hacluster`. This is optional and mostly useful for Geo clusters. Usually, the cluster name reflects the geographical location and makes it easier to distinguish a site inside a Geo cluster.

QDevice/QNetd

  Asks you whether to configure QDevice/QNetd to participate in quorum decisions. We recommend using QDevice and QNetd for clusters with an even number of nodes, and especially for two-node clusters.

  This configuration is not covered here, but you can set it up later as described in Book “Administration Guide”, Chapter 14 “QDevice and QNetd”.

Note: Cluster configuration for different platforms

The `crm cluster init` script detects the system environment (for example, Microsoft Azure) and adjusts certain cluster settings based on the profile for that environment. For more information, see the file `/etc/crm/profiles.yml`.

## 4 Installing the High Availability packages #

The packages for configuring and managing a cluster are included in the `High Availability` installation pattern. This pattern is only available after the SUSE Linux Enterprise High Availability is installed.

You can register to the SUSE Customer Center and install SUSE Linux Enterprise High Availability while installing SUSE Linux Enterprise Server, or after installation. For more information, see the Deployment Guide for SUSE Linux Enterprise Server.

Procedure 1: Installing the High Availability pattern #

1. Install the High Availability pattern from the command line:

       # zypper install -t pattern ha_sles

2. Install the High Availability pattern on all machines that will be part of your cluster.

   Note: Installing software packages on all nodes

   For an automated installation of SUSE Linux Enterprise Server 15 SP4 and SUSE Linux Enterprise High Availability 15 SP4, use AutoYaST to clone existing nodes. For more information, see Book “Administration Guide”, Chapter 3 “Installing SUSE Linux Enterprise High Availability”, Section 3.2 “Mass installation and deployment with AutoYaST”.

## 5 Using SBD for node fencing #

Before you can configure SBD with the bootstrap script, you must enable a watchdog on each node. SUSE Linux Enterprise Server ships with several kernel modules that provide hardware-specific watchdog drivers. SUSE Linux Enterprise High Availability uses the SBD daemon as the software component that “feeds” the watchdog.

The following procedure uses the `softdog` watchdog.

Important: Softdog Limitations

The softdog driver assumes that at least one CPU is still running. If all CPUs are stuck, the code in the softdog driver that should reboot the system will never be executed. In contrast, hardware watchdogs keep working even if all CPUs are stuck.

Before using the cluster in a production environment, we highly recommend replacing the `softdog` module with the hardware module that best fits your hardware.

However, if no watchdog matches your hardware, `softdog` can be used as kernel watchdog module.

Procedure 2: Enabling the softdog watchdog for SBD #

1. On each node, enable the softdog watchdog:

       # echo softdog > /etc/modules-load.d/watchdog.conf
       # systemctl restart systemd-modules-load

2. Test if the softdog module is loaded correctly:

       # lsmod | grep dog
       softdog           16384  1

## 6 Setting up the first node #

Set up the first node with the `crm cluster init` script. This requires only a minimum of time and manual intervention.

Procedure 3: Setting up the first node (`alice`) with `crm cluster init` #

1. Log in as `root` to the physical or virtual machine to use as cluster node.

2. Start the bootstrap script:

       # crm cluster init --name CLUSTERNAME

   Replace the CLUSTERNAME placeholder with a meaningful name, like the geographical location of your cluster (for example, `amsterdam`). This is especially helpful to create a Geo cluster later on, as it simplifies the identification of a site.

   If you need to use multicast instead of unicast (the default) for your cluster communication, use the option `--multicast` (or `-U`).

   The script checks for NTP configuration and a hardware watchdog service. It generates the public and private SSH keys used for SSH access and Csync2 synchronization and starts the respective services.

3. Configure the cluster communication layer (Corosync):

   1. Enter a network address to bind to. By default, the script will propose the network address of `eth0`. Alternatively, enter a different network address, for example the address of `bond0`.

   2. Accept the proposed port (`5405`) or enter a different one.

4. Set up SBD as the node fencing mechanism:

   1. Confirm with `y` that you want to use SBD.

   2. Enter a persistent path to the partition of your block device that you want to use for SBD. The path must be consistent across all nodes in the cluster.

5. Configure a virtual IP address for cluster administration with Hawk2:

   1. Confirm with `y` that you want to configure a virtual IP address.

   2. Enter an unused IP address that you want to use as administration IP for Hawk2: `192.168.1.10`

      Instead of logging in to an individual cluster node with Hawk2, you can connect to the virtual IP address.

6. Choose whether to configure QDevice and QNetd. For the minimal setup described in this document, decline with `n` for now. You can set up QDevice and QNetd later, as described in Book “Administration Guide”, Chapter 14 “QDevice and QNetd”.

Finally, the script will start the cluster services to bring the cluster online and enable Hawk2. The URL to use for Hawk2 is displayed on the screen.

You now have a running one-node cluster. To view its status, proceed as follows:

Procedure 4: Logging in to the Hawk2 Web interface #

1. On any machine, start a Web browser and make sure that JavaScript and cookies are enabled.

2. As URL, enter the virtual IP address that you configured with the bootstrap script:

       https://192.168.1.10:7630/

   Note: Certificate warning

   If a certificate warning appears when you try to access the URL for the first time, a self-signed certificate is in use. Self-signed certificates are not considered trustworthy by default.

   Ask your cluster operator for the certificate details to verify the certificate.

   To proceed anyway, you can add an exception in the browser to bypass the warning.

3. On the Hawk2 login screen, enter the Username and Password of the user that was created by the bootstrap script (user `hacluster`, password `linux`).

   Important: Secure password

   Replace the default password with a secure one as soon as possible:

       # passwd hacluster

4. Click Log In. The Hawk2 Web interface shows the Status screen by default:

   Figure 1: Status of the one-node cluster in Hawk2 #

## 7 Adding the second node #

Add a second node to the cluster with the `crm cluster join` bootstrap script. The script only needs access to an existing cluster node and will complete the basic setup on the current machine automatically.

For more information, see the `crm cluster join --help` command.

Procedure 5: Adding the second node (`bob`) with `crm cluster join` #

1. Log in as `root` to the physical or virtual machine you want to add to the cluster.

2. Start the bootstrap script:

       # crm cluster join

   If NTP has not been configured to start at boot time, a message appears. The script also checks for a hardware watchdog device. You are warned if none is present.

3. If you decide to continue anyway, you will be prompted for the IP address of an existing node. Enter the IP address of the first node (`alice`, `192.168.1.1`).

4. If you have not already configured passwordless SSH access between both machines, you will be prompted for the `root` password of the existing node.

   After logging in to the specified node, the script will copy the Corosync configuration, configure SSH and Csync2, bring the current machine online as new cluster node, and start the service needed for Hawk2.

Check the cluster status in Hawk2. Under Status › Nodes you should see two nodes with a green status:

Figure 2: Status of the two-node cluster #

## 8 Testing the cluster #

The following tests can help you identify issues with the cluster setup. However, a realistic test involves specific use cases and scenarios. Before using the cluster in a production environment, test it thoroughly according to your use cases.

- The command `sbd -d DEVICE_NAME list` lists all of the nodes that are visible to SBD. For the setup described in this document, the output should show both `alice` and `bob`.

- Section 8.1, “Testing resource failover” is a simple test to check if the cluster moves the virtual IP address to the other node if the node that currently runs the resource is set to `standby`.

- Section 8.2, “Testing with the `crm cluster crash_test` command” simulates cluster failures and reports the results.

### 8.1 Testing resource failover #

As a quick test, the following procedure checks on resource failovers:

Procedure 6: Testing resource failover #

1. Open a terminal and ping `192.168.1.10`, your virtual IP address:

       # ping 192.168.1.10

2. Log in to Hawk2.

3. Under Status › Resources, check which node the virtual IP address (resource `admin-ip`) is running on. This procedure assumes the resource is running on `alice`.

4. Put `alice` into Standby mode:

   Figure 3: Node `alice` in standby mode #

5. Click Status › Resources. The resource `admin-ip` has been migrated to `bob`.

During the migration, you should see an uninterrupted flow of pings to the virtual IP address. This shows that the cluster setup and the floating IP work correctly. Cancel the `ping` command with Ctrl–C.

### 8.2 Testing with the `crm cluster crash_test` command #

The command `crm cluster crash_test` triggers cluster failures to find problems. Before you use your cluster in production, it is recommended to use this command to make sure everything works as expected.

The command supports the following checks:

`--split-brain-iptables`

  Simulates a split-brain scenario by blocking the Corosync port. Checks whether one node can be fenced as expected.

`--kill-sbd`/`--kill-corosync`/ `--kill-pacemakerd`

  Kills the daemons for SBD, Corosync, and Pacemaker. After running one of these tests, you can find a report in the directory `/var/lib/crmsh/crash_test/`. The report includes a test case description, action logging, and an explanation of possible results.

`--fence-node NODE`

  Fences a specific node passed from the command line.

For more information, see `crm cluster crash_test --help`.

Example 1: Testing the cluster: node fencing #

    # crm_mon -1
    Stack: corosync
    Current DC: alice (version ...) - partition with quorum
    Last updated: Fri Mar 03 14:40:21 2020
    Last change: Fri Mar 03 14:35:07 2020 by root via cibadmin on alice

    2 nodes configured
    1 resource configured

    Online: [ alice bob ]
    Active resources:

     stonith-sbd    (stonith:external/sbd): Started alice

    # crm cluster crash_test --fence-node bob

    ==============================================
    Testcase:          Fence node bob
    Fence action:      reboot
    Fence timeout:     60

    !!! WARNING WARNING WARNING !!!
    THIS CASE MAY LEAD TO NODE BE FENCED.
    TYPE Yes TO CONTINUE, OTHER INPUTS WILL CANCEL THIS CASE [Yes/No](No): Yes
    INFO: Trying to fence node "bob"
    INFO: Waiting 60s for node "bob" reboot...
    INFO: Node "bob" will be fenced by "alice"!
    INFO: Node "bob" was successfully fenced by "alice"

To watch `bob` change status during the test, log in to Hawk2 and navigate to Status › Nodes.

## 9 Next steps #

The bootstrap scripts provide a quick way to set up a basic High Availability cluster that can be used for testing purposes. However, to expand this cluster into a functioning High Availability cluster that can be used in production environments, more steps are recommended.

Recommended steps to complete the High Availability cluster setup #

Adding more nodes

  Add more nodes to the cluster using one of the following methods:

  - For individual nodes, use the `crm cluster join` script as described in Section 7, “Adding the second node”.

  - For mass installation of multiple nodes, use AutoYaST as described in Book “Administration Guide”, Chapter 3 “Installing SUSE Linux Enterprise High Availability”, Section 3.2 “Mass installation and deployment with AutoYaST”.

  A regular cluster can contain up to 32 nodes. With the `pacemaker_remote` service, High Availability clusters can be extended to include additional nodes beyond this limit. See Article “Pacemaker Remote Quick Start” for more details.

Enabling a hardware watchdog

  Before using the cluster in a production environment, replace the `softdog` module with the hardware module that best fits your hardware. For details, see Book “Administration Guide”, Chapter 13 “Storage protection and SBD”, Section 13.6 “Setting up the watchdog”.

Adding more STONITH devices

  For critical workloads, we highly recommend using two or three STONITH devices:

  - To continue using SBD, see Book “Administration Guide”, Chapter 13 “Storage protection and SBD”.

  - To use physical STONITH devices instead, see Book “Administration Guide”, Chapter 12 “Fencing and STONITH”.

Configuring QDevice

  If the cluster has an even number of nodes, configure QDevice and QNetd to participate in quorum decisions. QDevice provides a configurable number of votes, allowing a cluster to sustain more node failures than the standard quorum rules allow. For details, see Book “Administration Guide”, Chapter 14 “QDevice and QNetd”.

## 10 For more information #

More documentation for this product is available at https://documentation.suse.com/sle-ha/15-SP4/. For further configuration and administration tasks, see the comprehensive Administration Guide.

# A Basic iSCSI storage for SBD #

Revision History: Installation and Setup Quick Start

Use the following procedures to configure basic iSCSI storage to use with SBD. These procedures are only recommended for testing purposes. Before using iSCSI in a production environment, see Storage Administration Guide for SUSE Linux Enterprise Server.

Requirements #

- A SUSE Linux Enterprise Server virtual machine to act as the iSCSI target. This VM is not part of the cluster.

- Two virtual storage devices on the VM: a 20 GB device for the system, and a 1 GB device for SBD.

- Two SUSE Linux Enterprise Server nodes that have not been added to a High Availability cluster yet.

First, set up an iSCSI target on the virtual machine:

Procedure A.1: Configuring an iSCSI target #

1. Install the package yast2-iscsi-lio-server:

       # zypper install yast2-iscsi-lio-server

2. Start the `iscsi-lio-server` module in YaST:

       # yast2 iscsi-lio-server

3. In the Service tab, under After reboot, select Start on boot.

4. Activate Open Port in Firewall.

5. In the Global tab, activate Discovery Authentication.

6. Under Authentication by Targets, enter a Username and Password.

7. Under Authentication by Initiators, enter a Mutual Username and Mutual Password. This password must be different from the Authentication by Targets password.

8. In the Targets tab, select Add.

9. Change the Target name by replacing `.com.example`.

10. The IP Address of this server should be filled automatically. If not, add the IP address now.

11. Select Add.

12. In the LUN Details window, enter the LUN Path to the 1 GB storage device (for example, `/dev/vbd`).

13. Select Ok.

14. Select Next.

15. Select Finish to close YaST.

16. To check the target setup, switch to the target CLI:

        # targetcli

    Show the configuration:

        /> ls

Next, set up iSCSI initiators on the nodes. Repeat this procedure on both nodes:

Procedure A.2: Configuring an iSCSI initiator #

1. Install the required packages:

       # zypper install open-iscsi yast2-iscsi-client

2. Start the `iscsid` service:

       # systemctl start iscsid

3. Open the `iscsi-client` module in YaST:

       # yast2 iscsi-client

4. In the Discovered Targets tab, select Discovery.

5. Enter the IP address of the iSCSI target.

6. Clear No Discovery Authentication.

7. Under Authentication by Initiator, enter the initiator Username and Password.

8. Under Authentication by Targets, enter the target Username and Password.

9. Select Next.

10. After YaST discovers the iSCSI target, select Connect.

11. Under Startup, select onboot.

12. Select Next.

13. Select Ok to close YaST.

14. Check the iSCSI initiator:

        # lsscsi
        [0:0:1:0] cd/dvd QEMU QEMU DVD-ROM 2.5+ /dev/sr0
        [2:0:0:0] disk LIO-ORG IBLOCK 4.0 /dev/sda

    Look for a line with `IBLOCK`. In this example, the iSCSI device is `/dev/sda`.

15. Check the status of the `iscsid` service:

        # systemctl status iscsid

You can find the stable device name in `/dev/disk/by-id/`. Usually, an iSCSI device starts with `scsi-SLIO-ORG_IBLOCK`.

If you have multiple disks, you can run the command `lsblk -o name,serial` to confirm which stable device name corresponds to which short name (for example, `/dev/sda`).

When you configure the cluster, specify the stable device name using one of these methods:

- When you run `crm cluster init`, enter the stable device name when prompted.

- Before running `crm cluster init`, add the stable device name to `/etc/sysconfig/sbd`:

      SBD_DEVICE=/dev/disk/by-id/scsi-SLIO-ORG_IBLOCK_DEVICE_ID_STRING

  When you run `crm cluster init`, answer `n` for this question:

      SBD is already configured to use /dev/disk/by-id/scsi-SLIO-ORG_IBLOCK_... - overwrite (y/n)?

# B GNU licenses #

Revision History: Installation and Setup Quick Start

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Revision History: Installation and Setup Quick Start

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If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

##### 4. MODIFICATIONS #

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

4. Preserve all the copyright notices of the Document.

5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

8. Include an unaltered copy of this License.

9. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

11. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

##### 5. COMBINING DOCUMENTS #

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

##### 6. COLLECTIONS OF DOCUMENTS #

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

##### 7. AGGREGATION WITH INDEPENDENT WORKS #

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

##### 8. TRANSLATION #

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

##### 9. TERMINATION #

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

##### 10. FUTURE REVISIONS OF THIS LICENSE #

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

##### ADDENDUM: How to use this License for your documents #

    Copyright (c) YEAR YOUR NAME.
    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.2
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
    A copy of the license is included in the section entitled “GNU
    Free Documentation License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.