8 Configuring with Combustion #

Combustion is a dracut module that enables you to configure your system on its first boot. Combustion reads a provided file, called script and executes commands in it and thus perform changes to the file system. You can use Combustion to change the default partitions, set users' passwords, create files, install packages, etc.

The Combustion dracut module is invoked after the ignition.firstboot argument is passed to the kernel command line. Combustion then reads configuration from script. Combustion tries to configure network, if the network flag has been found in script. After /sysroot is mounted, Combustion tries to activate all mount points in /etc/fstab and then call transactional-update to apply other changes (like setting root password or installing packages).

When using Combustion, you need to label the configuration device with the name combustion, create a specific directory structure in that configuration medium, and include a configuration file named script. In the root directory of the configuration medium, create a directory called combustion and place the script into this directory along with other files—SSH key, configuration files, etc. The directory structure then should look as follows:

<root directory>
└── combustion
    └── script
    └── other files

You can use Combustion to configure your QEMU/KVM virtual machine. In this case, pass the location of the script file using the fw_cfg parameter of the qemu command:

	-fw_cfg name=opt/org.opensuse.combustion/script,file=/var/combustion-script

Combustion can be used along with Ignition. If you intend to do so, label your configuration medium ignition and include the ignition directory with the config.ign to your directory structure as shown below:

<root directory>
└── combustion
    └── script
    └── other files
└── ignition 
    └── config.ign

In this scenario, Ignition runs before Combustion.

The script configuration file is a set of commands that are executed on your system in a transactional-update shell. This section provides examples for performing various configuration tasks by using Combustion.

Important: Include interpreter declaration

As the script file is interpreted by shell, make sure to start the file with the interpreter declaration at the first line, for example for Bash:

 #!/bin/bash

If you want to log in to your system, include at least the root password. Though it is recommend to establish the authentication using SSH keys. If you need to use a root password, make sure to configure a secure password. In case you use a randomly generated password, use at least 10 characters. If you create your password manually, use even more than 10 characters and combine uppercase and lowercase letters, and numbers.

 # combustion: network

8.2.2 Partitioning #

  

SLE Micro raw images are delivered with a default partitioning scheme as described in Section 5.1, “Default partitioning”. You might want to use a different partitioning. The following set of example snippets moves the /home to a different partition.

Note: Performing changes outside of directories included in snapshots

The following script performs changes that are not included in snapshots. If the script fails and the snapshot get discarded, some changes remains visible and cannot be reverted (like the changes to the /dev/vdb device.)

The following snippet creates a GPT with a single partition on the /dev/vdb device:

sfdisk /dev/vdb <<EOF
label: gpt
type=linux
EOF 

partition=/dev/vdb1

As the sfdisk command may take longer time to complete, postpone label by using the sleep command after sfdisk.

The partition is formatted to BTRFS:

wipefs --all ${partition}
mkfs.btrfs ${partition}

Possible content of /home is moved to the new /home folder location by the following snippet:

mount /home
mount ${partition} /mnt 
rsync -aAXP /home/ /mnt/
umount /home /mnt

The snippet below removes an old entry in /etc/fstab and creates a new entry:

awk -i inplace '$2 != "/home"' /etc/fstab
echo "$(blkid -o export ${partition} | grep ^UUID=) /home btrfs defaults 0 0" >>/etc/fstab

 echo 'root:$5$.wn2BZHlEJ5R3B1C$TAHEchlU.h2tvfOpOki54NaHpGYKwdNhjaBuSpDotD7' | chpasswd -e

8.2.4 Adding SSH keys #

  

The following snippet creates a directory to store the root's SSH key and then copies the public SSH key located on the configuration device to the authorized_keys file.

 mkdir -pm700 /root/.ssh/
cat id_rsa_new.pub >> /root/.ssh/authorized_keys

Note

The SSH service must be enabled in case you need to use remote login via SSH. For details, refer to Section 8.2.5, “Enabling services”.

 systemctl enable sshd.service

8.2.6 Installing packages #

  

Important: Network connection and registering your system might be necessary

As some package may require additional subscription, you might need to register your system beforehand. Also available network connection may be needed to install additional packages.

During the first boot configuration, you can install additional packages to your system. For example, you can install the vim editor by adding:

zypper --non-interactive install vim-small

Note

Bear in mind that you will not be able to use zypper after the configuration is complete and you boot to the configured system. To perform changes later, you must use the transactional-update command to create a changed snapshot. For details, refer to Section 2, “Administration using transactional updates”.