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Customizing installation

  1. Creating customized ISO and PXE images
    1. Customize options
  2. Customizing coreos-installer invocation
    1. Config file format
    2. Example manual customization via installer.d

Creating customized ISO and PXE images

The iso customize and pxe customize commands can be used to create customized ISO and PXE images with site-specific configuration, including the ability to perform unattended installations. This is the recommended method for automatically running coreos-installer at boot.

For example:

# Create customized.iso which:
# - Automatically installs to /dev/sda
# - Provisions the installed system with config.ign
# - Uses network configuration from static-ip.nmconnection
# - Trusts HTTPS certificates signed by ca.pem
# - Runs after installing
coreos-installer iso customize \
    --dest-device /dev/sda \
    --dest-ignition config.ign \
    --network-keyfile static-ip.nmconnection \
    --ignition-ca ca.pem \
    --post-install \
    -o custom.iso input.iso
# Same, but create a customized PXE initramfs image
coreos-installer pxe customize \
    --dest-device /dev/sda \
    --dest-ignition config.ign \
    --network-keyfile static-ip.nmconnection \
    --ignition-ca ca.pem \
    --post-install \
    -o custom-initramfs.img input-initramfs.img

Customize options

Available customizations include:

  • Specifying an Ignition config to be applied to the installed system (--dest-ignition) or to the live environment where the installer runs (--live-ignition).
  • Specifying the device to which the operating system will be installed (--dest-device). If an ISO or PXE image has been customized with --dest-device, booting that image will automatically install to the specified disk and reboot the system.
  • Specifying network configuration for both the installed system and the live environment via NetworkManager keyfiles (--network-keyfile). The configuration is applied before Ignition runs, so this option is useful for specifying network settings that are needed for Ignition to fetch remote resources.
  • Specifying HTTPS certificate authorities to be trusted by Ignition, in both the installed system and the live environment (--ignition-ca).
  • Modifying kernel arguments of the installed system (--dest-karg-append, --dest-karg-delete) or the live ISO environment (--live-karg-append, --live-karg-replace, --live-karg-delete). These options are useful if the machine will not boot at all without certain kernel arguments, preventing use of the Ignition kernel_arguments directives. There are no --live-karg options for the PXE image; modify the PXE boot configuration instead.
  • Running scripts before or after installation (--pre-install, --post-install). For example, a pre-install script might run a container that performs hardware validation, or a post-install script might use IPMI to configure the machine to boot from the local disk instead of the network. Pre-install scripts can change the options processed by coreos-installer, including the choice of destination device, by writing an installer config file to /etc/coreos/installer.d (see below).
  • Specifying arbitrary options to coreos-installer install via an installer config file (see below).

All options except --dest-device can be specified multiple times.

Customizing coreos-installer invocation

Alternatively, coreos-installer can be run automatically during boot of a CoreOS live image (ISO or PXE) using either kernel command-line arguments or a config file.

Kernel arguments are easier for simple cases, but not all coreos-installer parameters can be specified that way. For more complex cases, you can write one or more config files to /etc/coreos/installer.d. If any files exist in this directory, coreos-installer will automatically run on boot, and will reboot the live system after installation is complete.

To do this, specify an Ignition config to the live boot that runs the installer. This config is distinct from the Ignition config that governs the installed system.

All config files in the installer.d directory are evaluated in alphabetical order, and any coreos.inst kernel command line arguments are evaluated afterward.

Config file format

Config files in /etc/coreos/installer.d (or specified by --config-file) are YAML documents containing directives with the same names and semantics as command-line arguments. Each specified config file is parsed in order, and other command-line arguments are parsed afterward.

All parameters are optional.

# Fedora CoreOS stream
stream: name
# Manually specify the image URL
image-url: URL
# Manually specify a local image file
image-file: path
# Embed an Ignition config from a file
ignition-file: path
# Embed an Ignition config from a URL
ignition-url: URL
# Digest (type-value) of the Ignition config
ignition-hash: digest
# Override the Ignition platform ID
platform: name
# Append default kernel arguments
append-karg: [arg1, arg2]
# Delete default kernel arguments
delete-karg: [arg1, arg2]
# Copy network config from install environment
copy-network: true
# Source directory for copy-network
network-dir: path
# Save partitions with this label glob
save-partlabel: [glob, glob]
# Save partitions with this number or range
save-partindex: [id-or-range, id-or-range]
# Force offline installation
offline: true
# Skip signature verification
insecure: true
# Allow Ignition URL without HTTPS or hash
insecure-ignition: true
# Base URL for Fedora CoreOS stream metadata
stream-base-url: URL
# Target CPU architecture
architecture: name
# Don't clear partition table on error
preserve-on-error: true
# Fetch retries, or string "infinite"
fetch-retries: N
# Destination device
dest-device: path

Example manual customization via installer.d

This is an example procedure for configuring an ISO or PXE installation to /dev/zda using an installer config file. The ISO procedure matches the steps performed by coreos-installer iso customize --dest-device, and the PXE procedure produces the same result as coreos-installer pxe customize --dest-device via a slightly different path.

Write a Butane config that installs to /dev/zda:

variant: fcos
version: 1.4.0
    - path: /etc/coreos/installer.d/custom.yaml
        inline: |
          dest-device: /dev/zda

Convert this Butane config to an Ignition config with:

butane < install.bu > install.ign

For live ISO booting, embed the resulting config in the live ISO:

coreos-installer iso ignition embed -i install.ign fedora-coreos-35.20211029.3.0-live.x86_64.iso

For live PXE booting, use only the Ignition first-boot arguments in the kernel argument list:

ignition.config.url= ignition.firstboot