Tutorial: Install Clear Linux* OS over the network with iPXE

This guide describes how to install Clear Linux* OS using PXE.

PXE is an industry standard that describes client-server interaction with network-boot software and uses the DHCP and TFTP protocols. This guide shows one method of using the PXE environment to install Clear Linux OS.

The PXE extension called iPXE adds support for additional protocols such as HTTP, iSCSI, AoE, and FCoE. iPXE enables network booting on computers with no built-in PXE support.

To install Clear Linux OS through iPXE, you must create a PXE client. Figure 1 depicts the flow of information between a PXE server and a PXE client.

PXE information flow

Figure 1: PXE information flow.

Caution

The Clear Linux OS image that boots through the PXE process automatically erases all data and partitions on the PXE client system and creates 3 new partitions to install onto.

Prerequisites

Before booting with iPXE, make the following preparations.

Connect the PXE server and PXE clients to a switch on a private network, as shown in Figure 2.

Network topology

Figure 2: Network topology.

Your PXE client must have a boot order where the network boot option is prioritized before the disk boot option.

Your PXE server must have:

  • Ethernet/LAN boot option.
  • At least two network adapters.
  • Connection to a public network.
  • Secure boot option disabled.

Note

You must disable the secure boot option in the BIOS because the UEFI binaries used to boot Clear Linux OS are not signed.

Configuration

To set up Clear Linux OS using iPXE automatically, use the configure-ipxe.sh script included with ICIS. For additional instructions on the script, refer to the guide on the ICIS GitHub repository .

To set up Clear Linux OS manually, perform the steps below.

  1. Define the variables used for iPXE boot configuration.

ipxe_app_name=ipxe ipxe_port=50000 web_root=/var/www ipxe_root=$web_root/$ipxe_app_name tftp_root=/srv/tftp external_iface=eno1 internal_iface=eno2 pxe_subnet=192.168.1 pxe_internal_ip=$pxe_subnet.1 pxe_subnet_mask_ip=255.255.255.0 pxe_subnet_bitmask=16

  1. Log in and get root privilege.

sudo -s

  1. Add the pxe-server bundle to your Clear Linux OS system. The bundle contains all files needed to run a PXE server.

sudo swupd bundle-add pxe-server

  1. Download the latest network-bootable release of Clear Linux OS and extract the files.

sudo mkdir -p $ipxe_root sudo curl -o /tmp/clear-pxe.tar.xz \ https://download.clearlinux.org/current/clear-$(curl \ https://download.clearlinux.org/latest)-pxe.tar.xz sudo tar -xJf /tmp/clear-pxe.tar.xz -C $ipxe_root sudo ln -sf $(ls $ipxe_root | grep 'org.clearlinux.*') $ipxe_root/linux

Note

Ensure that the initial ramdisk file is named initrd and the kernel file is named linux, which is a symbolic link to the actual kernel file.

  1. Create an iPXE boot script with the following contents. During an iPXE boot, the iPXE boot script directs the PXE client to download the files to boot and install Clear Linux OS. Use the names previously given to the initial ramdisk and kernel files.

sudo cat > $ipxe_root/ipxe_boot_script.ipxe << EOF #!ipxe kernel linux quiet init=/usr/lib/systemd/systemd-bootchart \ initcall_debug tsc=reliable no_timer_check noreplace-smp rw \ initrd=initrd initrd initrd boot EOF

  1. The pxe-server bundle contains a lightweight web-server known as nginx. Create a configuration file for nginx to serve Clear Linux OS to PXE clients with the following contents:

sudo mkdir -p /etc/nginx/conf.d sudo cat > /etc/nginx/conf.d/$ipxe_app_name.conf << EOF server { listen $ipxe_port; server_name localhost; location /$ipxe_app_name/ { root $web_root; autoindex on; } } EOF sudo cp /usr/share/nginx/conf/nginx.conf.example /etc/nginx/nginx.conf

Note

Create a separate nginx configuration file to serve network-bootable images on a non-standard port number. This action saves existing nginx configurations.

  1. Start nginx and enable the startup on boot option.

sudo systemctl start nginx sudo systemctl enable nginx

  1. The pxe-server bundle contains a lightweight DNS server which conflicts with the DNS stub listener provided in systemd-resolved. Disable the DNS stub listener and temporarily stop systemd-resolved.

sudo mkdir -p /etc/systemd sudo cat > /etc/systemd/resolved.conf << EOF [Resolve] DNSStubListener=no EOF sudo systemctl stop systemd-resolved

  1. Assign a static IP address to the network adapter for the private network and restart systemd-networkd with the following commands:

sudo mkdir -p /etc/systemd/network sudo cat > /etc/systemd/network/70-internal-static.network << EOF [Match] Name=$internal_iface [Network] DHCP=no Address=$pxe_internal_ip/$pxe_subnet_bitmask EOF sudo systemctl restart systemd-networkd

  1. Configure NAT to route traffic from the private network to the public network. This action makes the PXE server act as a router. To make these changes persistent during reboots, save the changes to the firewall with the following commands:

sudo iptables -t nat -F POSTROUTING sudo iptables -t nat -A POSTROUTING -o $external_iface -j MASQUERADE sudo systemctl enable iptables-save.service sudo systemctl restart iptables-save.service sudo systemctl enable iptables-restore.service sudo systemctl restart iptables-restore.service

Note

The firewall masks packets to make them appear as coming from the PXE server and hides PXE clients from the public network.

  1. Configure the kernel to forward network packets to different interfaces. Otherwise, NAT will not work.

sudo mkdir -p /etc/sysctl.d sudo echo net.ipv4.ip_forward=1 > /etc/sysctl.d/80-nat-forwarding.conf sudo echo 1 > /proc/sys/net/ipv4/ip_forward

  1. The pxe-server bundle contains iPXE firmware images that allow computers without an iPXE implementation to perform an iPXE boot. Create a TFTP hosting directory and populate the directory with the iPXE firmware images with the following commands:

sudo mkdir -p $tftp_root sudo ln -sf /usr/share/ipxe/undionly.kpxe $tftp_root/undionly.kpxe

  1. The pxe-server bundle contains a lightweight TFTP, DNS, and DHCP server known as dnsmasq. Create a configuration file for dnsmasq to listen on a dedicated IP address for those functions. PXE clients on the private network will use this IP address.

sudo cat > /etc/dnsmasq.conf << EOF listen-address=$pxe_internal_ip EOF

  1. Add the options to serve iPXE firmware images to PXE clients over TFTP to the dnsmasq configuration file.

sudo cat >> /etc/dnsmasq.conf << EOF enable-tftp tftp-root=$tftp_root EOF

  1. Add the options to host a DHCP server for PXE clients to the dnsmasq configuration file.

sudo cat >> /etc/dnsmasq.conf << EOF dhcp-leasefile=/var/db/dnsmasq.leases dhcp-authoritative dhcp-option=option:router,$pxe_internal_ip dhcp-option=option:dns-server,$pxe_internal_ip dhcp-match=set:pxeclient,60,PXEClient* dhcp-range=tag:pxeclient,$pxe_subnet.2,$pxe_subnet.253,$pxe_subnet_mask_ip,15m dhcp-range=tag:!pxeclient,$pxe_subnet.2,$pxe_subnet.253,$pxe_subnet_mask_ip,6h dhcp-match=set:ipxeboot,175 dhcp-boot=tag:ipxeboot,http://$pxe_internal_ip:$ipxe_port/$ipxe_app_name/ipxe_boot_script.ipxe dhcp-boot=tag:!ipxeboot,undionly.kpxe,$pxe_internal_ip EOF

The configuration provides the following important functions:

  • Directs PXE clients without an iPXE implementation to the TFTP server to acquire architecture-specific iPXE firmware images that allow them to perform an iPXE boot.
  • Activates only on the network adapter that has an IP address on the defined subnet.
  • Directs PXE clients to the DNS server.
  • Directs PXE clients to the PXE server for routing via NAT.
  • Divides the private network into two pools of IP addresses. One pool is for network boot and one pool is used after boot. Each pool has their own lease times.
  1. Create a file for dnsmasq to record the IP addresses it provides to PXE clients.

sudo mkdir -p /var/db sudo touch /var/db/dnsmasq.leases

  1. Start dnsmasq and enable startup on boot.

sudo systemctl enable dnsmasq sudo systemctl restart dnsmasq

  1. Start systemd-resolved.

sudo systemctl start systemd-resolved

Note

systemd-resolved dynamically updates the list of DNS servers for the private network if you use the dnsmasq DNS server. The setup creates a pass-through DNS server that relies on the DNS servers listed in /etc/resolv.conf.

  1. Power on the PXE client and watch the client boot and install Clear Linux OS.After booting, Clear Linux OS automatically partitions the hard drive, installs itself, updates to the latest version, and reboots.

Congratulations! You have successfully installed and configured a PXE server that enables PXE clients to boot and install Clear Linux OS over the network.

This tutorial was originally published here.

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