Chapter 15. Setting up a remote diskless system

Procedure

1. Install the dracut-network package:

   # dnf install dracut-network

2. Add the following line to the /etc/dracut.conf.d/network.conf file:

   add_dracutmodules+=" nfs "

3. Ensure correct functionality of the remote diskless system in your environment by configuring services in the following order:

   1. Configure a TFTP service. For more information, see Configuring a TFTP service for diskless clients.
   2. Configure a DHCP server. For more information, see Configuring a DHCP server for diskless clients.
   3. Configure the Network File System (NFS) and an exported file system. For more information, see Configuring an exported file system for diskless clients.

Procedure

1. Enable the tftp service:

   # systemctl enable --now tftp

2. Create a pxelinux directory in the tftp root directory:

   # mkdir -p /var/lib/tftpboot/pxelinux/

3. Copy the /usr/share/syslinux/pxelinux.0 file to the /var/lib/tftpboot/pxelinux/ directory:

   # cp /usr/share/syslinux/pxelinux.0 /var/lib/tftpboot/pxelinux/

4. Copy /usr/share/syslinux/ldlinux.c32 to /var/lib/tftpboot/pxelinux/:

   # cp /usr/share/syslinux/ldlinux.c32 /var/lib/tftpboot/pxelinux/

5. Create a pxelinux.cfg directory in the tftp root directory:

   # mkdir -p /var/lib/tftpboot/pxelinux/pxelinux.cfg/

   Note

   This configuration does not boot over the Unified Extensible Firmware Interface (UEFI). To perform the installation for UEFI, see Configuring a TFTP server for UEFI-based clients.

Procedure

1. Add the following configuration to the /etc/dhcp/dhcpd.conf file to setup a DHCP server and enable Preboot Execution Environment (PXE) for booting:

   option space pxelinux;
   option pxelinux.magic code 208 = string;
   option pxelinux.configfile code 209 = text;
   option pxelinux.pathprefix code 210 = text;
   option pxelinux.reboottime code 211 = unsigned integer 32;
   option architecture-type code 93 = unsigned integer 16;
   
   subnet 192.168.205.0 netmask 255.255.255.0 {
     option routers 192.168.205.1;
     range 192.168.205.10 192.168.205.25;
   
     class "pxeclients" {
       match if substring (option vendor-class-identifier, 0, 9) = "PXEClient";
       next-server 192.168.205.1;
   
       if option architecture-type = 00:07 {
         filename "BOOTX64.efi";
         } else {
         filename "pxelinux/pxelinux.0";
       }
     }
   }

   Your DHCP configuration might be different depending on your environment, like setting lease time or fixed address. For details, see Providing DHCP services.

   Note

   While using libvirt virtual machine as a diskless client, the libvirt daemon provides the DHCP service, and the standalone DHCP server is not used. In this situation, network booting must be enabled with the bootp file=<filename> option in the libvirt network configuration, virsh net-edit.

2. Enable dhcpd.service:

   # systemctl enable --now dhcpd.service

Procedure

1. Configure the Network File System (NFS) server to export the root directory by adding it to the /etc/exports directory. For the complete set of instructions see

   • Deploying an NFS server

2. Install a complete version of Red Hat Enterprise Linux to the root directory to accommodate completely diskless clients. To do that you can either install a new base system or clone an existing installation.

   • Install Red Hat Enterprise Linux to the exported location by replacing exported-root-directory with the path to the exported file system:

     # dnf install @Base kernel dracut-network nfs-utils --installroot=exported-root-directory --releasever=/

     By setting the releasever option to /, releasever is detected from the host (/) system.

   • Use the rsync utility to synchronize with a running system:

     # rsync -a -e ssh --exclude='/proc/' --exclude='/sys/' example.com:/ exported-root-directory

     • Replace example.com with the hostname of the running system with which to synchronize via the rsync utility.

     • Replace exported-root-directory with the path to the exported file system.

       Note, that for this option you must have a separate existing running system, which you will clone to the server by the command above.

3. Configure the file system, which is ready for export, before you can use it with diskless clients:

   1. Copy the diskless client supported kernel (vmlinuz-_kernel-version_pass:attributes) to the tftp boot directory:

      # cp /exported-root-directory/boot/vmlinuz-kernel-version /var/lib/tftpboot/pxelinux/

   2. Create the initramfs-kernel-version.img file locally and move it to the exported root directory with NFS support:

      # dracut --add nfs initramfs-kernel-version.img kernel-version

      For example:

      # dracut --add nfs /exports/root/boot/initramfs-5.14.0-202.el9.x86_64.img 5.14.0-202.el9.x86_64

      Example for creating initrd, using current running kernel version, and overwriting existing image:

      # dracut -f --add nfs "boot/initramfs-$(uname -r).img" "$(uname -r)"

   3. Change the file permissions for initrd to 0644:

      # chmod 0644 /exported-root-directory/boot/initramfs-kernel-version.img

      Warning

      If you do not change the initrd file permissions, the pxelinux.0 boot loader fails with a "file not found" error.

   4. Copy the resulting initramfs-kernel-version.img file into the tftp boot directory:

      # cp /exported-root-directory/boot/initramfs-kernel-version.img /var/lib/tftpboot/pxelinux/

   5. Add the following configuration in the /var/lib/tftpboot/pxelinux/pxelinux.cfg/default file to edit the default boot configuration for using the initrd and the kernel:

      default rhel9
      
      label rhel9
        kernel vmlinuz-kernel-version
        append initrd=initramfs-kernel-version.img root=nfs:_server-ip_:/exported-root-directory rw

      This configuration instructs the diskless client root to mount the /exported-root-directory exported file system in a read/write format.

   6. Optional: Mount the file system in a read-only` format by editing the /var/lib/tftpboot/pxelinux/pxelinux.cfg/default file with the following configuration:

      default rhel9
      
      label rhel9
        kernel vmlinuz-kernel-version
        append initrd=initramfs-kernel-version.img root=nfs:server-ip:/exported-root-directory ro

   7. Restart the NFS server:

      # systemctl restart nfs-server.service