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 "

Procedure

1. Enable the tftp service:

   # systemctl enable --now tftp

2. Create a pxelinux directory inside 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/

   • You can find the tftp root directory (chroot) in the /var/lib/tftpboot directory.

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 inside the tftp root directory:

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

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

Procedure

1. Add the 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.

Configuring a File System

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 file system (/exported-root-directory) 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

Procedure

1. To change the user password, follow the steps below:

   • Change the command line to /exported/root/directory:

     # chroot /exported/root/directory /bin/bash

   • Change the password for the user you want:

     # passwd <username>

     Replace the <username> with a real user to whom you want to change the password.

   • Exit the command line.

2. Install software on a remote diskless system:

   # dnf install <package> --installroot=/exported/root/directory --releasever=/ --config /etc/dnf/dnf.conf --setopt=reposdir=/etc/yum.repos.d/

   • Replace <package> with the actual package you want to install.
3. Configure two separate exports to split a remote diskless system into a /usr and a /var. See Deploying an NFS server.