Chapter 20. Setting up a remote diskless system

Procedure

1. Install the dracut-network package:

   # yum install dracut-network

2. After installing the dracut-network package, add the following line to /etc/dracut.conf:

   add_dracutmodules+="nfs"

To Configure tftp

1. Enable PXE booting over the network:

   # systemctl enable --now tftp

2. The tftp root directory (chroot) is located in /var/lib/tftpboot. Copy /usr/share/syslinux/pxelinux.0 to /var/lib/tftpboot/:

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

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

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

4. Create a pxelinux.cfg directory inside the tftp root directory:

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

5. After configuring tftp for diskless clients, configure DHCP, NFS, and the exported file system accordingly.

Procedure

1. Set up a DHCP server and enable PXE booting by adding the following configuration to /etc/dhcp/dhcpd.conf:

   allow booting;
   allow bootp;
   subnet 192.168.205.0 netmask 255.255.255.0 {
     pool
     {
       range 192.168.205.10 192.168.205.25;
     }
   
     option subnet-mask 255.255.255.0;
     option routers 192.168.205.1;
   }
   class "pxeclients" {
      match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
      next-server server-ip;
      filename "pxelinux.0";
   }

   This configuration will not boot over UEFI. To perform installation for UEFI, follow the procedure from this documentation: Configuring a TFTP server for UEFI-based clients. Also, note that the /etc/dhcp/dhcpd.conf is an example file.

   Note

   When libvirt virtual machines are used as a diskless client, libvirt provides the DHCP service and the stand alone 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 by entering the following command:

   # systemctl enable --now dhcpd.service

Procedure

1. Configure the NFS server to export the root directory by adding it to /etc/exports. For the instructions see NFS server configuration.

2. To accommodate completely diskless clients, the root directory should contain a complete Red Hat Enterprise Linux installation. You can either install a new base system or clone an existing installation:

   • To install Red Hat Enterprise Linux to the exported location, use the yum utility with the --installroot option:

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

   • To synchronize with a running system, use the rsync utility:

     # 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.

Configure File System

1. Select the kernel that diskless clients should use (vmlinuz-kernel-version) and copy it to the tftp boot directory:

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

2. Create the initrd that is, 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-4.18.0-348.20.1.el8_5.x86_64.img 4.18.0-348.20.1.el8_5.x86_64

3. Change file permissions for initrd to 644 using the following command:

   # chmod 644 /exported-root-directory/boot/initramfs-<kernel-version>.img

   Warning

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

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

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

5. Edit the default boot configuration to use the initrd and kernel in the /var/lib/tftpboot/ directory. This configuration should instruct the diskless client’s root to mount the exported file system (/exported-root-directory) as read-write. Add the following configuration in the /var/lib/tftpboot/pxelinux.cfg/default file:

   default rhel8
   
   label rhel8
     kernel vmlinuz-kernel-version
     append initrd=initramfs-kernel-version.img root=nfs:server-ip:/exported-root-directory rw

   Replace server-ip with the IP address of the host machine on which the tftp and DHCP services reside.

6. Optionally, you can mount the system in read-only format by using the following configuration in the /var/lib/tftpboot/pxelinux.cfg/default file:

   default rhel8
   
   label rhel8
     kernel vmlinuz-kernel-version
     append initrd=initramfs-kernel-version.img root=nfs:server-ip:/exported-root-directory ro

7. Reboot the NFS server.

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:

     # exit

2. To install software to a remote diskless system, use the following command:

   # yum 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. To split a remote diskless system into a /usr and a /var you must configure two separate exports. Read NFS server configuration documentation for details.