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Virtual Media ISO Booting


The Virtual Media ISO mount and booting method is currently a Technical Preview, as of December 2020. This feature will be available in the v4.6.0 version (as a Tech Preview). The documentation in this guide may be out of sync with usage as this feature is productionized. Contact RackN support for any questions.


This capability will be changing as new use case requirements and field testing is performed. If you have any feature enhancements or issues with this feature, please contact RackN support.


The primary method for Digital Rebar Platform (DRP) to obtain control and manage the lifecycle of systems is via the in-band DHCP/PXE boot path. In some cases, this path may not be available due to network and security policy, or by operational principle.

The primary in-band DHCP/PXE path is dramatically faster, scales to 10s of thousands of systems, and is in general a much more reliable path. The Baseboard Management Controller (BMC, aka "IPMI", aka "redfish controller") on many enterprise grade systems often lock up and require soft or hard resets, is extremely slow to process the ISO virtual media boot path, and inconsistent from vendor to vendor.

Should you still need to mount ISOs through the BMC, this Operations document will help you to dynamically generate the Boot ISO and control your hardware via the BMC Virtual Media booting path.

Here is a short-ish (10 min) video demonstrating this feature:

Supported Platforms

Due to the customized and unique design of each BMC in different manufacturers' hardware platforms, the Virtual Media boot functions only work on limited platform types. Here is the current list of support in DRP by vendor.

Vendor Working? Notes
Dell Yes Tested with iDRAC 8 platforms. Untested on iDRAC 9.
HPE Maybe Tooling is in place to support HPE platforms, but not tested yet.
Lenovo Not Yet No integration completed yet, future versions should be supported.
Other N/A Cisco UCS, Supermicro, and possibly other platforms may be added in the future. At this time there is no projected delivery dates for these platforms.


For Technical Preview use of the VirtualMedia ISO Booting method, you must ensure the following prerequisites are met:

  • DRP Version: v4.6.0-alpha00.50 or newer
  • drp-community-content: v4.6.0-alpha00.154 or newer (*)
  • ipmi plugin: v4.6.0-alpha00.59 or newer
  • IPMI actions configured and working via the IPMI plugin
  • sledgehammer-builder: v4.6.0-alpha00.154 or newer (**)


A new version of the Sledgehammer BootEnv iso/tar must also be updated with the DRP Community Content update. There are enhancements in Sledgehammer to support this feature (eg drpcli bootenvs uploadiso sledgehammer).


Sledgehammer Builder is only required if you intend to create customized versions of Sledgehammer for the Boot ISO image, otherwise this content pack is not required.

The General Availability (GA) release v4.6.0 of all respective components should support this capability, however it may still be marked as a Technical Preview feature and not a production supported feature.

The new version of the Sledgehammer BootEnv ISO (technically it's a tarball), contains a new embedded tempalte cdboot.iso which is used in the dynamic generated per-machine custom ISO. In addition, Sledgehammer has been modified to allow injection of Static IP assignments to the Sledgehammer environment (in addition to the default DHCP IP address assignment method).

The Process

Process Overview

Digital Rebar Platform (DRP) will dynamically generate a custom bootable ISO that should successfully boot both Legacy and UEFI BIOS systems. The ISO utilizes GRUB2 as the boot method, which has extensive and broad support for a large number of systems (specifically the UEFI boot stack pieces).

To set a specific machine (or machines) to begin generating a dynamic generated boot ISO, the Machine must have the Param boot-virtual-iso set to the Boolean value True.

This param will then cause the dr-provision service to automatically generate the ISO when the Machine(s) change BootEnv in to the Sledgehammer BootEnv. There are several other Params that are used to inject custom details in to the dynamically generated ISO, which are described below.

In addition, DRP will automatically mount the dynamically generated ISO path location on the BMC, and attempt to set the Next Boot directive to boot via the VirtualMedia path.

The current usage path is as follows:

  • Set the boot-virtual-iso Param on the target machine(s)
  • Use drpcli to verify the dynamically generated ISO is set to mount to the Machine(s) BMC
  • Set any supporting customization Params (eg network-data static IP addressing)
  • Set the Machine(s) BootEnv to Sledgehammer (if currently in Sledgehammer, change it to local, then back to Sledgehammer).

The IPMI plugin must be installed, and have been configured for the Machine(s) that you are controlling. This is typically done in a discovery phase workflow with the use of the ipmi-inventory Stage.

More complete details in the below sections.

Enable Dynamic ISO Generation

For any machine(s) that you will attach Virtual Media ISOs to, you must set the following Params:

  • boot-virtual-iso to the Boolean value true
# example of setting machine 'mach-01' (a UUID can be used) to have dynamically generated ISOs
drpcli machines set Name:mach-01 param boot-virtual-iso to true

Once this value is set on the machine, and all appropriate Prerequisites fulfilled (listed above), then the dr-provision service will dynamically generate a custom ISO when the Machine is changed in to the Sledgehammer BootEnv.

The ISO will be built and cached at on the DRP server under the tftpboot path in a directory named dynamic_isos. In a typical "production" install mode, this is found at the following fully qualified path in a separate directory for each Machine, with the Machines UUID value:

  • /var/lib/dr-provision/tftpboot/dynamic_isos/<MACHINE_UUID>

Verify the Virtual Media ISO Mount

For the system to boot from the Virtual Media ISO - the Baseboard Management Controller (BMC) must be instructed to mount the ISO. This path is not very well standardized between the different manufacturers. Currently, the Redfish protocol is the only supported method for mounting the Virtual Media. However, there is no standardized Redfish path for setting the "bootonce" via VirtualMedia to the BMC. The IPMI plugin must be correctly configured to support the vendor specific capabilities to control the BMC (eg iDRAC or iLO) to support the reboot once to VirtualMedia.


BootEnv transitions will automatically attempt to set the VirtualMedia mount path, and set the appropriate boot once directive.

To verify the media mount path, the drpcli command line tool has been extended to support several Redfish query paths to check/set/verify/mount/unmount media on the BMCs Virtual Media mount point.

# verify the mount path (again, a Machine UUID can be specified instead of Name)
drpcli machines runaction Name:mach-01 statusVirtualMedia ipmi/mode redfish

An example output showing the automatically generated VirtualMedia mount path:

  "Image": "",
  "Inserted": true

The BMC web portal and other tools should also reflect this status.

Customize the Network Configuration

By default, the custom ISO will attempt to utilize DHCP on the first iterated network interface (eth0). If this behavior is not desired and needs changed; the use of the network-data Param structure can control the values.


This network-data structure MUST be added to the machine prior to the machine generating the custom ISO. Do not transition BootEnvs until the correct values have been set in this Param.

Here is an example Param stanza to define static IP assignment to a machine, as an example:

  "prov": {
    "address": "",
    "gateway": "",
    "interface": "eth10",
    "netmask": ""

It may also be possible (but is as of yet untested), to set a VLAN tag value for environments using VLAN tagging with the addition of the key/value pair "vlan": 1020.


This network-data structure can be used with the standard Sledgehammer PXE in-band boot path, and should allow you to set static IP assignments for Sledgehammer, disabling IP address acquisition via DHCP.

Boot From the VirtualMedia ISO

Once you have enabled the generation of the dynamic ISOs, set any specific network-data values required, and verified the VirtualMedia mount, you can now boot the system.

To boot in to the dynamic custom ISO - transition the Machine in to the Sledgehammer BootEnv.

If the Machine is already in the Sledgehammer BootEnv, you will need to change the machine to something else ( eg local BootEnv), then back to Sledgehammer.

Here is the example of transitioning a machine that is currently in Sledgehammer, to local, then setting the Workflow to discover-base; which defines Sledgehammer as the bootenv.

# remove workflow for machine named 'mach-01'
drpcli machines workflow Name:mach-01 ""

# set the BootEnv to local - expect up to 60 second wait for command to complete
drpcli machines bootenv Name:mach-01 local

# set workflow to 'discover-base', which specifies Sledgehammer bootenv
# again - wait up to 60 seconds for command to complete
drpcli machines workflow Name:mach-01 discover-base


The bootenv transition changes now trigger a dynamic ISO regeneration, and the VirtualMedia attach commands to the BMC. These operations are all slow, and take time. Patience, young Skywalker...

It is advised that you should watch the physical or virtual console to verify the machine boot process. You should see the system boot in to the Sledgehammer dynamically generated ISO. The process looks VERY similar to the boot process of the standard in-band DHCP/PXE boot process.

Notes and Troubleshooting

Here is a list of notes or debugging processes to help if there are issues with the VirtualMedia booting process.

Restore Default In-Band Management Path

If a machine object has been modified to use the out-of-band dynamically generated custom ISO, it can be returned to proper in-band management by simply removing the boot-virtual-iso Param from the machine, for example:

# remove the boot-virtual-iso param from machine Named 'mach-01'
drpcli machines remove Name:mach-01 param boot-virtual-media

In addition, the network-data param may or may not need to be removed. If moving back to DHCP IP address based PXE booting, then typically this param should be removed. However, the DHCP/PXE boot path process for in-band management of the system will still honor the settings in this param when Sledgehammer boots.

If complete clean up is required, you may also want to remove the dynamically generated ISO images in the tftpboot/dynamic_isos/ directory path. Note that ISOs are stored in a sub-directory with the Machines UUID as the directory name.

Performance Impact

Any command and control functions implemented directly to the Baseboard Management Controller (BMC) are generally extremely slow. Many commands described above will block and wait for 30 to 60 seconds before the command completes.

Additionally, with the boot-virtual-iso set to true, specific BootEnv changes force the dr-provision service to dynamically generate a new custom ISO. This process can be CPU and I/O intensive, especially if many machines are transitioned at once.

There is currently no sizing guidelines to for large scale infrastructure use of this feature. However, expect additional CPU and disk I/O impact.

Verifying the Boot to VirtualMedia

This process attempts to automatically set the VirtualMedia boot process and attach the dynamic generated ISO to the BMC VirtualMedia mount point. There are several ways to verify this has happened, including use of the vendor specific tooling, vendor BMC Web service, Redfish calls, etc. In addition, the drpcli client tool has support to manipulate and verify the boot process.

# verify the status - note this can take a long time to complete
drpcli machines runaction Name:mach-01 statusVirtualMedia ipmi/mode redfish

In addition, observing the Boot POST process of the Machine in question should yield visual clues. For example, Dell systems with iDRAC 8 BMCs would show output like:

  • IPMI: Boot to Virtual CD Requested

VirtualMedia Mount Options

The new actions in the IPMI plugin support manipulating the VirtualMedia mount paths, here are examples of different usage scenarios:

Mount ISO

# mount the dynamically generated ISO for the machine specified by UUID
# also set the boot once from virtual media option
drpcli machines runaction bb1eadf9-4b5e-46a7-a577-d07e2a33138f mountVirtualMedia ipmi/mode redfish ipmi/virtual-media-url ipmi/virtual-media-boot true

Unmount ISO

# by machine Name reference:
drpcli machines runaction Name:mach-01 unmountVirtualMedia ipmi/mode redfish

Perform Power Reboot via Redfish

# powercycle machine by name, using Redfish
drpcli machines runaction Name:mach-01 powercycle ipmi/mode redfish

Get Current Power Status

# get current power status using the default IPMI mode (redfish, ipmi protocol, or vendor specific)
drpcli machines runaction Name:mach-01 powerstatus

# get it specifically via the Redfish API
drpcli machines runaction Name:mach-01 powerstatus ipmi/mode redfish

Validate Dynamic ISO Generated

Virtual Media ISOs are generated and stored under the tftpboot directory structure, in the dynamic_isos directory. Each dynamic ISO for a Machine is stored in a sub-directory with the Machine's UUID. In a standard production install, this would be:

  • /var/lib/dr-provision/tftpboot/dynamic_isos/<MACHINE_UUID>/

After the Machine has transitioned into Sledgehammer, the ISO will be stored in this directory path, and the directory tree will look like the following:

cd /var/lib/dr-provision/tftpboot/dynamic_isos

tree bb1eadf9-4b5e-46a7-a577-d07e2a33138f/
├── local
└── sledgehammer
    └── boot.iso

2 directories, 1 file

Mounting the ISO and reviewing it's contents should show:

mount bb1eadf9-4b5e-46a7-a577-d07e2a33138f/sledgehammer/boot.iso /mnt
tree /mnt
├── boot
│   └── grub
│       ├── fonts
│       │   └── unicode.pf2
│       ├── grub.cfg
│       ├── i386-pc
│       │   ├── acpi.mod
│       │   ├── <...snip...>
│       │   └── zfs.mod
│       └── roms
├── boot.catalog
├── EFI
│   └── BOOT
│       ├── BOOT.conf
│       ├── BOOTIA32.EFI
│       ├── BOOTX64.EFI
│       ├── fonts
│       │   ├── TRANS.TBL
│       │   └── unicode.pf2
│       ├── grub.cfg
│       ├── grubia32.efi
│       ├── grubx64.efi
│       ├── mmia32.efi
│       ├── mmx64.efi
│       └── TRANS.TBL
├── stage1.img
└── vmlinuz0

8 directories, 292 files

The customizations to network configuration are written in to the GRUB boot config file, which can be verified as follows:

$ sudo cat /mnt/boot/grub/grub.cfg
if [ ${grub_platform} == "efi" ]; then
  set root=(cd0)
  set linuxcmd=linuxefi
  set initrdcmd=initrdefi
  set root=(cd)
  set linuxcmd=linux
  set initrdcmd=initrd
# There are 15 lines of 80 comments after for padding.
# replace here
menuentry "Sledgehammer" {
  $linuxcmd /vmlinuz0 BOOTIF=discovery rootflags=loop root=live:/sledgehammer.iso rootfstype=auto ro liveimg rd_NO_LUKS rd_NO_MD rd_NO_DM provisioner.web= rs.uuid=bb1eadf9-4b5e-46a7-a577-d07e2a33138f      provisioner.ip=   provisioner.interface="eth10"      -- console=ttyS0,115200 console=tty0
  $initrdcmd /stage1.img

The relevant customizations from the network-data structure are converted to the Sledgehammer menuentry stanza values (eg provisioner.ip,, etc.).


There are also a large number of "padding" pound sign characters, which is required for absurd and arcane GRUB reasons. Do not change them. You have been warned.