#Name

Boot Device Addressing - addressing the correct boot device to use.

#Synopsis

Serenity's kernel can select the boot device at boot time, based on the root boot parameter. This functionality is used to control which boot device is selected to be used for all further boot process operations.

#Description

The kernel root boot parameter takes the form of root={value}, where the ={value} trailer can be set to specific prefixes to indicate the boot device preference.

#Addressing options

The user can choose to use addressing based on synthetic unix concepts:

block0:0

This is especially useful in static hardware setups, so the user can choose to use either a raw StorageDevice or partition block device. The 0,0 selection is the MAJOR,MINOR numbers of the device.

However, when there's knowledge of the hardware arrangement of raw StorageDevices, it could be valuable to use addressing based on hardware-relative interface-specific "location" to address raw StorageDevices:

ata0:0:0 [First ATA controller, ATA first primary channel, master device]
nvme0:1:0 [First NVMe Controller, First NVMe Namespace, Not Applicable]
ramdisk0 [First Ramdisk]

When the logical arrangement is known, using (absolute) LUNs is the easiest option as it doesn't rely on using unix device numbers or hardware-relative location:

lun0:0:0 - first device on the first channel of the first controller to be enumerated

#Note on selecting partitions from raw StorageDevices

All the addressing options above support selecting a partition device, given that the selected device is a StorageDevice and not a DiskPartition device:

nvme0;part0
lun0:0:0;part0

The only exception to this is when choosing a BlockDevice. As such, trying to specify block0:0;part0, for example, will lead to a kernel panic, as an invalid boot device parameter.

#Selecting a specific partition based on known GUID

For GPT partitions, passing PARTUUID: and the GUID of the partition can be used to select a GPT partition. Although it could be slower to find the corresponding partition, it is the safest option available for persistent storage.