How the OnBoard appliance boots is introduced at a high level in Configuring the boot file location in the section on configuring boot in the Web Manager. The additional information in this section is to give an administrator who has the root password enough background to be able to boot from an alternate image if the need arises and if the Web Manager is not available.
The OnBoard appliance uses a U-Boot boot loader that resides in soldered Flash memory and that automatically runs at boot time. U-Boot boots the OnBoard appliance from an image whose location is configurable. The image can reside either in a separate removable Flash memory on the OnBoard appliance or on a boot server on the network.
Up to two images may be stored at the same time on the OnBoard appliance’s removable Flash. Each image on the removable Flash has three separate file systems mounted on three Linux partitions. The first partition for each image contains the kernel, the second partition contains the root filesystem mounted read only and the third partition contains the configuration files mounted read-write.
Refer to the following text and figure explaining partition numbers if needed for understanding the instructions about boot configuration As illustrated in the following figure, the first partition for each image contains the Linux kernel, the second partition contains the root-mounted filesystem (which is mounted read only), and the third partition (which is mounted read write) contains the configuration files.
The previous figure also shows a configuration backup partition (/dev/hda3 in removable Flash). This partition is mounted as /mnt/hda3. The /mnt/hda3/backup directory is used for storing compressed copies of backed-up configuration files, as shown in the following screen example.