October 2012
Intermediate to advanced
419 pages
10h 47m
English
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Chapter 18. Aboot
Aboot is the bootloader for EOS in an Arista switch. The bootloader is a small program that loads automatically (often from nonvolatile ROM on a switch) when the system is powered on. The bootloader’s primary job is to load the primary operating system, which is usually stored elsewhere, such as flash memory or disk. If you’ve ever installed a Linux system, you’ve likely encountered bootloaders such as GRUB. On Windows NT/2000/XP machines, the default bootloader is NTLDR.
Note
Technically, there are two types of bootloaders: first stage and second stage. The first-stage bootloader usually operates at a very low level and is often responsible for hardware system checks. A PC’s BIOS would be considered a first-stage bootloader, while the bootloaders mentioned in this chapter would be second-stage bootloaders.
Before EOS is loaded, the switch loads the Aboot process from ROM. Aboot looks for a file called boot-config in flash:/, which to be painfully accurate, is actually /mnt/flash:
[admin@Arista flash]$ls /mnt/flashEOS-4.7.8.swiboot-configfullrecover schedule zerotouch-config EOS-4.8.1.swi debug persist startup-config
Aboot reads the contents of this file, determines the image to be
loaded, and then loads it. If the boot-config file does
not exist, Aboot will halt the system and present an Aboot# prompt. In fact, if any of the following
should occur, Aboot will halt the system:
boot-config file is corrupt or not found
Configured EOS image is corrupt or not found
Control-C ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.