Chapter 14. Aboot

Aboot is the bootloader for EOS. The bootloader is a small program that loads automatically when the system is powered on. The bootloader’s primary job is to load the primary operating system (OS), 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.


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, whereas 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 in Linux:

[admin@Arista ~]$ cd /mnt/flash
[admin@Arista flash]$ ls
EOS-4.20.1F.swi  debug    schedule        zerotouch-config
boot-config      persist  startup-config

Aboot reads the contents of this file, determines the image to be loaded, and then loads it. If the boot-config 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 is corrupt or not found

  • Configured EOS image is corrupt or not found

  • Ctrl-C is entered from the console while the ...

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