Cisco Systems Comprehensive CSR 1000V Ordering Guide: Accessing and Using GRUB Mode

C H A P T E R 11

Accessing and Using GRUB Mode

•About GRUB Mode and the Configuration Register

•Accessing GRUB Mode

•Using the GRUB Menu

•Modifying the Configuration Register (confreg)

•Changing the Configuration Register Settings

•Displaying the Configuration Register Settings

About GRUB Mode and the Configuration Register

The Cisco CSR 1000V has a 16-bit configuration register in NVRAM. Each bit has value 1 (on or set) or value 0 (off or clear), and each bit setting affects the router behavior upon the next reload power cycle. The Cisco CSR 1000V GRUB mode supports a subset of configuration register options compared to ROMMON options on other Cisco routers.

You can use the configuration register to:

•Force the router to boot into the GRUB (bootstrap program)

•Select a boot source and default boot filename

•Recover a lost password

Table 11-1describes the configuration register bits.

Table 11-1	Configuration Register Bit Descriptions
Bit
Number	Hexadecimal	Meaning
00–03	0x0000–0x000F	Boot field. The boot field setting determines whether the router loads an
		operating system and where it obtains the system image.
		See Table 11-2for details.
06	0x0040	Causes the system software to ignore the contents of NVRAM. This can
		be used for password recovery.

	Cisco CSR 1000V Series Cloud Services Router Software Configuration Guide
OL-27477-07		11-1