Cisco Systems CSR 1000V Accessing and Using GRUB Mode

CHAPT ER
11-1
Cisco CSR 1000V Series Cloud Services Router Software Configuration Guide
OL-27477-07
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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
Table11-1 describes the configuration register bits.
Table11-1 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 Table11-2 for details.
06 0x0040 Causes the system software to ignore the contents of NVRAM. This can
be used for password recovery.