GRUB Commands

GRUB allows a number of useful commands in its command line interface. Some of the commands accept options after their name, and these options should be separated from the command and other options on that line by space characters.

The following is a list useful commands:

• boot — Boots the operating system or chain loader that has been previously specified and loaded.

• chainloader <file-name> — Loads the specified file as a chain loader. To grab the file at the first sector of the specified partition, use +1 as the file's name.

• displaymem — Displays the current use of memory, based on information from the BIOS. This is useful to determine how much RAM a system has prior to booting it.

• initrd <file-name> — Enables users to specify an initial RAM disk to use when booting. An initrd is necessary when the kernel needs certain modules in order to boot properly, such as when the root partition is formated with the ext3 file system.

• install <stage-1> <install-disk> <stage-2> p <config-file> — Installs GRUB to the system MBR.

  	Warning
  	The install command will overwrite any other information in the MBR. If executed, any information (other than GRUB information) that is used to boot other operating systems, will be lost. Make sure you know what you are doing before executing this command.

  This command can be configured in several different ways. However, it is required to specify a <stage-1>, which signifies a device, partition, and file where the first boot loader image can be found, such as (hd0,0)/grub/stage1. In addition, specify the disk where the stage 1 boot loader should be installed, such as (hd0).

  The <stage-2> section tells the stage 1 boot loader where the stage 2 boot loader is located, such as (hd0,0)/grub/stage2. The p option tells the install command that a menu configuration file is being specified in the <config-file> section, such as (hd0,0)/grub/grub.conf.

• kernel <kernel-file-name> <option-1> <option-N> — Specifies the kernel file to load from GRUB's root filesystem when using direct loading to boot the operating system. Options can follow the kernel command and will be passed to the kernel when it is loaded.

  For Red Hat Linux, an example kernel command looks like the following:

  kernel /vmlinuz root=/dev/hda5

  This line specifies that the vmlinuz file is loaded from GRUB's root filesystem, such as (hd0,0). An option is also passed to the kernel specifying that the root filesystem for the Linux kernel when it loads should be on hda5, the fifth partition on the first IDE hard drive. Multiple options may be placed after this option, if needed.

• root <device-and-partition> — Configures GRUB's root partition to be the particular device and partition, such as (hd0,0), and mounts the partition so that files can be read.

• rootnoverify <device-and-partition> — Does the same thing as the root command but does not mount the partition.

Commands other than these are available. Type info grub for a full list of commands.