GRUB2: Default Boot Loader and Manager in Ubuntu

than 0. The first device/drive is still hd0 by default (no change). These

designations can be altered if necessary in the device.map file in the

/boot/grub folder.

Automated searches for other operating systems, such as Windows, are

accomplished whenever update-grub is executed. Operating systems

found will be placed in the Grub 2 menu.

Changes made in the configuration files will not take effect until the

update-grub command is executed.

Upgrading to GRUB 2 From GRUB

GRUB 2 is the default bootloader for Ubuntu. Users who still have Grub 0.97

installed on their Ubuntu systems can upgrade to GRUB 2 by installing the

currently-supported releases of Ubuntu or by enabling repositories which

contain the GRUB 2 package grub-pc.

Please visit the Grub2/Upgrading community documentation for more

information and instructions.

File Structure

GRUB 2 incorporates a totally revised directory and file hierarchy. The major

GRUB 2 folders include /etc/grub.d, which contains the main GRUB 2 scripts,

and /boot/grub, which contains the GRUB 2 modules and menu file (grub.cfg).

User customizations are normally made to the /etc/default/grub file.

The description of the major GRUB 2 folders and files is located on the

Grub2/Setup community documentation page.

Configuring GRUB 2

Configuration changes are normally made to the /etc/default/grub file and to

the custom scripts located in /etc/grub.d. No changes are made to the GRUB 2

menu until the update-grub command is run as root. This command runs

the GRUB 2 configuration scripts and updates the /boot/grub/grub.cfg file.

Descriptions of the GRUB 2 options and how to change them are presented on

the Grub2/Setup community documentation page.

Boot Display Behavior

GRUB 2 loads before any operating system. Its modular components are

loaded on an as-needed basis. Menu display behavior is generally determined

by settings in /etc/default/grub. Review the "Configuring GRUB 2" section

above for specific entry and formatting guidance.

Initial Default

1 If no other operating system is detected GRUB 2 will boot straight into the

default operating system and no menu will be displayed.

2 If another operating system is detected the GRUB 2 menu will display.

Timed Display

1 The menu is displayed for a predetermined number of seconds. The default

entry is highlighted and other selections may be made by the user until

the timeout expires. The default timeout is 2 seconds. The timer

continues until any key is pressed or the highlighted entry is selected by

pressing ENTER.

2 If no user input is made GRUB 2 boots the default entry at the end of the

timeout period.

3 Once a key has been pressed the timeout is deactivated and the user must

make a selection manually.

4 The default entry is determined by the GRUB_DEFAULT= setting in

/etc/default/grub; the first "menuentry" has a value of "0".

Hidden

1 Normal Hidden Operations Enabled:

1

2

3

4

1

1

No menu entries are displayed. The splash screen, if configured, will

be displayed.

The time the screen remains blank but available for display is

determined by a setting in /etc/default/grub

(GRUB_HIDDEN_TIMEOUT)

GRUB 2 can display a countdown timer to provide visual feedback on

the time remaining until the default selection is chosen. The

timeout setting is enabled in /etc/default/grub

(GRUB_HIDDEN_TIMEOUT_QUIET)

The user may display the menu by pressing any key.

Once the menu displays, the GRUB_TIMEOUT counter begins.

Pressing any key stops the countdown.

If no key is pressed by the end of the timeout the default

entry determined by settings in /etc/default/grub will

be selected.

2 Hidden Menu Operations Not Expected (Abnormal):

1

The user may be able to display the menu in one or more of the

following ways:

1

1

2

Holding down the SHIFT key early in the boot process until the

menu displays.

GRUB 2 searches for a depressed SHIFT key signal during

boot. If the key is pressed or GRUB 2 cannot

determine the status of the key, the menu is

displayed.

Pressing the ESC key during a 3 second window as GRUB 2

runs.

Saved

1 Saving an OS can be achieved by running sudo grub-set-default if

GRUB_DEFAULT=saved is set in /etc/default/grub. It may also be saved

if GRUB_SAVEDEFAULT=true is also set in /etc/default/grub. In this

case, the default OS remains until a new OS is manually selected from

the GRUB 2 menu or the grub-set-default command is executed.

Last Boot Failed or Boot into Recovery

Mode

If the last boot failed or after a boot into Recovery Mode the menu will be

displayed until the user makes a selection.

To change this behaviour, edit /etc/default/grub and add the variable

GRUB_RECORDFAIL_TIMEOUT. Set the value similar to setting for

GRUB_TIMEOUT.

1 For -1, there will be no countdown and thus the menu will display.

2 For 0, menu will not display even for a failed startup.

3 For >=1, menu will display for the specified number of seconds.

Run update-grub after the change have been made.

In some cases trick with GRUB_RECORDFAIL_TIMEOUT doesn't work. In such

a case edit /etc/grub.d/00_header and change value of timeout in line

236 (this line is in the make_timeout() function)

set timeout=-1

to the the value as decribed above.

Run update-grub after the change have been made. Special thanks to

McCunha on Ubuntu Forums for the above tip.

The above change, however, still causes GRUB2 to boot into text graphics

mode. Thus, an additional change is required. Edit /etc/grub.d/10_linux

and change line 188 to

set linux_gfx_mode=keep

Once again, run update-grub after the change has been made.

Password Protection

GRUB 2 is capable of password-protecting menu editing, access to the GRUB 2

terminal, and specific or all menuentries. It can also limit access to specific

entries for specific users, and can encrypt plain-text passwords for increased

security. Please refer to the Grub2/Passwords community documentation.

Custom Menu Entries

GRUB 2 allows users to create customized menu selections which will be

automatically added to the main menu when sudo update-grub is

executed. A 40_custom file is available in /etc/grub.d/ for use or to serve as

an example to create other custom menus. Information on building and using

custom menus in GRUB 2 is located in the Grub2/CustomMenus community

document.

Troubleshooting

GRUB 2 provides excellent capabilities for troubleshooting and correcting boot

problems from the boot menu or GRUB 2 terminal. Troubleshooting and

recovery procedures are detailed in the Grub2/Troubleshooting community

document which also includes a section Selected_Problems_and_Bugs.

Fixing reboot/shutdown freezes

If your machine freezes upon attempts to shutdown or reboot, try modifying

/etc/default/grub. Open the file with gksudo gedit /etc/default/grub

(graphical interface) or sudo nano /etc/default/grub (command-line).

Any other plaintext editor (Vim, Emacs, Kate, Leafpad) is fine too. Find the line

that starts with GRUB_CMDLINE_LINUX_DEFAULT and add reboot=bios

to the end.

If done properly it should result in something like

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash reboot=bios"

Then save the file, run sudo update-grub and reboot in any way that's

possible for you. After that, reboots and shutdowns should start working

properly.

With certain hardware (notably DELL) the kernel parameter that you add

needs to be reboot=pci (instead of reboot=bios), the procedure remains

the same.

Displays

GRUB 2 can do more than provide a simple black & white menu. Its menu can

be customized by the user to present a more visually-appealing menu by

changing font colors, backgrounds and resolutions.

For information on using splash images and changing font colors and menu

resolutions, please refer to the Grub2/Displays community documentation.

Themes

GRUB 2 Theming is still under development, as is integration with gfxmenu.

Theme elements will include colors, fonts, progress indicators, menus, and

labels. Both of these hold great promise but are not ready for release with

Ubuntu 9.10. Check the Links section at the bottom of this page for

references.

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3

Installing/Reinstalling/Moving

GRUB2

Please visit the Grub2/Installing community documentation. Information

concerning upgrades from GRUB 0.97 (Legacy) to GRUB 2 is now located at

Grub2/Upgrading.

Booting an ISO from a Menuentry

Ubuntu ISOs, as well as many utility ISOs and some other Linux operating

systems, can be booted from a hard drive via a GRUB menuentry. This

eliminates the need to create a CD/DVD and allows bootable image files to be

stored only on the hard drive.

For information on this Grub 2 feature, please visit the Grub2/ISOBoot

community documentation page.

Security

Preventing booting via Grub command-line

The ability to manually boot using the Grub command-line constitutes the

biggest security risk in Linux. Any OS can be booted in this manner from any

USB or CD/DVD drive, circumventing BIOS restrictions. Placing passwords or

locking menu items (in the Grub configuration files) does not prevent a user

from booting manually using commands entered at the grub command-line.

(Once a foreign OS is booted, of course, it can be used to access any part of

an unencrypted hard drive).

There are currently no options to prevent the command-line usage of Grub.

Doing so would restrict boot-loading to just the menu options and that is not

considered wise

Miscellaneous

Booting from a serial console

If you want GRUB to operate over a serial line, you will need to uncomment

GRUB_TERMINAL in /etc/default/grub and set it to serial (instead of the

console default). Alternatively, you can add GRUB_TERMINAL="console serial"

to have the grub menu on both serial and local console. The default serial

console settings are to operate on the first serial port (ttyS0) at a 9600 bit/s

transfer rate with 8 data bits, 1 stop bit and no parity.

If you want to use another serial port or if your console uses different

settings, you must add a GRUB_SERIAL_COMMAND line to specify

additional parameters to the serial command. The serial command in GRUB 2

uses the same syntax as its GRUB Legacy counterpart (documented here). For

example, for a very common 9600 bit/s (baud) serial line with 8 data bits, 1

stop bit and no parity:

GRUB_SERIAL_COMMAND="serial --unit=0 --speed=9600 --

word=8 --parity=no --stop=1"

An example is a 4800 bit/s (baud) serial line with 7 data bits, 1 stop bit and

even parity:

GRUB_SERIAL_COMMAND="serial --unit=0 --speed=4800 --

word=7 --parity=even --stop=1"

Booting FreeBSD, NetBSD, and multiboot

OSes

Please refer to the article Grub2OtherOs community documentation page.

Links

1 Grub2/CustomMenus

2 Grub2/Displays

3 Grub2/Installing

4 Grub2/ISOBoot

5 Grub2/Setup

6 Grub2/Passwords

7 Grub2/Submenus

8 Grub2/Troubleshooting

9 Grub2/Upgrading

10

Grub 2 (Ubuntu Wiki)

External Links

1 GNU GRUB

2 GNU GRUB2 Manual

3 Illustrated Dual Boot HomePage

4 Mac OS X (XNU) Support

5 Mac OS X Boot Snow Leopard

6 GRUB Manual - Themes

7 The Definitive Guide to Theming GRUB2 by Towheed Mohammed

Analysis of problems with grub2 and RAID1 with workarounds