- GRUB2 is the default boot loader from Ubuntu 9.10.
- To determine which version of GRUB is installed, use the following command:
grub-install -v
- The grub configuration file is “/boot/grub/grub.cfg” .
- The “grub.cfg” file is updated using the script files located in the folder “/etc/grub.d/” and the file “/etc/default/grub”.
- The script files located in the “/etc/grub.d/” folder are the following:
| File | Purpose of the File |
| 00_header | For setting environment variable |
| 05_debian_theme | Setting the GRUB2 menu theme |
| 10_linux | For adding the kernels of Ubuntu to GRUB2Menu |
| 20_memtest86+ | For adding memtest86+ to the GRUB2 menu |
| 30_os-prober | For adding other OSs loaded in the system |
| 30_uefi-firmwire | For adding entry related to UEFI firmwire |
| 40_custom | For adding custom menu entries to GRUB2 menu |
- The file “/etc/default/grub” contains the GRUB2 menu configuration values like timeout, background picture location, default entry, etc…
- The command used to update the “grub.cfg” file is “update-grub” .
- The command will execute the script file in the order of numerical values appended before their name.
A sample “grub.cfg” entry
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#
### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
set have_grubenv=true
load_env
fi
set default="0"
if [ x"${feature_menuentry_id}" = xy ]; then
menuentry_id_option="--id"
else
menuentry_id_option=""
fi
export menuentry_id_option
if [ "${prev_saved_entry}" ]; then
set saved_entry="${prev_saved_entry}"
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi
function savedefault {
if [ -z "${boot_once}" ]; then
saved_entry="${chosen}"
save_env saved_entry
fi
}
function recordfail {
set recordfail=1
if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}
function load_video {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
else
insmod efi_gop
insmod efi_uga
insmod ieee1275_fb
insmod vbe
insmod vga
insmod video_bochs
insmod video_cirrus
fi
}
if [ x$feature_default_font_path = xy ] ; then
font=unicode
else
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
font="/usr/share/grub/unicode.pf2"
fi
if loadfont $font ; then
set gfxmode=auto
load_video
insmod gfxterm
set locale_dir=$prefix/locale
set lang=en_IN
insmod gettext
fi
terminal_output gfxterm
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
insmod jpeg
background_image -m stretch /home/sreeraj/Pictures/1.jpg
if [ "${recordfail}" = 1 ]; then
set timeout=-1
else
set timeout=100
fi
set superusers="sreeraj"
password sreeraj l2o9i7b5
### END /etc/grub.d/00_header ###
### BEGIN /etc/grub.d/05_debian_theme ###
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
insmod jpeg
if background_image /home/sreeraj/Pictures/1.jpg; then
set color_normal=black/black
set color_highlight=black/green
true
else
set menu_color_normal=red/black
set menu_color_highlight=black/light-gray
if background_color 44,0,30; then
clear
fi
fi
### END /etc/grub.d/05_debian_theme ###
### BEGIN /etc/grub.d/10_linux ###
function gfxmode {
set gfxpayload="${1}"
if [ "${1}" = "keep" ]; then
set vt_handoff=vt.handoff=7
else
set vt_handoff=
fi
}
if [ "${recordfail}" != 1 ]; then
if [ -e ${prefix}/gfxblacklist.txt ]; then
if hwmatch ${prefix}/gfxblacklist.txt 3; then
if [ ${match} = 0 ]; then
set linux_gfx_mode=keep
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=text
fi
else
set linux_gfx_mode=keep
fi
else
set linux_gfx_mode=text
fi
export linux_gfx_mode
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-fee98781-9046-4ee7-b7d2-e9017c5caa4a' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
linux /boot/vmlinuz-3.8.0-19-generic root=UUID=fee98781-9046-4ee7-b7d2-e9017c5caa4a ro noquite splash $vt_handoff
initrd /boot/initrd.img-3.8.0-19-generic
}
submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-fee98781-9046-4ee7-b7d2-e9017c5caa4a' {
menuentry 'Ubuntu, with Linux 3.8.0-19-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.8.0-19-generic-advanced-fee98781-9046-4ee7-b7d2-e9017c5caa4a' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
echo 'Loading Linux 3.8.0-19-generic ...'
linux /boot/vmlinuz-3.8.0-19-generic root=UUID=fee98781-9046-4ee7-b7d2-e9017c5caa4a ro noquite splash $vt_handoff
echo 'Loading initial ramdisk ...'
initrd /boot/initrd.img-3.8.0-19-generic
}
menuentry 'Ubuntu, with Linux 3.8.0-19-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.8.0-19-generic-recovery-fee98781-9046-4ee7-b7d2-e9017c5caa4a' {
recordfail
load_video
insmod gzio
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
echo 'Loading Linux 3.8.0-19-generic ...'
linux /boot/vmlinuz-3.8.0-19-generic root=UUID=fee98781-9046-4ee7-b7d2-e9017c5caa4a ro recovery nomodeset
echo 'Loading initial ramdisk ...'
initrd /boot/initrd.img-3.8.0-19-generic
}
}
### END /etc/grub.d/10_linux ###
### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###
### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
linux16 /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
insmod part_msdos
insmod ext2
set root='hd0,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 fee98781-9046-4ee7-b7d2-e9017c5caa4a
else
search --no-floppy --fs-uuid --set=root fee98781-9046-4ee7-b7d2-e9017c5caa4a
fi
linux16 /boot/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###
### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###
### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###
### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###
### BEGIN /etc/grub.d/41_custom ###
if [ -f ${config_directory}/custom.cfg ]; then
source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then
source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###
A sample “/etc/default/grub” entry
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'
GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=100
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="noquite splash"
GRUB_CMDLINE_LINUX=""
GRUB_BACKGROUND="/home/sreeraj/Pictures/1.jpg"
# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"
# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true
# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
