<s>
GNU	B-Application
GRUB	I-Application
(	O
short	O
for	O
GNU	B-Operating_System
GRand	B-Application
Unified	I-Application
Bootloader	I-Application
,	O
commonly	O
referred	O
to	O
as	O
GRUB	B-Application
)	O
is	O
a	O
boot	B-Application
loader	I-Application
package	O
from	O
the	B-Application
GNU	I-Application
Project	I-Application
.	O
</s>
<s>
GRUB	B-Application
is	O
the	O
reference	O
implementation	O
of	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
's	O
Multiboot	O
Specification	O
,	O
which	O
provides	O
a	O
user	O
the	O
choice	O
to	O
boot	O
one	O
of	O
multiple	O
operating	B-General_Concept
systems	I-General_Concept
installed	O
on	O
a	O
computer	O
or	O
select	O
a	O
specific	O
kernel	B-Operating_System
configuration	O
available	O
on	O
a	O
particular	O
operating	B-General_Concept
system	I-General_Concept
's	O
partitions	O
.	O
</s>
<s>
GNU	B-Application
GRUB	I-Application
was	O
developed	O
from	O
a	O
package	O
called	O
the	O
Grand	B-Application
Unified	I-Application
Bootloader	I-Application
(	O
a	O
play	O
on	O
Grand	O
Unified	O
Theory	O
)	O
.	O
</s>
<s>
It	O
is	O
predominantly	O
used	O
for	O
Unix-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
The	B-Operating_System
GNU	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
uses	O
GNU	B-Application
GRUB	I-Application
as	O
its	O
boot	B-Application
loader	I-Application
,	O
as	O
do	O
most	O
Linux	B-Application
distributions	I-Application
and	O
the	O
Solaris	B-Application
operating	I-Application
system	I-Application
on	O
x86	B-Operating_System
systems	O
,	O
starting	O
with	O
the	O
Solaris	B-Application
10	I-Application
1/06	O
release	O
.	O
</s>
<s>
When	O
a	O
computer	O
is	O
turned	O
on	O
,	O
its	O
BIOS	B-Operating_System
finds	O
the	O
primary	O
bootable	O
device	O
(	O
usually	O
the	O
computer	O
's	O
hard	O
disk	O
)	O
and	O
runs	O
the	O
initial	O
bootstrap	O
program	O
from	O
the	O
master	B-Device
boot	I-Device
record	I-Device
(	O
MBR	B-Device
)	O
.	O
</s>
<s>
The	O
MBR	B-Device
is	O
the	O
first	O
sector	B-Application
of	O
the	O
hard	O
disk	O
.	O
</s>
<s>
This	O
bootstrap	O
program	O
must	O
be	O
small	O
because	O
it	O
has	O
to	O
fit	O
in	O
a	O
single	O
sector	B-Application
.	O
</s>
<s>
For	O
a	O
long	O
time	O
,	O
the	O
size	O
of	O
a	O
sector	B-Application
has	O
been	O
512bytes	O
.	O
</s>
<s>
Since	O
2009	O
there	O
are	O
hard	O
disks	O
available	O
with	O
a	O
sector	B-Application
size	O
of	O
4096bytes	O
,	O
called	O
Advanced	B-Device
Format	I-Device
disks	O
,	O
but	O
,	O
such	O
hard	O
disks	O
are	O
still	O
accessed	O
in	O
512-byte	O
sectors	O
,	O
using	O
the	O
512e	O
emulation	O
.	O
</s>
<s>
The	O
legacy	O
MBR	B-Device
partition	O
table	O
supports	O
a	O
maximum	O
of	O
four	O
partitions	O
and	O
occupies	O
64bytes	O
,	O
combined	O
.	O
</s>
<s>
Together	O
with	O
the	O
optional	O
disk	O
signature	O
(	O
four	O
bytes	O
)	O
and	O
disk	O
timestamp	O
(	O
six	O
bytes	O
)	O
,	O
this	O
leaves	O
between	O
434	O
and	O
446bytes	O
available	O
for	O
the	O
machine	B-Language
code	I-Language
of	O
a	O
boot	B-Application
loader	I-Application
.	O
</s>
<s>
Although	O
such	O
a	O
small	O
space	O
can	O
be	O
sufficient	O
for	O
very	O
simple	O
boot	B-Application
loaders	I-Application
,	O
it	O
is	O
not	O
big	O
enough	O
to	O
contain	O
a	O
boot	B-Application
loader	I-Application
supporting	O
complex	O
and	O
multiple	O
file	B-Application
systems	I-Application
,	O
menu-driven	O
selection	O
of	O
boot	O
choices	O
,	O
etc	O
.	O
</s>
<s>
Boot	B-Application
loaders	I-Application
with	O
bigger	O
footprints	O
are	O
therefore	O
split	O
into	O
pieces	O
,	O
where	O
the	O
smallest	O
piece	O
fits	O
in	O
the	O
MBR	B-Device
,	O
while	O
one	O
or	O
more	O
larger	O
pieces	O
are	O
stored	O
in	O
other	O
locations	O
such	O
as	O
empty	O
sectors	O
between	O
the	O
MBR	B-Device
and	O
the	O
first	O
partition	O
.	O
</s>
<s>
The	O
code	O
in	O
the	O
MBR	B-Device
then	O
does	O
little	O
more	O
than	O
starting	O
the	O
second	O
part	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
remaining	O
part(s )	O
of	O
the	O
boot	B-Application
loader	I-Application
is	O
to	O
actually	O
boot	O
an	O
operating	B-General_Concept
system	I-General_Concept
by	O
configuring	O
it	O
and	O
starting	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
Kernels	B-Operating_System
are	O
in	O
most	O
cases	O
stored	O
as	O
files	O
residing	O
on	O
appropriate	O
file	B-Application
systems	I-Application
,	O
but	O
the	O
concept	O
of	O
a	O
file	B-Application
system	I-Application
is	O
unknown	O
to	O
the	O
BIOS	B-Operating_System
.	O
</s>
<s>
Thus	O
,	O
in	O
BIOS-based	O
systems	O
,	O
the	O
duty	O
of	O
a	O
boot	B-Application
loader	I-Application
is	O
to	O
access	O
the	O
content	O
of	O
those	O
files	O
,	O
so	O
it	O
can	O
be	O
loaded	O
into	O
the	O
RAM	B-Architecture
and	O
executed	O
.	O
</s>
<s>
One	O
possible	O
approach	O
for	O
boot	B-Application
loaders	I-Application
is	O
to	O
load	O
kernel	B-Operating_System
images	I-Operating_System
by	O
directly	O
accessing	O
hard	O
disk	B-Application
sectors	I-Application
without	O
understanding	O
the	O
underlying	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Usually	O
,	O
an	O
additional	O
level	O
of	O
indirection	O
is	O
required	O
,	O
in	O
form	O
of	O
maps	O
or	O
map	O
files	O
auxiliary	O
files	O
that	O
contain	O
a	O
list	O
of	O
physical	O
sectors	O
occupied	O
by	O
kernel	B-Operating_System
images	I-Operating_System
.	O
</s>
<s>
Such	O
maps	O
need	O
to	O
be	O
updated	O
each	O
time	O
a	O
kernel	B-Operating_System
image	I-Operating_System
changes	O
its	O
physical	O
location	O
on	O
disk	O
,	O
due	O
to	O
installing	O
new	O
kernel	B-Operating_System
images	I-Operating_System
,	O
file	B-Application
system	I-Application
defragmentation	O
,	O
etc	O
.	O
</s>
<s>
Also	O
,	O
in	O
case	O
of	O
the	O
maps	O
changing	O
their	O
physical	O
location	O
,	O
their	O
locations	O
need	O
to	O
be	O
updated	O
within	O
the	O
boot	B-Application
loader	I-Application
's	O
MBR	B-Device
code	O
,	O
so	O
the	O
sectors	O
indirection	O
mechanism	O
continues	O
to	O
work	O
.	O
</s>
<s>
Another	O
approach	O
is	O
to	O
make	O
a	O
boot	B-Application
loader	I-Application
aware	O
of	O
the	O
underlying	O
file	B-Application
systems	I-Application
,	O
so	O
kernel	B-Operating_System
images	I-Operating_System
are	O
configured	O
and	O
accessed	O
using	O
their	O
actual	O
file	B-Application
paths	I-Application
.	O
</s>
<s>
That	O
requires	O
a	O
boot	B-Application
loader	I-Application
to	O
contain	O
a	O
driver	O
for	O
each	O
of	O
the	O
supported	O
file	B-Application
systems	I-Application
,	O
so	O
they	O
can	O
be	O
understood	O
and	O
accessed	O
by	O
the	O
boot	B-Application
loader	I-Application
itself	O
.	O
</s>
<s>
This	O
approach	O
eliminates	O
the	O
need	O
for	O
hardcoded	O
locations	O
of	O
hard	O
disk	B-Application
sectors	I-Application
and	O
existence	O
of	O
map	O
files	O
,	O
and	O
does	O
not	O
require	O
MBR	B-Device
updates	O
after	O
kernel	B-Operating_System
images	I-Operating_System
are	O
added	O
or	O
moved	O
around	O
.	O
</s>
<s>
The	O
configuration	O
of	O
a	O
boot	B-Application
loader	I-Application
is	O
stored	O
in	O
a	O
regular	O
file	O
,	O
which	O
is	O
also	O
accessed	O
in	O
a	O
file	O
system-aware	O
way	O
to	O
obtain	O
boot	O
configurations	O
before	O
the	O
actual	O
booting	O
of	O
any	O
kernel	B-Operating_System
images	I-Operating_System
.	O
</s>
<s>
As	O
a	O
downside	O
,	O
such	O
boot	B-Application
loaders	I-Application
are	O
larger	O
and	O
more	O
complex	O
.	O
</s>
<s>
GNU	B-Application
GRUB	I-Application
uses	O
the	O
second	O
approach	O
,	O
by	O
understanding	O
the	O
underlying	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
The	O
boot	B-Application
loader	I-Application
itself	O
is	O
split	O
into	O
multiple	O
stages	O
so	O
that	O
it	O
fits	O
in	O
the	O
MBR	B-Device
boot	O
scheme	O
.	O
</s>
<s>
Two	O
major	O
versions	O
of	O
GRUB	B-Application
are	O
in	O
common	O
use	O
:	O
GRUB	B-Application
version	O
1	O
,	O
called	O
GRUB	B-Application
legacy	O
,	O
is	O
only	O
prevalent	O
in	O
older	O
releases	O
of	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
GRUB	B-Application
2	I-Application
was	O
written	O
from	O
scratch	O
and	O
intended	O
to	O
replace	O
its	O
predecessor	O
,	O
and	O
is	O
now	O
used	O
by	O
a	O
majority	O
of	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
GRUB	B-Application
0.x	O
follows	O
a	O
two-stage	O
approach	O
.	O
</s>
<s>
The	O
master	B-Device
boot	I-Device
record	I-Device
(	O
MBR	B-Device
)	O
usually	O
contains	O
GRUB	B-Application
stage	O
1	O
,	O
or	O
can	O
contain	O
a	O
standard	O
MBR	B-Device
implementation	O
which	O
chainloads	B-Operating_System
GRUB	B-Application
stage	O
1	O
from	O
the	O
active	O
partition	B-Device
's	I-Device
boot	I-Device
sector	I-Device
.	O
</s>
<s>
Given	O
the	O
small	O
size	O
of	O
a	O
boot	O
sector	B-Application
(	O
512bytes	O
)	O
,	O
stage	O
1	O
can	O
do	O
little	O
more	O
than	O
load	O
the	O
next	O
stage	O
of	O
GRUB	B-Application
by	O
loading	O
a	O
few	O
disk	B-Application
sectors	I-Application
from	O
a	O
fixed	O
location	O
near	O
the	O
start	O
of	O
the	O
disk	O
(	O
within	O
its	O
first	O
1024	O
cylinders	O
)	O
.	O
</s>
<s>
Stage	O
1	O
can	O
load	O
stage	O
2	O
directly	O
,	O
but	O
it	O
is	O
normally	O
set	O
up	O
to	O
load	O
the	O
stage	O
1.5.	O
,	O
located	O
in	O
the	O
first	O
30	O
KiB	O
of	O
hard	O
disk	O
immediately	O
following	O
the	O
MBR	B-Device
and	O
before	O
the	O
first	O
partition	O
.	O
</s>
<s>
In	O
case	O
this	O
space	O
is	O
not	O
available	O
(	O
unusual	O
partition	O
table	O
,	O
special	O
disk	O
drivers	O
,	O
GPT	B-Application
or	O
LVM	B-Application
disk	O
)	O
the	O
install	O
of	O
stage	O
1.5	O
will	O
fail	O
.	O
</s>
<s>
The	O
stage	O
1.5	O
image	O
contains	O
file	B-Application
system	I-Application
drivers	O
,	O
enabling	O
it	O
to	O
directly	O
load	O
stage	O
2	O
from	O
any	O
known	O
location	O
in	O
the	O
filesystem	B-Application
,	O
for	O
example	O
from	O
/boot/grub	O
.	O
</s>
<s>
boot.img	O
(	O
stage	O
1	O
)	O
is	O
written	O
to	O
the	O
first	O
440bytes	O
of	O
the	O
Master	B-Device
Boot	I-Device
Record	I-Device
(	O
MBR	B-Device
boot	O
code	O
in	O
sector	B-Application
0	O
)	O
,	O
or	O
optionally	O
in	O
a	O
partition	B-Device
boot	I-Device
sector	I-Device
(	O
PBR	O
)	O
.	O
</s>
<s>
The	O
actual	O
sector	B-Application
number	O
is	O
written	O
by	O
grub-install	O
.	O
</s>
<s>
diskboot.img	O
is	O
the	O
first	O
sector	B-Application
of	O
core.img	O
with	O
the	O
sole	O
purpose	O
to	O
load	O
the	O
rest	O
of	O
core.img	O
identified	O
by	O
LBA	O
sector	B-Application
numbers	O
also	O
written	O
by	O
grub-install	O
.	O
</s>
<s>
On	O
MBR	B-Device
partitioned	O
disks	O
,	O
core.img	O
(	O
stage	O
1.5	O
)	O
is	O
stored	O
in	O
the	O
empty	O
sectors	O
(	O
if	O
available	O
)	O
between	O
the	O
MBR	B-Device
and	O
the	O
first	O
partition	O
.	O
</s>
<s>
Recent	O
operating	B-General_Concept
systems	I-General_Concept
suggest	O
a	O
1	O
MiB	O
gap	O
here	O
for	O
alignment	O
(	O
2047*512	O
byte	O
or	O
255*4KiB	O
sectors	O
)	O
.	O
</s>
<s>
This	O
gap	O
used	O
to	O
be	O
62	O
sectors	O
(	O
31	O
KiB	O
)	O
as	O
a	O
reminder	O
of	O
the	O
sector	B-Application
number	O
limit	O
of	O
Cylinder-Head-Sector	B-Device
(	O
C/H/S	B-Device
)	O
addressing	O
used	O
by	O
BIOS	B-Operating_System
before	O
1996	O
,	O
therefore	O
core.img	O
is	O
designed	O
to	O
be	O
smaller	O
than	O
32	O
KiB	O
.	O
</s>
<s>
On	O
GPT	B-Application
partitioned	O
disks	O
core.img	O
is	O
written	O
to	O
its	O
own	O
partition	O
.	O
</s>
<s>
It	O
must	O
be	O
flagged	O
"	O
BIOS_grub	O
"	O
,	O
must	O
not	O
be	O
formatted	B-Application
and	O
can	O
be	O
as	O
tiny	O
as	O
1	O
MiB	O
.	O
</s>
<s>
stage	O
2	O
:	O
core.img	O
loads	O
/boot/grub/i386-pc/normal.mod	O
from	O
the	O
partition	O
configured	O
by	O
grub-install	O
.	O
</s>
<s>
If	O
the	O
partition	O
index	O
has	O
changed	O
,	O
GRUB	B-Application
will	O
be	O
unable	O
to	O
find	O
the	O
normal.mod	O
,	O
and	O
presents	O
the	O
user	O
with	O
the	O
GRUB	B-Application
Rescue	O
prompt	O
.	O
</s>
<s>
Depending	O
on	O
how	O
GRUB2	O
was	O
installed	O
,	O
the	O
/boot/grub/	O
is	O
either	O
in	O
the	O
root	O
partition	O
of	O
the	O
Linux	B-Application
distribution	I-Application
,	O
or	O
in	O
the	O
separate	O
/boot	O
partition	O
.	O
</s>
<s>
after	O
normal.mod	O
loaded	O
:	O
normal.mod	O
parses	O
/boot/grub/grub.cfg	O
,	O
optionally	O
loads	O
modules	O
(	O
eg	O
.	O
</s>
<s>
for	O
graphical	O
UI	O
and	O
file	B-Application
system	I-Application
support	O
)	O
and	O
shows	O
the	O
menu	O
.	O
</s>
<s>
/efi/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1/grubx64.efi	O
(	O
for	O
x64	B-Device
UEFI	B-Architecture
systems	O
)	O
is	O
installed	O
as	O
a	O
file	O
in	O
the	O
EFI	B-Device
System	I-Device
Partition	I-Device
,	O
and	O
booted	O
by	O
the	O
firmware	O
directly	O
,	O
without	O
a	O
boot.img	O
in	O
MBR	B-Device
sector	B-Application
0	O
.	O
</s>
<s>
/boot/grub/	O
can	O
be	O
installed	O
on	O
the	O
EFI	B-Device
System	I-Device
Partition	I-Device
or	O
the	O
separate	O
/boot	O
partition	O
.	O
</s>
<s>
For	O
x64	B-Device
UEFI	B-Architecture
systems	O
,	O
stage2	O
are	O
the	O
/boot/grub/x86_64-efi/normal.mod	O
file	O
and	O
other	O
/boot/grub/	O
files	O
.	O
</s>
<s>
GRUB	B-Application
presents	O
a	O
menu	O
where	O
the	O
user	O
can	O
choose	O
from	O
operating	B-General_Concept
systems	I-General_Concept
(	O
OS	O
)	O
found	O
by	O
grub-install	O
.	O
</s>
<s>
GRUB	B-Application
can	O
be	O
configured	O
to	O
automatically	O
load	O
a	O
specified	O
OS	O
after	O
a	O
user-defined	O
timeout	O
.	O
</s>
<s>
In	O
the	O
operating	B-General_Concept
system	I-General_Concept
selection	O
menu	O
GRUB	B-Application
accepts	O
a	O
couple	O
of	O
commands	O
:	O
</s>
<s>
By	O
pressing	O
,	O
it	O
is	O
possible	O
to	O
edit	O
kernel	B-Operating_System
parameters	O
of	O
the	O
selected	O
menu	O
item	O
before	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
started	O
.	O
</s>
<s>
The	O
reason	O
for	O
doing	O
this	O
in	O
GRUB	B-Application
(	O
i.e.	O
</s>
<s>
Using	O
the	O
kernel	B-Operating_System
parameters	O
line	O
it	O
is	O
possible	O
,	O
among	O
other	O
things	O
,	O
to	O
specify	O
a	O
module	O
to	O
be	O
disabled	O
(	O
blacklisted	O
)	O
for	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
This	O
could	O
be	O
required	O
if	O
the	O
specific	O
kernel	B-Operating_System
module	O
is	O
broken	O
and	O
thus	O
prevents	O
boot-up	O
.	O
</s>
<s>
For	O
example	O
,	O
to	O
blacklist	O
the	O
kernel	B-Operating_System
module	O
nvidia-current	O
,	O
one	O
could	O
append	O
modprobe.blacklist	O
=	O
nvidia-current	O
at	O
the	O
end	O
of	O
the	O
kernel	B-Operating_System
parameters	O
.	O
</s>
<s>
By	O
pressing	O
,	O
the	O
user	O
enters	O
the	O
GRUB	B-Application
command	O
line	O
.	O
</s>
<s>
The	O
GRUB	B-Application
command	O
line	O
is	O
not	O
a	O
regular	O
Linux	B-Application
shell	O
,	O
like	O
e.g.	O
</s>
<s>
bash	B-Operating_System
,	O
and	O
accepts	O
only	O
certain	O
GRUB-specific	O
commands	O
,	O
documented	O
by	O
various	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
Once	O
boot	O
options	O
have	O
been	O
selected	O
,	O
GRUB	B-Application
loads	O
the	O
selected	O
kernel	B-Operating_System
into	O
memory	O
and	O
passes	O
control	O
to	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
Alternatively	O
,	O
GRUB	B-Application
can	O
pass	O
control	O
of	O
the	O
boot	O
process	O
to	O
another	O
boot	B-Application
loader	I-Application
,	O
using	O
chain	B-Operating_System
loading	I-Operating_System
.	O
</s>
<s>
This	O
is	O
the	O
method	O
used	O
to	O
load	O
operating	B-General_Concept
systems	I-General_Concept
that	O
do	O
not	O
support	O
the	O
Multiboot	O
Specification	O
or	O
are	O
not	O
supported	O
directly	O
by	O
GRUB	B-Application
.	O
</s>
<s>
Each	O
time	O
the	O
computer	O
POSTs	B-Device
,	O
the	O
hard	O
disk	O
connected	O
to	O
port	O
1	O
(	O
of	O
the	O
motherboard	O
)	O
,	O
could	O
be	O
assigned	O
the	O
same	O
identifier	O
,	O
e.g.	O
</s>
<s>
By	O
entering	O
into	O
either	O
the	O
in	O
GRUB	B-Application
rescue	O
console	O
(	O
available	O
after	O
loading	O
core.img	O
)	O
or	O
the	O
GRUB	B-Application
console	O
(	O
available	O
after	O
loading	O
normal.mod	O
)	O
a	O
list	O
of	O
all	O
available	O
hard	O
disks	O
and	O
partitions	O
can	O
be	O
obtained	O
.	O
</s>
<s>
As	O
it	O
cannot	O
be	O
guaranteed	O
that	O
the	O
numbering	O
of	O
hard	O
disks	O
via	O
dumb	O
numbers	O
is	O
consistent	O
,	O
GNU	B-Application
GRUB	I-Application
can	O
use	O
the	O
UUID	O
to	O
identify	O
partitions	O
(	O
actually	O
file	B-Application
system	I-Application
instances	O
)	O
–	O
that	O
have	O
this	O
feature	O
–	O
instead	O
.	O
</s>
<s>
The	O
file	B-Application
systems	I-Application
ext2	O
,	O
ext3	O
,	O
ext4	B-Application
and	O
xfs	O
use	O
an	O
Universally	O
Unique	O
Identifier	O
(	O
UUID	O
)	O
to	O
uniquely	O
identify	O
an	O
instance	O
.	O
</s>
<s>
The	O
UUID	O
is	O
created	O
when	O
a	O
partition	O
is	O
formatted	B-Application
.	O
</s>
<s>
The	O
UUID	O
is	O
part	O
of	O
the	O
file	B-Application
system	I-Application
and	O
written	O
to	O
the	O
superblock	O
.	O
</s>
<s>
All	O
operations	O
but	O
a	O
formatting	O
should	O
leave	O
the	O
UUID	O
unaltered	O
,	O
but	O
it	O
is	O
possible	O
to	O
change	O
it	O
or	O
duplicate	O
it	O
(	O
by	O
using	O
dd	B-Application
to	O
clone	O
an	O
entire	O
partition	O
)	O
.	O
</s>
<s>
The	O
file	O
is	O
used	O
to	O
configure	O
GRUB	B-Application
.	O
</s>
<s>
Without	O
an	O
existing	O
and	O
valid	O
,	O
GRUB	B-Application
will	O
present	O
a	O
prompt	O
.	O
</s>
<s>
initial	B-Application
ramdisk	I-Application
)	O
:	O
</s>
<s>
GRUB	B-Application
was	O
initially	O
developed	O
by	O
Erich	O
Boleyn	O
as	O
part	O
of	O
work	O
on	O
booting	O
the	O
operating	B-General_Concept
system	I-General_Concept
GNU/Hurd	B-Application
,	O
developed	O
by	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
In	O
1999	O
,	O
Gordon	O
Matzigkeit	O
and	O
Yoshinori	O
K	O
.	O
Okuji	O
made	O
GRUB	B-Application
an	O
official	O
software	O
package	O
of	O
the	B-Application
GNU	I-Application
Project	I-Application
and	O
opened	O
the	O
development	O
process	O
to	O
the	O
public	O
.	O
</s>
<s>
,	O
the	O
majority	O
of	O
Linux	B-Application
distributions	I-Application
have	O
adopted	O
GNU	B-Operating_System
GRUB2	O
,	O
as	O
well	O
as	O
other	O
systems	O
such	O
as	O
Sony	O
's	O
PlayStation	O
4	O
.	O
</s>
<s>
GRUB	B-Application
version	O
1	O
(	O
also	O
known	O
as	O
"	O
GRUB	B-Application
Legacy	O
"	O
)	O
is	O
no	O
longer	O
under	O
development	O
and	O
is	O
being	O
phased	O
out	O
.	O
</s>
<s>
The	O
GNU	B-Application
GRUB	I-Application
developers	O
have	O
switched	O
their	O
focus	O
to	O
GRUB2	O
,	O
a	O
complete	O
rewrite	O
with	O
goals	O
including	O
making	O
GNU	B-Application
GRUB	I-Application
cleaner	O
,	O
more	O
robust	O
,	O
more	O
portable	O
and	O
more	O
powerful	O
.	O
</s>
<s>
GRUB2	O
started	O
under	O
the	O
name	O
PUPA	B-Application
.	O
</s>
<s>
PUPA	B-Application
was	O
supported	O
by	O
the	O
Information-technology	O
Promotion	O
Agency	O
(	O
IPA	O
)	O
in	O
Japan	O
.	O
</s>
<s>
PUPA	B-Application
was	O
integrated	O
into	O
GRUB2	O
development	O
around	O
2002	O
,	O
when	O
GRUB	B-Application
version	O
0.9x	O
was	O
renamed	O
GRUB	B-Application
Legacy	O
.	O
</s>
<s>
Some	O
of	O
the	O
goals	O
of	O
the	O
GRUB2	O
project	O
include	O
support	O
for	O
non-x86	O
platforms	B-Device
,	O
internationalization	B-General_Concept
and	I-General_Concept
localization	I-General_Concept
,	O
non-ASCII	O
characters	O
,	O
dynamic	O
modules	O
,	O
memory	B-General_Concept
management	I-General_Concept
,	O
a	O
scripting	O
mini-language	B-Language
,	O
migrating	O
platform	O
specific	O
(	O
x86	B-Operating_System
)	O
code	O
to	O
platform	O
specific	O
modules	O
,	O
and	O
an	O
object-oriented	O
framework	O
.	O
</s>
<s>
GNU	B-Application
GRUB	I-Application
version	O
2.00	O
was	O
officially	O
released	O
on	O
June	O
26	O
,	O
2012	O
.	O
</s>
<s>
Three	O
of	O
the	O
most	O
widely	O
used	O
Linux	B-Application
distributions	I-Application
use	O
GRUB2	O
as	O
their	O
mainstream	O
boot	B-Application
loader	I-Application
.	O
</s>
<s>
Ubuntu	B-Operating_System
adopted	O
it	O
as	O
the	O
default	O
boot	B-Application
loader	I-Application
in	O
its	O
9.10	O
version	O
of	O
October	O
2009	O
.	O
</s>
<s>
OpenSUSE	B-Operating_System
adopted	O
GRUB2	O
as	O
the	O
default	O
boot	B-Application
loader	I-Application
with	O
its	O
12.2	O
release	O
of	O
September	O
2012	O
.	O
</s>
<s>
Solaris	B-Application
also	O
adopted	O
GRUB	B-Application
2	I-Application
on	O
the	O
x86	B-Operating_System
platform	O
in	O
the	O
Solaris11.1	O
release	O
.	O
</s>
<s>
Also	O
Buildroot	B-Application
project	O
use	O
GNU	B-Application
GRUB	I-Application
for	O
x86	B-Operating_System
and	O
x86_64	B-Device
targets	O
.	O
</s>
<s>
GNU	B-Application
GRUB	I-Application
is	O
free	B-License
and	I-License
open-source	I-License
software	I-License
,	O
so	O
several	O
variants	O
have	O
been	O
created	O
.	O
</s>
<s>
Some	O
notable	O
ones	O
,	O
which	O
have	O
not	O
been	O
merged	O
into	O
GRUB	B-Application
mainline	O
:	O
</s>
<s>
OpenSolaris	B-Operating_System
includes	O
a	O
modified	O
GRUB	B-Application
Legacy	O
that	O
supports	O
Solaris	B-Application
VTOC	O
slices	O
,	O
automatic	O
64-bit	O
kernel	B-Operating_System
selection	O
,	O
and	O
booting	O
from	O
ZFS	B-Application
(	O
with	O
compression	B-General_Concept
and	O
multiple	O
boot	O
environments	O
)	O
.	O
</s>
<s>
Google	B-Application
Summer	I-Application
of	I-Application
Code	I-Application
2008	O
had	O
a	O
project	O
to	O
support	O
GRUB	B-Application
legacy	O
to	O
boot	O
from	O
ext4	B-Application
formatted	B-Application
partitions	O
.	O
</s>
<s>
The	O
Syllable	B-Application
project	O
made	O
a	O
modified	O
version	O
of	O
GRUB	B-Application
to	O
load	O
the	O
system	O
from	O
its	O
AtheOS	B-Application
File	I-Application
System	I-Application
.	O
</s>
<s>
TrustedGRUB	O
extends	O
GRUB	B-Application
by	O
implementing	O
verification	O
of	O
the	O
system	O
integrity	O
and	O
boot	O
process	O
security	O
,	O
using	O
the	O
Trusted	O
Platform	O
Module	O
(	O
TPM	O
)	O
.	O
</s>
<s>
The	O
Intel	O
BIOS	B-Operating_System
Implementation	O
Test	O
Suite	O
(	O
BITS	O
)	O
provides	O
a	O
GRUB	B-Application
environment	O
for	O
testing	O
BIOSes	O
and	O
in	O
particular	O
their	O
initialization	O
of	O
Intel	O
processors	O
,	O
hardware	O
,	O
and	O
technologies	O
.	O
</s>
<s>
BITS	O
supports	O
scripting	O
via	O
Python	O
,	O
and	O
includes	O
Python	O
APIs	O
to	O
access	O
various	O
low-level	O
functionality	O
of	O
the	O
hardware	B-Device
platform	I-Device
,	O
including	O
ACPI	O
,	O
CPU	O
and	O
chipset	O
registers	O
,	O
PCI	O
,	O
and	O
PCI	O
Express	O
.	O
</s>
<s>
GRUB4DOS	O
is	O
a	O
GRUB	B-Application
legacy	O
fork	O
that	O
improves	O
the	O
installation	O
experience	O
on	O
DOS	O
and	O
Microsoft	B-Application
Windows	I-Application
by	O
putting	O
everything	O
besides	O
the	O
GRLDR	O
config	O
in	O
one	O
image	O
file	O
.	O
</s>
<s>
It	O
can	O
be	O
loaded	O
directly	O
from	O
DOS	O
,	O
or	O
by	O
NTLDR	B-Application
or	O
Windows	B-Operating_System
Boot	I-Operating_System
Manager	I-Operating_System
.	O
</s>
<s>
GRUB4DOS	O
is	O
under	O
active	O
development	O
and	O
as	O
of	O
2021	O
supports	O
UEFI	B-Architecture
.	O
</s>
<s>
The	O
setup	O
tools	O
in	O
use	O
by	O
various	O
distributions	O
often	O
include	O
modules	O
to	O
set	O
up	O
GRUB	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
YaST2	B-Device
on	O
SUSE	O
Linux	B-Application
and	O
openSUSE	B-Operating_System
distributions	O
and	O
Anaconda	B-Language
on	O
Fedora/RHEL	O
distributions	O
.	O
</s>
<s>
StartUp-Manager	O
and	O
GRUB	B-Application
Customizer	O
are	O
graphical	O
configuration	O
editors	O
for	O
Debian-based	O
distributions	O
.	O
</s>
<s>
GRUB	B-Application
Customizer	O
is	O
also	O
available	O
for	O
Arch-based	O
distributions	O
.	O
</s>
<s>
Boot-Repair	O
is	O
a	O
simple	O
graphical	O
tool	O
for	O
recovering	O
from	O
frequent	O
boot-related	O
problems	O
with	O
GRUB	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
bootloader	B-Application
.	O
</s>
<s>
This	O
application	O
is	O
available	O
under	O
GNU	B-License
GPL	I-License
license	I-License
.	O
</s>
<s>
Boot-Repair	O
can	O
repair	O
GRUB	B-Application
on	O
multiple	O
Linux	B-Application
distributions	I-Application
including	O
,	O
but	O
not	O
limited	O
to	O
,	O
Debian	O
,	O
Ubuntu	B-Operating_System
,	O
Mint	B-Application
,	O
Fedora	O
,	O
openSUSE	B-Operating_System
,	O
and	O
Arch	O
Linux	B-Application
.	O
</s>
<s>
Grub2Win	O
is	O
a	O
Windows	B-Application
open-source	O
software	O
package	O
.	O
</s>
<s>
It	O
allows	O
GNU	B-Application
GRUB	I-Application
to	O
boot	O
from	O
a	O
Windows	B-Application
directory	O
.	O
</s>
<s>
The	O
setup	O
program	O
installs	O
GNU	B-Application
GRUB	I-Application
version	O
2.06	O
to	O
an	O
NTFS	O
partition	O
.	O
</s>
<s>
A	O
Windows	B-Application
GUI	O
application	O
is	O
then	O
used	O
to	O
customize	O
the	O
GRUB	B-Application
boot	O
menu	O
,	O
themes	O
,	O
UEFI	B-Architecture
boot	O
order	O
,	O
scripts	O
etc	O
.	O
</s>
<s>
All	O
GNU	B-Application
GRUB	I-Application
scripts	O
and	O
commands	O
are	O
supported	O
for	O
both	O
UEFI	B-Architecture
and	O
legacy	O
systems	O
.	O
</s>
<s>
Grub2Win	O
can	O
configure	O
GRUB	B-Application
for	O
multiboot	O
of	O
Windows	B-Application
,	O
Ubuntu	B-Operating_System
,	O
openSuse	B-Operating_System
,	O
Fedora	O
and	O
many	O
other	O
Linux	B-Application
distributions	I-Application
.	O
</s>
<s>
It	O
is	O
freely	O
available	O
under	O
GNU	B-License
GPL	I-License
License	I-License
at	O
SourceForge	O
.	O
</s>
<s>
The	O
strength	O
of	O
GRUB	B-Application
is	O
the	O
wide	O
range	O
of	O
supported	O
platforms	B-Device
,	O
file	B-Application
systems	I-Application
,	O
and	O
operating	B-General_Concept
systems	I-General_Concept
,	O
making	O
it	O
the	O
default	O
choice	O
for	O
distributions	O
and	O
embedded	O
systems	O
.	O
</s>
<s>
However	O
,	O
there	O
are	O
boot	B-Application
managers	I-Application
targeted	O
at	O
the	O
end	O
user	O
that	O
give	O
more	O
friendly	O
user	O
experience	O
,	O
graphical	O
OS	O
selector	O
and	O
simpler	O
configuration	O
:	O
</s>
<s>
rEFInd	B-Device
–	O
Macintosh-style	O
graphical	O
boot	B-Application
manager	I-Application
,	O
only	O
for	O
UEFI-based	O
computers	O
(	O
BIOS	B-Operating_System
not	O
supported	O
)	O
.	O
</s>
<s>
–	O
Macintosh-style	O
graphical	O
boot	B-Application
manager	I-Application
for	O
BIOS	B-Operating_System
and	O
UEFI-based	O
computers	O
.	O
</s>
<s>
It	O
emulates	O
UEFI	B-Architecture
with	O
a	O
heavily	O
modified	O
from	O
the	O
TianoCore	O
project	O
and	O
requires	O
a	O
FAT	O
formatted	B-Application
partition	O
even	O
on	O
BIOS	B-Operating_System
systems	O
.	O
</s>
<s>
As	O
a	O
benefit	O
,	O
it	O
has	O
a	O
basic	O
filesystem	B-Application
driver	O
in	O
the	O
partition	B-Device
boot	I-Device
sector	I-Device
,	O
avoiding	O
the	O
brittleness	O
of	O
a	O
second	O
or	O
third	O
stage	O
and	O
the	O
infamous	O
GRUB	B-Application
Rescue	O
prompt	O
.	O
</s>
<s>
The	O
user	O
interface	O
looks	O
similar	O
to	O
rEFInd	B-Device
:	O
both	O
inherit	O
from	O
the	O
abandoned	O
boot	B-Application
manager	I-Application
.	O
</s>
<s>
systemd-boot	B-Application
–	O
Light	O
,	O
UEFI-only	O
boot	B-Application
manager	I-Application
with	O
text-based	O
OS	O
selector	O
menu	O
.	O
</s>
