Gentoo Archives: gentoo-user

From: Grant Edwards <grant.b.edwards@×××××.com>
To: gentoo-user@l.g.o
Subject: [gentoo-user] Re: [OT] Making a bootable USB flash drive from ISO image
Date: Thu, 02 Oct 2014 21:39:12
Message-Id: m0kgks$gtg$1@ger.gmane.org
In Reply to: Re: [gentoo-user] [OT] Making a bootable USB flash drive from ISO image by Neil Bothwick
1 On 2014-10-02, Neil Bothwick <neil@××××××××××.uk> wrote:
2 > On Thu, 2 Oct 2014 21:11:03 +0000 (UTC), Grant Edwards wrote:
3 >
4 >> What I'm wondering is why all the blog posts, wiki pages, and HOWTOs
5 >> showing either the complicated command-line procedures or
6 >> dependency-heavy "USB creator" apps? (Many of them quite recent.)
7 >
8 > There is no need for them.
9
10 >> Did this work because the Xubuntu people do something special when
11 >> creating the ISO image? (If so, then they have my thanks!)
12 >
13 > They did something, but it's not particularly special. All they did was
14 > run isohybrid (from syslinux) on the ISO image. It uses unused space at
15 > the start of the DVD ISO specification that is normally left blank to
16 > hold a partition table so the image can be copied to a USB drive and
17 > appear as a partitioned disk.
18
19 There must be a little more to it than that. Does it also install
20 along with a parition table some bootloader code that knows where/how
21 to boot the ISO boot image? [After a little googling] It also
22 installs MBR bootloader code that knows how to find/load isolinux.bin:
23
24 http://www.syslinux.org/wiki/index.php/Isohybrid
25
26 Interestingly, it also created a second EFI boot partition which
27 exists inside the main parition.
28
29 $ sudo fdisk -l /dev/sdd
30
31 Disk /dev/sdd: 7.3 GiB, 7864320000 bytes, 15360000 sectors
32 Units: sectors of 1 * 512 = 512 bytes
33 Sector size (logical/physical): 512 bytes / 512 bytes
34 I/O size (minimum/optimal): 512 bytes / 512 bytes
35 Disklabel type: dos
36 Disk identifier: 0x19fabbe1
37
38 Device Boot Start End Blocks Id System
39 /dev/sdd1 * 0 1904639 952320 0 Empty
40 /dev/sdd2 14296 18967 2336 ef EFI (FAT-12/16/32)
41
42 I can mount the sdd2 VFAT partition, and there are a couple files
43 in there:
44
45 sdd2
46 └── efi
47 └── boot
48 ├── bootx64.efi
49 └── grubx64.efi
50
51 --
52 Grant Edwards grant.b.edwards Yow! SHHHH!! I hear SIX
53 at TATTOOED TRUCK-DRIVERS
54 gmail.com tossing ENGINE BLOCKS into
55 empty OIL DRUMS ...

Replies

Subject Author
Re: [gentoo-user] Re: [OT] Making a bootable USB flash drive from ISO image Neil Bothwick <neil@××××××××××.uk>