2014
02.26

this article is gentoo centric but can be done with most other distro’s pretty easily.

i did this with a 4gb flash disk, but size is not an issue depending on what you plan on putting on there.

First things first, lets make sure you have all the needed tools:

emerge sys-fs/dosfstools
which can be grabbed from here as source or just check your package manager for dosfstools

once we have that, lets partition and format the flash drive:

just wipe the disk and create a new partition (this was done using fdisk):

Welcome to fdisk (util-linux 2.24.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15610576896 bytes, 30489408 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Device    Boot Start       End   Blocks  Id System
/dev/sdb1 *     8064  30489407 15240672  af HFS / HFS+

Command (m for help): d

Selected partition 1
Partition 1 has been deleted.

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15610576896 bytes, 30489408 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Command (m for help): n

Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-30489407, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-30489407, default 30489407): 

Created a new partition 1 of type 'Linux' and of size 14.6 GiB.

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15610576896 bytes, 30489408 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Device    Boot Start       End   Blocks  Id System
/dev/sdb1       2048  30489407 15243680  83 Linux

now lets change the type:

Command (m for help): t

Selected partition 1
Hex code (type L to list all codes): L

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris        
 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     85  Linux extended  c7  Syrinx         
 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data    
 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility   
 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt         
 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access     
 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O        
 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor      
 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi eb  BeOS fs        
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         ee  GPT            
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ef  EFI (FAT-12/16/
10  OPUS            55  EZ-Drive        a7  NeXTSTEP        f0  Linux/PA-RISC b
11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f1  SpeedStor      
12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f4  SpeedStor      
14  Hidden FAT16 <3 61  SpeedStor       ab  Darwin boot     f2  DOS secondary  
16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      fb  VMware VMFS    
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE 
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fe  LANstep        
1c  Hidden W95 FAT3 75  PC/IX           be  Solaris boot    ff  BBT            
1e  Hidden W95 FAT1 80  Old Minix      
Hex code (type L to list all codes): c
If you have created or modified any DOS 6.x partitions, please see the fdisk documentation for additional information.
Changed type of partition 'Linux' to 'W95 FAT32 (LBA)'.

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15610576896 bytes, 30489408 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Device    Boot Start       End   Blocks  Id System
/dev/sdb1       2048  30489407 15243680   c W95 FAT32 (LBA)

lets make it bootable:

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15610576896 bytes, 30489408 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc3072e18

Device    Boot Start       End   Blocks  Id System
/dev/sdb1       2048  30489407 15243680   c W95 FAT32 (LBA)

Command (m for help): a

Selected partition 1
The bootable flag on partition 1 is enabled now.

now save and exit:

Command (m for help): w

The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

after you are done with that, lets format the disk:
% sudo mkfs.vfat /dev/sdb1

and now, lets mount the drive and install grub2 on it:

% sudo mount /dev/sdb1 /usb
% sudo grub2-install --no-floppy --root-directory=/usb /dev/sdb
Installing for i386-pc platform.
Installation finished. No error reported.

now you may notice that on the flash disk there is a folder named "boot", we are also going to create a folder named "iso" where we are going to actually keep the iso images as shown in the grub.cfg below:
% mkdir /usb/iso

now that the hard part is done, we need to add a grub.cfg file & start placing iso's on this disk.
at the time of writing, these are the iso's i had on my boot disk:
Debian netinst 7.4.0 amd64
Gentoo minimal 20140220 amd64
Gentoo minimal 20140211 i386
Kali Linux 1.0.6 amd64
Ubuntu 13.10 amd64

vi /usb/boot/grub/grub.cfg

contents of my grub.cfg (change to suit your needs):

set timeout=30
set default=0
set menu_color_normal=white/black
set menu_color_highlight=white/green

# boot isos
menuentry "Debian netinst 7.4.0 64bit" {
  set isofile="/iso/debian-7.4.0-amd64-netinst.iso"
  set bootoptions="vga=normal --"
  loopback loop $isofile
  linux (loop)/install.amd/vmlinuz $bootoptions
  initrd (loop)/install.amd/initrd.gz
}

menuentry "Gentoo minimal 20140220 64bit" {
  set isofile="/iso/install-amd64-minimal-20140220.iso"
  set bootoptions="root=/dev/ram0 init=/linuxrc nokeymap cdroot cdboot looptype=squashfs loop=/image.squashfs initrd=gentoo.igz usbcore.autosuspend=1 console=tty0 rootdelay=10 isoboot=$isofile"
  loopback loop $isofile
  linux (loop)/isolinux/gentoo $bootoptions
  initrd (loop)/isolinux/gentoo.igz
}

menuentry "Gentoo minimal 20140211 32bit" {
  set isofile="/iso/install-x86-minimal-20140211.iso"
  set bootoptions="root=/dev/ram0 init=/linuxrc nokeymap cdroot cdboot looptype=squashfs loop=/image.squashfs initrd=gentoo.igz usbcore.autosuspend=1 console=tty0 rootdelay=10 isoboot=$isofile"
  loopback loop $isofile
  linux (loop)/isolinux/gentoo $bootoptions
  initrd (loop)/isolinux/gentoo.igz
}

menuentry "Kali Linux 1.0.6 64bit" {
  set isofile="/iso/kali-1.0.6_64.iso"
  bootoptions="findiso=$isofile boot=live noconfig=sudo username=root hostname=kali quiet splash"
  search --set -f $isofile
  loopback loop $isofile
  linux (loop)/live/vmlinuz $bootoptions
  initrd (loop)/live/initrd.img
}

menuentry "Ubuntu 13.10 64bit" {
  set gfxpayload=keep
  set isofile="/iso/ubuntu-13.10-desktop-amd64.iso"
  set bootoptions="-- quiet"
  loopback loop $isofile
  linux (loop)/linux $bootoptions
  initrd (loop)/initrd.gz
}
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charlie root

VP of keeping it real / HNIC at pissedoffadmins.com
I bring the cold coffee.

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