Preparing a USB Memory Stick to boot the Installer

General instructions for creating a bootable USB device can be found in the installation-guide.

Here we also describe advanced methods for experienced users and special needs.

/!\ Be aware, that the methods described here will destroy anything already on the device! Make very sure that you use the correct device name for your USB stick. If you use the wrong device the result could be that all information on, for example, your hard disk is lost.

Method 1: Preparing a USB stick using a hybrid CD/DVD image

Debian installation images for this architecture are created using the isohybrid technology; that means they can be written directly to a USB stick, which is a very easy way to make an installation media. Simply choose an image (such as the netinst, CD or DVD-1) that will fit on your USB stick. An alternative for very small USB sticks, only a few megabytes in size, can be the mini.iso image from the netboot directory.

The image should be written directly to the USB stick, overwriting its current contents. For example, when using an existing GNU/Linux system, the image file can be written to a USB stick as follows, after having made sure that the stick is unmounted: 

# cp debian.iso /dev/sdX
# sync

/!\ The image must be written to the whole-disk device and not a partition, e.g. /dev/sdb and not /dev/sdb1. Do not use tools like unetbootin which alter the image.

Optional: Creating an additional partition for extra files

Simply writing the installation image to USB as described above should work fine for most users.

The hybrid image on the stick however does not occupy all the storage space, so it may be worth considering using the free space to hold firmware files or packages or any other files of your choice. This could be useful if you have only one stick or just want to keep everything you need on one device.

To do so, use cfdisk or any other partitioning tool to create an additional partition on the stick. Then create a (FAT) filesystem on the partition, mount it and copy or unpack the firmware onto it, for example with: 

# mkdosfs -n FIRMWARE /dev/sdX3
# mount /dev/sdX3 /mnt
# cd /mnt
# tar zxvf /path/to/firmware.tar.gz
# cd /
# umount /mnt

Take care that you use the correct device name for your USB stick. The mkdosfs command is contained in the dosfstools Debian package.

/!\ If you have chosen the mini.iso to be written to the USB stick, the second partition doesn't have to be created, as - very nicely - it has already be created. Unplugging and replugging the USB stick should make the two partitions visible.

Method 2: Manually copying files to the USB stick

Prior to isohybrid technology being used for Debian installation images, the methods documented below were used to prepare media for booting from USB devices. These have been superseded by the technique above in "Method 1", but have been kept for educational and historical purposes and in case they are useful to some user.

As an alternative to method 1 described above you can manually copy the installer files, and also an installation image to the stick. Note that the USB stick should be at least 1 GB in size (smaller setups are possible using the files from netboot, following the paragraph below).

There is an all-in-one file hd-media/boot.img.gz, which contains all the installer files (including the kernel) as well as syslinux and its configuration file.

/!\ Note that, although convenient, this method does have one major disadvantage: the logical size of the device will be limited to 1 GB, even if the capacity of the USB stick is larger. You will need to repartition the USB stick and create new file systems to get its full capacity back if you ever want to use it for some different purpose.

Simply extract this image directly to your USB stick: 

# zcat boot.img.gz > /dev/sdX

After that, mount the USB memory stick (mount /dev/sdX /mnt), which will now have a FAT filesystem on it, and copy a Debian ISO image (netinst or full CD) to it. Unmount the stick (umount /mnt) and you are done.

Method 3: Manually copying files to the USB stick — the flexible way

If you like more flexibility or just want to know what's going on, you should use the following method to put the files on your stick. One advantage of using this method is that — if the capacity of your USB stick is large enough — you have the option of copying any ISO image, even a DVD image, to it.

Partitioning and adding a boot loader

We will show how to set up the memory stick to use the first partition, instead of the entire device.

In order to start the kernel after booting from the USB stick, we will put a boot loader on the stick. Although any boot loader should work, it's convenient to use syslinux, since it uses a FAT16 partition and can be reconfigured by just editing a text file. Any operating system which supports the FAT file system can be used to make changes to the configuration of the boot loader.

First, you need to install the syslinux and mtools packages on your system.

Since most USB sticks come pre-configured with a single FAT16 partition, you probably won't have to repartition or reformat the stick. If you have to do that anyway, use cfdisk or any other partitioning tool to create a FAT16 partition now (don't forget to activate the “bootable” flag), and then install an MBR using: 

# cat /usr/lib/syslinux/mbr/mbr.bin >/dev/sdX

Now create the filesystem using: 

# mkdosfs /dev/sdX1

Take care that you use the correct device name for your USB stick. The mkdosfs command is contained in the dosfstools Debian package.

Having a correctly partitioned USB stick (now), you need to put syslinux on the FAT16 partition with: 

# syslinux /dev/sdX1

Again, take care that you use the correct device name. The partition must not be mounted when starting syslinux. This procedure writes a boot sector to the partition and creates the file ldlinux.sys which contains the boot loader code.

Adding the installer files

There are two different installation variants to choose here: The hd-media variant needs an installation ISO file on the stick, to load installer modules and the base system from. The netboot installer however will load all that from a Debian mirror.

According to your choice, you have to download some installer files from the hd-media or netboot subdirectory on any Debian mirror: 

vmlinuz or linux (kernel binary)
initrd.gz (initial ramdisk image)

You can choose between either the text-based version of the installer (the files can be found directly in hd-media or netboot) or the graphical version (look in the respective gtk subdirectories).

Then mount the partition (mount /dev/sdX1 /mnt) and copy the downloaded files to the root directory of the stick.

Next you should create a text file named syslinux.cfg in the root directory of the stick as configuration file for syslinux, which at a bare minimum should contain the following line: 

default vmlinuz initrd=initrd.gz

Change the name of the kernel binary to “linux” if you used files from netboot.

For the graphical installer (from gtk) you should add "vga=788" at the end of the line. Other parameters can be appended as desired.

To enable the boot prompt to permit further parameter appending, add the line 

prompt 1

If you used files from hd-media, you should now copy the ISO file of a Debian installation image onto the stick. (For the netboot variant this is not needed.) You can use either a netinst or a full CD/DVD image. Be sure to select one that fits on your stick. Note that the “netboot mini.iso” image is not usable for this purpose.

When you are done, unmount the USB memory stick (umount /mnt).

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