4.3. Preparing Files for USB Memory Stick Booting

There are two installation methods possible when booting from USB stick. The first is to install completely from the network. The second is to also copy a CD image onto the USB stick and use that as a source for packages, possibly in combination with a mirror. This second method is the more common.

For the first installation method you'll need to download an installer image from the netboot directory (at the location mentioned in Section 4.2.1, “Where to Find Installation Images”) and use the “flexible way” explained below to copy the files to the USB stick.

Installation images for the second installation method can be found in the hd-media directory and either the “easy way” or the “flexible way” can be used to copy the image to the USB stick. For this installation method you will also need to download a CD image. The installation image and the CD image must be based on the same release of debian-installer. If they do not match you are likely to get errors[6] during the installation.

To prepare the USB stick, you will need a system where GNU/Linux is already running and where USB is supported. With current GNU/Linux systems the USB stick should be automatically recognized when you insert it. If it is not you should check that the usb-storage kernel module is loaded. When the USB stick is inserted, it will be mapped to a device named /dev/sdX, where the “X” is a letter in the range a-z. You should be able to see to which device the USB stick was mapped by running the command dmesg after inserting it. To write to your stick, you may have to turn off its write protection switch.

Warning

The procedures described in this section 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 a hard disk could be lost.

Note that the USB stick should be at least 256 MB in size (smaller setups are possible if you follow Section 4.3.2, “Copying the files — the flexible way”).

4.3.1. Copying the files — the easy way

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 256 MB, 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. A second disadvantage is that you cannot copy a full CD image onto the USB stick, but only the smaller businesscard or netinst CD images.

To use this image simply extract it 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 netinst or businesscard ISO image to it. Unmount the stick (umount /mnt) and you are done.

4.3.2. Copying the files — 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 a full CD ISO image to it.

4.3.2.1. Partitioning the USB stick

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

Note

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[7], and then 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.

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 (e.g. lilo) 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.

To put syslinux on the FAT16 partition on your USB stick, install the syslinux and mtools packages on your system, and do:

# 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.

4.3.2.2. Adding the installer image

Mount the partition (mount /dev/sdX1 /mnt) and copy the following installer image files to the stick:

  • vmlinuz or linux (kernel binary)

  • initrd.gz (initial ramdisk image)

You can choose between either the regular version or the graphical version of the installer. The latter can be found in the gtk subdirectory. If you want to rename the files, please note that syslinux can only process DOS (8.3) file names.

Next you should create a syslinux.cfg configuration file, which at a bare minimum should contain the following two lines (change the name of the kernel binary to “linux” if you used a netboot image):

default vmlinuz
append initrd=initrd.gz

For the graphical installer you should add video=vesa:ywrap,mtrr vga=788 to the second line.

If you used an hd-media image, you should now copy a Debian ISO image[8] onto the stick. When you are done, unmount the USB memory stick (umount /mnt).

4.3.3. Booting the USB stick

Warning

If your system refuses to boot from the memory stick, the stick may contain an invalid master boot record (MBR). To fix this, use the install-mbr command from the package mbr:

# install-mbr /dev/sdX



[6] The error message that is most likely to be displayed is that no kernel modules can be found. This means that the version of the kernel module udebs included on the CD image is different from the version of the running kernel.

[7] Don't forget to set the “bootable” bootable flag.

[8] You can use either a businesscard, a netinst or a full CD image (see Section 4.1, “Official Debian GNU/Linux CD-ROM Sets”). Be sure to select one that fits. Note that the “netboot mini.iso” image is not usable for this purpose.