4.3. Forberedning af filer for opstart via USB-hukommelsesdrev

To prepare the USB stick, we recommend to use 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 lsblk before and after inserting it. (The output of dmesg (as root) is another possible method for that.) To write to your stick, you may have to turn off its write protection switch.

[Advarsel] Advarsel

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 is lost.

4.3.1. 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. See Afsnit 4.1, “Official Debian GNU/Linux installation images” to get an installation image.

Alternativt kan du for meget små USB-drev på kun nogle få megabyte hente aftrykket mini.iso fra mappen netboot (på placeringen nævnt i Afsnit 4.2.1, “Where to Find Installation Files”).

The installation image you choose 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

Information about how to do this on other operating systems can be found in the Debian CD FAQ.

[Vigtigt] Vigtigt

Aftrykket skal skrives til whole-disk-enheden og ikke en partition, f.eks. /dev/sdb og ikke 7dev/sdb1. Brug ikke værktøjer såsom unetbootin som ændrer aftrykket.

[Vigtigt] Vigtigt

Simply writing the installation image to USB like this should work fine for most users. The other options below are more complex, mainly for people with specialised needs.

Hybridaftrykket på drevet bruger ikke al lagerplads, så kan være en overvejelse værd at bruge den ledige plads til firmware-filer eller pakker eller andre filer efter dit eget valg. Dette kan være nyttigt, hvis du kun har et drev eller bare ønsker at have alt på en enhed.

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.

[Bemærk] Bemærk

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 will already be present. Unplugging and replugging the USB stick should make the two partitions visible.

4.3.2. Manuelt kopiere filer til USB-drevet

Prior to isohybrid technology being used for Debian installation images, the methods documented in the chapters below were used to prepare media for booting from USB devices. These have been superseded by the technique in Afsnit 4.3.1, “Preparing a USB stick using a hybrid CD/DVD image”, but have been left here for educational and historical purposes and in case they are useful to some user.

An alternative to the method described in Afsnit 4.3.1, “Preparing a USB stick using a hybrid CD/DVD image” is to 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 Afsnit 4.3.3, “Manuelt kopiere filer til USB-drevet — den fleksible måde”).

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.

[Bemærk] Bemærk

Bemærk dog, selvom det er nemt, at denne metode har en stor ulempe: Den logiske størrelse på enheden vil være begrænset til 1 GB, selv hvis kapaciteten på USB-drevet er større. Du skal partitionere USB-drevet igen og oprette nye filsystemer for at få den fulde kapacitet tilbage, hvis du ønsker at bruge den til andre formål.

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; see Afsnit 4.1, “Official Debian GNU/Linux installation images”) to it. Unmount the stick (umount /mnt) and you are done.

4.3.3. Manuelt kopiere filer til USB-drevet — den fleksible måde

Hvis du ønsker højere fleksibilitet eller bare ønsker at vide, hvad der foregår, så kan du bruge en af de følgende metoder til at placere filerne på dit drev. En af fordelene ved denne metode er at — hvis kapaciteten på dit USB-drev er stor nok — så kan du kopiere ethvert ISO-aftryk eller endda et dvd-aftryk til drevet. Partitioning and adding a boot loader

Vi vil vise hvordan hukommelsesdrevet opsættes til at bruge den første partition, i stedet for hele enheden.

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.

[Bemærk] Bemærk

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[3], and then install an MBR using:

# cat /usr/lib/syslinux/mbr/mbr.bin 

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 of debian/dists/bullseye/main/installer-i386/current/images/ 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.

For at aktivere opstartsprompten til at acceptere yderligere parametertilføjelse, tilføjes en linje 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 (see Afsnit 4.1, “Official Debian GNU/Linux installation images”). 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).

[3] Don't forget to activate the bootable flag.