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本页介绍 如何创建并使用 Fedora 启动U盘。您可以使用一个 Fedora 启动U盘，在不安装 Fedora 系统到硬盘的情况下启动一台支持U盘启动的电脑。您可以在启动U盘中划分一块区域存储对系统的更改（安装软件或者修改配置），这种模式被称为 持续覆盖。您也可以划分一块单独空间用来存储用户账户信息和数据，比如文档和下载的文件，当然，为了数据安全您可以选择加密它们。总之，因为安装是非破坏性的，之前的文件和剩余的空间都可以在系统中访问。这相当于把整个电脑装在口袋里，在能找到的大部分机器上启动您自己的系统。

在现在的 Fedora 版本中，您也可以把非 Live 版本的 Fedora 镜像（DVD 和网络安装镜像）写入U盘，有些用户认为这样比写入光盘更快更方便。

快速开始
方法对大多数人都很简单。大多数厂商制造的U盘都适用。如果U盘中有文件，最好先备份一下。

重启电脑，选择计算机启动菜单的 USB 启动设备启动-- 通常是在启动时按下特定的键, 比如F12。 然后您可以开始试用了！！

如果您想获得技术上的细节，或者想获得更多关于可以选择的工具以及高级用法，请继续阅读下面的内容。
创建 Live CD ISO image
A Live USB system is created from the same ISO image file that is used to create Live CD/DVD media. You can download ISO images for the official Fedora release from the Fedora download site. Consult How to create and use a Live CD for more information on creating your own customized ISO image file.

系统需求

USB 引导启动功能

  • 鉴于不同的 BIOS 功能有所差别，部分电脑不能通过 USB 启动。如果您恰好在此列，考虑其他安装介质（光盘、硬盘等）。如果不确定是否能够通过 USB 启动，又不介意下载并刻录 Fedora 镜像至 USB 设备（可能会擦除您的数据），不妨一试，最多浪费一点时间。
  • U盘本身的问题也可能会造成失败，请注意错误信息。

GNU/Linux 方法

找到 USB

首先需要找出所在挂载点

  • 插入 USB
  • 打开终端，执行 dmesg。
  • 您将会看到类似下面的内容
[32656.573467] sd 8:0:0:0: [sdX] Attached SCSI removable disk

sdX 在您的电脑上可能是 sdb/sbc/sdd等等。记下这个标签，下文我们称之为 sdX。

检查USB容量

之前已经要求不得小于1GB。您可以通过执行 df -h 命令查看： 

/dev/sdX1             3.9G  4.0K  3.9G   1% /media/usbdisk

确保第一栏大于 1.0G。

您也可以使用比如 nautilus 右键查看磁盘属性：

写入镜像

图形方法：使用 liveusb-creator (仅 Windows/Fedora 可用)

Fedora USB sticks can be created using the liveusb-creator utility. Note that this utility is only capable of writing Live images.

You can use Add/Remove Programs and search for liveusb-creator, or use the command line: 

su -c 'yum install liveusb-creator'

To start, run liveusb-creator on the command line or search liveusb-creator on the GNOME activities overview.

To use the tool, simply select a Fedora release to download from the drop-down box at top-right (or select an ISO you have already downloaded using the Browse button at top-left), select the USB stick to which you wish to write the image from the Target Device drop-down box, and hit the Create Live USB button.

另一种启动方式：使用 Unetbootin

About Unetbootin
Following each release, Fedora support volunteers receive reports of problems with installation images created by Unetbootin. Using the most recent version of Unetbootin available has been known to improve results. While your results may vary, it is usually the case that the liveusb-creator, livecd-iso-to-disk and dd methods give better results than unetbootin. If you encounter problems with Unetbootin, please contact the Unetbootin developers, not the Fedora developers.

Unetbootin is a graphical bootable USB image creator. Using it will allow you to preserve any data you have in the USB drive.

  • Download Unetbootin latest version from http://unetbootin.sourceforge.net/ and install it.
  • You might have to type the root password when running it.
  • Click on Diskimage and search for the ISO file you downloaded.
  • Select Type: USB drive and choose sdX drive.
  • Press OK.
Note
If you do not see sdX listed, you might have to reformat the drive, effectively loosing all your data on the drive: 
su -c "umount /dev/sdX"
su -c "mkfs.vfat -I /dev/sdX"
.

Simple command line method: write the image directly

CAUTION
This will erase all data on the USB drive! Please read the instructions below carefully and make sure you write the right drive label (sdX).

To write the ISO file directly to the disk, run: 

su -c "dd if=/Users/me/Downloads/Fedora-17-x86_64-DVD.iso of=/dev/sdX bs=8M"

Or, if you are running an Ubuntu-based distribution 

sudo dd if=/Users/me/Downloads/Fedora-17-x86_64-DVD.iso of=/dev/sdX bs=8M

Note that the process will take some time and you will not see any information while it is running.

Command line method: Using the livecd-iso-to-disk tool (Fedora only)

The livecd-iso-to-disk is the most capable and often most reliable method of writing a Fedora ISO image to a USB stick, but can only reliably be used from within Fedora. It does not work in Windows and is not supported (and will usually fail) in non-Fedora distributions. Please use the liveusb-creator tool, dd (or an equivalent tool), or a third-party tool such as unetbootin on other operating systems. It is also not a good idea to try and write a new Fedora release using the version of livecd-iso-to-disk in a much older Fedora release: it is best to only use a release a maximum of two versions older than the release you are trying to write.

Make sure the livecd-tools RPM is installed with the command rpm -q livecd-tools. You will see the name of the RPM and a version number if it is installed, or no output if it is not installed.

If "livecd-tools" is not installed, install it using this command, or PackageKit: su -c 'yum install livecd-tools'

Detailed usage information is available in the first pages of the livecd-iso-to-disk script, which you can also see by running su -c 'livecd-iso-to-disk --help'. Basic examples follow.

To make an existing USB stick bootable as a Fedora image without deleting any of the data on it, make sure that the USB drive is not mounted before executing the following, and give the root password when prompted: su -c "livecd-iso-to-disk Fedora-17-x86_64-Live-Desktop.iso /dev/sdX"

See Data persistence below for how to create Live USB devices with more than temporary storage of user files and settings.

In case it is not possible to boot from a disk created with the method shown above, before re-partitioning and re-formatting, often resetting the master boot record will enable booting: su -c "livecd-iso-to-disk --reset-mbr Fedora-17-x86_64-Live-Desktop.iso /dev/sdX"

CAUTION
The following method will erase all data on the USB drive! Please read the instructions below carefully.

If necessary, you can have livecd-iso-to-disk re-partition and re-format the target stick: su -c "livecd-iso-to-disk --format --msdos --reset-mbr Fedora-17-x86_64-Live-Desktop.iso /dev/sdX"

UEFI boot of USB sticks

Whether a Fedora image written to a USB stick will be bootable natively via UEFI is a somewhat complex question which depends on the Fedora release, the type of image (live or non-live), and the method used to write it. The --efi parameter to the livecd-iso-to-disk tool attempts to make a stick written with that tool natively UEFI bootable.

As of Fedora 17, all images written using the dd method should be UEFI-bootable, and all images written with livecd-iso-to-disk --format --reset-mbr --efi should also be UEFI-bootable. Use of --efi without --format and --reset-mbr can be considered a 'best effort', and may not produce a UEFI-bootable stick.

Creating a USB stick from a running live environment

If you are already running a live CD, DVD, or USB and want to convert that into a bootable USB stick, run the following command: su -c "livecd-iso-to-disk /run/initramfs/livedev /dev/sdX"

(For versions before Fedora 17, use /dev/live instead of /run/initramfs/livedev.)

永久数据

Data persistence means that your files and settings will remain even after you reboot your live system. You can perform updates just like a regular installation to your hard disk, except that kernel updates require manual intervention and overlay space may be insufficient. The primary use of this feature is booting a USB stick with your live image as well as the persistent changes. Note that you will need to have space on your target USB stick for the live image plus your overlay plus any other data you want on the stick.

Use the Graphical Method described above to do this easily. There is a graphical slider in the interface you can use to assign space on the target stick for persistent storage.

If using the livecd-iso-to-disk tool, add the --overlay-size-mb parameter to add a persistent data storage area to the target stick. For example: su -c "livecd-iso-to-disk --overlay-size-mb 512 Fedora-16-x86_64-Live-Desktop.iso /dev/USBPARTITIONNAME"

where 512 is the desired size (in megabytes) of the overlay. The livecd-iso-to-disk tool will not accept an overlay size value greater than 2047 for VFAT, but for ext[234] filesystems it is only limited by the available space.

Limited Lifetime of Persistent Overlay
One very important note about using the "primary" persistent overlay for system changes is that due to the way it's currently implemented (as a Device-mapper copy-on-write snapshot), every single change to it (writes AND deletes) subtracts from its free space, so it will eventually be "used up" and your USB stick will no longer boot (see this dm-devel discussion and this page for emergency recovery). Because of these limitations, it is advisable to use the system-level persistence sparingly, for configuration changes and important security updates only. Or, if you have sufficient disk space available, changes to the LiveOS root filesystem snapshot can be merged into a new copy of the root filesystem. See this page section for instructions.

See this section for mounting the root filesystem outside of a boot.

For normal, write-many storage (vs the write-once overlay), use the --home-size-mb option to create a home directory filesystem for personal files. The home.img can be re-used and loop mounted outside of the Live USB environment.

The persistent overlay status may be queried by issuing this command on the live system: dmsetup status live-rw

The returned value may look like this: 

live-rw: 0 8388608 snapshot 42296/204800 176

where the fraction after 'snapshot' for the logical volume is that of 512-byte sectors consumed in the overlay.

Windows 下方法

Using liveusb-creator

Fedora USB sticks can be created using the liveusb-creator utility. Note that this utility is only capable of writing Live images.

  • Download liveusb-creator from the site
  • Double click liveusb-creator

To use the tool, simply select a Fedora release to download from the drop-down box at top-right (or select an ISO you have already downloaded using the Browse button at top-left), select the USB stick to which you wish to write the image from the Target Device drop-down box, and hit the Create Live USB button.

Booting the image

Set USB as first boot device. Your BIOS may be different.
  • Power off the computer.
  • Plug the USB drive into a USB port.
  • Remove all other portable media, such as CD, DVD, or floppy disks.
  • Power on the computer.
  • If the computer is configured to automatically boot off of the USB drive, you will see a screen that says "Automatic boot in 10 seconds..." with a countdown.
  • If the computer starts to boot off the hard drive, you'll need to manually configure it to boot off the USB drive.
    • Wait for a safe point to reboot safely.
    • As the machine starts to reboot, watch carefully for instructions on which key to press (usually a function key or Escape) to enter the boot device selection menu, or "BIOS setup". Press and hold that key. If you miss the window of opportunity (often only a few seconds) then reboot and try again.
    • Use the BIOS setup menu to put your USB drive first in the boot sequence. It might be listed as a hard drive rather than a removable drive. Each hardware manufacturer has a slightly different method for doing so. Use caution! Your computer could become unbootable or lose functionality if you change any other settings. Though these settings can be reverted, you'll need to remember what you changed in order to do so.
    • Save the changes, exit, and the computer should boot the Live USB drive.

问题解答

liveusb-creator problems

Partition isn't marked bootable!

If you get the following message, you need to mark the partition bootable. 

$ su -c "livecd-iso-to-disk Fedora-1-x86_64-Live-Desktop.iso /dev/sdX"
Partition isn't marked bootable!
You can mark the partition as bootable with 
    $ /sbin/parted /dev/sdX
    (parted) toggle N boot
    (parted) quit
Cleaning up to exit...

To mark the partition bootable, run parted, and use the 'toggle X boot' command. For example: 

$ parted /dev/sdX
GNU Parted 1.8.6
Using /dev/sdX
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print                                                            
Model: Imation Flash Drive (scsi)
Disk /dev/sdX: 1062MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      32.3kB  1062MB  1062MB  primary  fat16             

(parted) toggle 1 boot
(parted) print                                                    
Model: Imation Flash Drive (scsi)
Disk /dev/sdX: 1062MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      32.3kB  1062MB  1062MB  primary  fat16        boot 

(parted) quit                                                             
Information: Don't forget to update /etc/fstab, if necessary.

Partitions need a filesystem label!

If you get the following message, you need to label the partition. 

$ su -c "livecd-iso-to-disk Fedora-16-x86_64-Live-Desktop.iso /dev/sdX"
Need to have a filesystem label or UUID for your USB device
Label can be set with /sbin/dosfslabel
Cleaning up to exit...

To label the partition: 

su -c "dosfslabel /dev/sdX LIVE"

Partition has different physical/logical endings!

If you get this message from fdisk, you may need to reformat the flash drive, as described earlier in this guide.

MBR appears to be blank!

If your test boot reports a corrupted boot sector, or you get the following message, you need to install or reset the master boot record (MBR). 

$ su -c "livecd-iso-to-disk Fedora-17-x86_64-Live-Desktop.iso /dev/sdX"
MBR appears to be blank.
You can add an MBR to this device with
Cleaning up to exit...

To install or reset MBR: 

$ su -c "livecd-iso-to-disk --reset-mbr Fedora-17-x86_64-Live-Desktop.iso /dev/sdX"

Issues using other Linux distributions

Ubuntu and derivative Linux distributions have a usb-creator program similar to Live USB Creator. This does not work with Fedora ISO images, it silently rejects them. usb-creator requires the ISO to have a Debian layout, with a /.disk/info file and a casper directory. Do not attempt to use this utility to write a Fedora ISO image.

The livecd-iso-to-disk script is not meant to be run from a non-Fedora system. Even if it happens to run and write a stick apparently successfully from some other distribution, the stick may well fail to boot. Use of livecd-iso-to-disk on any distribution other than Fedora is unsupported and not expected to work: please use an alternative method, such as dd described above.

Testing Live Image on USB

You can test your Live Image on USB using QEMU as shown in the screenshot below.

For example, you could type the following commands: 

su -c 'umount /dev/sdX1'
qemu -hda /dev/sdX -m 1024 -vga std

Mounting a Live USB filesystem

You can use the liveimage-mount script in the livecd-tools package to mount an attached Live USB device or other LiveOS image, such as an ISO or Live CD. This is convenient when you want to copy in or out some file from the LiveOS filesystem on a Live USB, or just examine the files in a Live.iso or Live CD.

Kernel updates

If you have sufficient overlay space to accommodate a kernel update on a Live USB installation, the kernel and initramfs will be installed to the /boot directory. To put these into service they must be moved to the /syslinux directory of the installation partition. This is accessible from the running Live USB filesystem at either the /mnt/live or /run/initramfs/live mount point. The new initramfs (such as initramfs-3.3.2-6.fc16.x86_64.img) and kernel (such as vmlinuz-3.3.2-6.fc16.x86_64) should be moved to replace the /mnt/live/syslinux/initrd0.img and /mnt/live/syslinux/vmlinuz0 files, respectively.

  • Note: Beginning with Fedora 17 and updated Fedora 16, dracut no longer includes the dmsquash-live module by default. So one should include it in /etc/dracut.conf with, for example,
    # echo 'add_dracutmodules+=" dmsquash-live "' >> /etc/dracut.conf

The following commands will move the new kernel and initramfs files and create symbolic links to them, in case one later wants to perform a full install of the image to a hard disk. 

bootpath=run/initramfs/live/syslinux
# bootpath=mnt/live/syslinux
new=3.3.2-6.fc16.x86_64

cd /
mv -f boot/vmlinuz-$new ${bootpath}/vmlinuz0
mv -f boot/initramfs-${new}.img ${bootpath}/initrd0.img
 
ln -fs -T ../${bootpath}/vmlinuz0 boot/vmlinuz-$new
ln -fs -T ../${bootpath}/initrd0.img boot/initramfs-${new}.img

您也可以参考

Red Hat Magazine | I am Fedora, and so can you!

参考

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