brent s. <bts@square-r00t.net> 于2019年11月6日周三 上午10:42写道：
On 11/5/19 9:11 PM, Hongyi Zhao via arch-general wrote:
$ sudo ddrescue -f archlinux-2019.11.01-x86_64.iso /dev/sdc2 The ISO contains multiple partitions, so probably not.
Why when using the whole usb disk, the problem will disappear?
As both Eli and I have both explained, because if you use the whole disk you're writing a partition table as *the partition table for the device*. If you try to write to a partition, you end up with nested partition tables. The .iso file is a *disk image*, not a *partition image*.
Why are you trying to do this, precisely?
I want to use a usb disk for installation of multiple distros, say, Debian, Ubuntu, Arch, and so on. In this case, I must not using the whole usb disk for only one iso, and on the other hand, using whole usb disk for only one iso, is wasting of the usb's space, considering that we cannot use it for doing other things. Furthermore, I noticed that the dd-based method is more robust than using the iso directly with grub's loopback module.
In what way?
See the following partition method and settings on my usb stick: werner@debian-01:~$ sudo sfdisk -l /dev/sdc Disk /dev/sdc: 114.6 GiB, 123010547712 bytes, 240254976 sectors Disk model: Ultra USB 3.0 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: gpt Disk identifier: BB18A52C-1382-4003-B6CF-CE137E913145 Device Start End Sectors Size Type /dev/sdc1 2048 6143 4096 2M BIOS boot /dev/sdc2 6144 210943 204800 100M EFI System /dev/sdc3 210944 164050943 163840000 78.1G Linux filesystem /dev/sdc4 188954624 191002623 2048000 1000M Linux filesystem /dev/sdc5 191002624 199194623 8192000 3.9G Linux filesystem /dev/sdc6 199194624 213530623 14336000 6.9G Linux filesystem /dev/sdc7 213530624 215578623 2048000 1000M Linux filesystem /dev/sdc8 215578624 218650623 3072000 1.5G Linux filesystem /dev/sdc9 218650624 223361023 4710400 2.3G Linux filesystem /dev/sdc10 223361024 234010623 10649600 5.1G Microsoft basic data Some explains: sdc1: bios_grub for grub booting with gpt sdc2: EFI diretory sdc3: boot diretory sdc4- : dd-based iso images
I do not agree with this. It's far easier to update the ISO, it's far easier to add new distributions to the bootloader (and both updating and adding new entries can even be done by regular users without granting disk reformatting permissions), etc. with grub loopback.
To say the least, for the Debian iso, the dd-based method can do the trick while the loopback method will fail to detect the cd-rom during the installation progress.
Are you using the appropriate kernel cmdline args in the menu entry? They're different from Arch's grub loopback menu entry.
https://wiki.debian.org/DebianLive/MultibootISO
Alternatively, you can use grub to boot an ISO *file* as a loopback device. Some people do this to create multiboot USBs.
As I said above, this method is not so robust as the dd-based method. In detail, the most robust method for using the usb disk to installation a unix/linux OS, should be the dd-based method which using the whole usb disk. But this method has the shortcoming that it will occupy the whole usb disk with only a small iso image and prohibit us for using the usb disk to do other things at the same time.
This seems highly subjective. What makes using DD superior to a loopback? It occupies the same exact disk space as if you dd'd to a partition except requires no modifications to the host disk.
Now, if you *really* want to save space, you'd extract the squashed filesystems/initrds/kernels from each ISO you want to add and create grub entries that boot those directly, but that only affords you a couple extra megabytes per distribution. However, *that is not what grub loopback is*. Grub boots an iso file *directly*, with no modifications required. I guarantee it's far more maintainable and robust than any use of dd.
-- brent saner https://square-r00t.net/ GPG info: https://square-r00t.net/gpg-info
-- Hongsheng Zhao <hongyi.zhao@gmail.com> Institute of Semiconductors, Chinese Academy of Sciences GnuPG DSA: 0xD108493