brent s. <bts@xxxxxxxxxxxxxxx> 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@xxxxxxxxx> Institute of Semiconductors, Chinese Academy of Sciences GnuPG DSA: 0xD108493
