Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

curl > /dev/sda: How I made a Linux distro that runs wget | dd

astrid.tech

Post reply on HN
Print view View original

21–30 of 70 posts

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#21

Post by rkeene2 »

matja wrote: post #7

> How do you unmount your OS’s disk while keeping the OS running to be able to overwrite itself? I went down a similar rabbit-hole myself, with the goal of safely replacing the Linux installation on a disk that a machine is already running from (e.g. replace a VPS's setup image with one of your own) without needing a KVM-style remote access tool to the console. The problem there is if you directly modify the disk whe…

I usually just move all the files to a new directory (/oldroot) and pivot_root -- any open files reference the new paths. Then install into the newly empty root directory of the filesystem, reboot and delete the /oldroot.

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#22

Post by Joker_vD »

astralbijection wrote: post #20
Joker_vD wrote: post #6

Earlier quoted context omitted.

What if we remount the filesystem(s) at /dev/sda as read-only first? Then make a small ramfs with statically-linked curl in it and exec it. Hmm. Ideally, you'd also want to call reboot(2) after it's done...

All of those things get covered in parts 2, 3, and 4 :)

There's... no part 2 in the post? And it's the latest blog post on the site, as far as I can see.

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#23

Post by astralbijection »

Joker_vD wrote: post #22
astralbijection wrote: post #20

Earlier quoted context omitted.

All of those things get covered in parts 2, 3, and 4 :)

There's... no part 2 in the post? And it's the latest blog post on the site, as far as I can see.

It does get linked at the very bottom, though admittedly it could be made clearer. https://astrid.tech/2026/03/24/1/swap-out-the-root-before-bo...

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#24

Post by pzmarzly »

You will run into problems if destination drive has different sector size than your VM, as GPT header won't be aligned.

QEMU defaults to 512B sectors, which isn't true for many NVMe drives. There are some flags to change that. https://unix.stackexchange.com/a/722450

I think it should be possible to make an image with many headers at different locations, so that it works on all types of disks at once, but I don't think any tools do it for you by default.

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#25

Post by Joker_vD »

astralbijection wrote: post #23
Joker_vD wrote: post #22

Earlier quoted context omitted.

There's... no part 2 in the post? And it's the latest blog post on the site, as far as I can see.

It does get linked at the very bottom, though admittedly it could be made clearer. https://astrid.tech/2026/03/24/1/swap-out-the-root-before-bo...

Oh, I see, the posts got published in the reversed order.

On the topic itself: wow, what a journey. And I personally fully support "come on, you should totally be able to just dump the system image onto your disk and reboot/exec it!"

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#26

Post by ciupicri »

rwmj wrote: post #4

Unfortunately it's not safe as the kernel can still write to (what it thinks is) the old filesystem on the device, which will introduce corruption to the new disk image. However a fun fact is that you can (do not actually do this!) boot a qemu VM from /dev/sda. You have to use an overlay (eg. qemu -drive snapshot=on flag) so that qemu won't write through to /dev/sda. I use this trick in supernested, a script I wrote…

Could xfs_freeze help with this?

[0]: https://www.man7.org/linux/man-pages/man8/xfs_freeze.8.html

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#27

Post by astralbijection »

rwmj wrote: post #4

Unfortunately it's not safe as the kernel can still write to (what it thinks is) the old filesystem on the device, which will introduce corruption to the new disk image. However a fun fact is that you can (do not actually do this!) boot a qemu VM from /dev/sda. You have to use an overlay (eg. qemu -drive snapshot=on flag) so that qemu won't write through to /dev/sda. I use this trick in supernested, a script I wrote…

That script sounds extremely unhinged, and I mean it as a compliment :)

Without spoiling too much, the command at the very end of the series does something adjacent to this.

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#29

Post by BirAdam »

irishcoffee wrote: post #16

I've been dd-ing A/B partitions for embedded yocto distributions for years and years. read-only-rootfs (/var/log is its own writable partition), dd the "other partition", sed fstab, reboot. The neat part was the whole process kicked off when you scp'd the rootfs and inotifywait kicked off the whole process.

Yeah, make /home, /var/log, and /usr/local rw and everything else ro. Makes a great "immutable" that's not as annoying as truly "immutable" systems.

Re: curl > /dev/sda: How I made a Linux distro that runs wget | dd

#30

Post by tux3 »

rwmj wrote: post #4

Unfortunately it's not safe as the kernel can still write to (what it thinks is) the old filesystem on the device, which will introduce corruption to the new disk image. However a fun fact is that you can (do not actually do this!) boot a qemu VM from /dev/sda. You have to use an overlay (eg. qemu -drive snapshot=on flag) so that qemu won't write through to /dev/sda. I use this trick in supernested, a script I wrote…

I used to dual-boot windows, but I was too lazy to actually reboot, so naturally I had Virtualbox just boot the physical Windows partition while Linux was running. Which is totally fine!

It's not a real dual boot if you don't boot both partitions at the same time.

As long as you don't install guest VBox drivers, those would make it hang when it boots as the host on physical hardware, since there's no longer someone above to answer the hypercalls.

Post reply on HN