It was also actually pretty fun!
Give me more of this and less of the politics. This is what I come to Lemmy for.
Impressive, sounds like magic, tbh! You know any tutorials?
Not really, I pulled it together from a bunch of random posts lol
Maybe I should write one, but in essence you:
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Stop all non-OS essential services
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Create a filesystem in a chunk of RAM
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Pull essential OS files from the installed OS into it recreating needed directories (Though you could probably just use a tiny pre-built distro but meh)
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Pivot root into it
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Reload services (when they restart they’ll be restarted in the context of where you pivot rooted, prior they’re still running under the context of the installed OS)
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Unmount the boot drive
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Then do what ever you need to do
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???
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Profit
chroot isn’t enough, you need “real” pivot_root
chroot just changes the shells root point, pivot_root actually changes the root mount point and enables this trick to work
The man page has a good example.
Yeah, I’d love to see a write up on this to follow.Sounds like useful practice in the lab if nothing else.
i experimented with this some time ago, see my post here: https://lemmy.ml/post/18706002/12772832
What happens if the SSH session closes before dd finishes? Sounds pretty badass but I don’t think I would trust this approach in prod lol
Well the 1 SSH session bit was for dramatic meme-effect lol, you can actually connect back without issue (at least it did for me) so worst case if you weren’t working in tmux you’d just have to start dd again
Worst worst case, you’d just end up back where you were probably heading before anyways, KVM/IPMI
I also vote for a writeup. This sounds awesome!
Can someone ELI5? Are you freefloating an operating system on your RAM?
I had a server I rented from a provider in a data center and I wanted to image (dd) the drive for archival before I decommissioned it from my infrastructure.
Normally, you can’t really do that with the OS running and you would have to shut down and insert a live USB or something and temporarily boot from that. The server being a faraway rental the only option was to open a ticket so that they could enable an out-of-band management option like KVM or IPMI. Which would allow you to control a machine as if you had a physical monitor, keyboard and mouse in front of you. With that you can attach flash drives, shutdown, restart, see the POST/BIOS/UEFI screens etc remotely .
But, I didn’t want to wait 6-8 hours for them to enable that so instead I put together a process that would “boot” me into another distro “installed” into a RAM disk (kinda like how live CD/USB works) from the currently installed and running OS without rebooting
From there I could unmount the boot disk and do what ever I wanted from there, I could have even wiped the disk entirely and installed a entirely different distro if I wanted
RAM is still memory, so you can put anything in there, like an OS.
With pivot_root, you can change where the root is. So you pivot into your OS in RAM, which becomes the root of the system.
At that point, you can do pretty much anything you would normally do with your OS, like unmount a HDD.
I’ve never personally done it, but that’s a simplified explanation of what OP did.
