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The chroot Technique – a Swiss army multitool for Linux systems

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Re: The chroot Technique – a Swiss army multitool for Linux systems

#71

Post by messe »

thatcherc wrote: post #67
seba_dos1 wrote: post #3

With qemu-user and binfmt you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC to fix a hacking session gone wrong. Though these days you may want to look into things like systemd-nspawn instead of plain chroot.

> you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC This sounds very interesting! What's the scenario where you'd do this? Would you be, for example, emulating an ARM processor with qemu on an x86 computer and chrooting into Android on an eMMC?

I've done this on some tinker boards we use at work.

systemd-nspawn is a great tool for this.

Re: The chroot Technique – a Swiss army multitool for Linux systems

#72

Post by bitbang »

thatcherc wrote: post #67
seba_dos1 wrote: post #3

With qemu-user and binfmt you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC to fix a hacking session gone wrong. Though these days you may want to look into things like systemd-nspawn instead of plain chroot.

> you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC This sounds very interesting! What's the scenario where you'd do this? Would you be, for example, emulating an ARM processor with qemu on an x86 computer and chrooting into Android on an eMMC?

I've done this to build custom RPi images. Way faster than trying to build on a low power ARM platform, and way less fragile than cross compilers.

Re: The chroot Technique – a Swiss army multitool for Linux systems

#74

Post by benou »

thatcherc wrote: post #67
seba_dos1 wrote: post #3

With qemu-user and binfmt you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC to fix a hacking session gone wrong. Though these days you may want to look into things like systemd-nspawn instead of plain chroot.

> you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC This sounds very interesting! What's the scenario where you'd do this? Would you be, for example, emulating an ARM processor with qemu on an x86 computer and chrooting into Android on an eMMC?

Here is an example of preparing a debian ARM image on x86 with debootstrap, qemu and chroot:

  ~# sudo apt install qemu-user-static debootstrap
  ~# mkdir /tmp/arm
  ~# debootstrap --foreign --arch=armhf buster /tmp/arm http://deb.debian.org/debian
  ~# cp /usr/bin/qemu-arm-static /tmp/arm/usr/bin/
  ~# chroot /tmp/arm   # from that point, you're running ARM!
  ~# /debootstrap/debootstrap --second-stage

Re: The chroot Technique – a Swiss army multitool for Linux systems

#75

Post by nurettin »

jasongill wrote: post #63

This brings back memories - I owned a large web hosting company and we had thousands of machines. When hardware issues came up, or machines wouldn't boot, using this method was our first line of defense - we'd boot the machine from a burned copy of "Recovery Is Possible" which was an all-in-one Linux distro for recovery, then mount the partitions and chroot in to figure out what is going on - or use rsync to migrate…

Hetzner also chroots you into a recovery linux and mounts your drive for access. Same thing different scale.

Re: The chroot Technique – a Swiss army multitool for Linux systems

#76

Post by seba_dos1 »

thatcherc wrote: post #67
seba_dos1 wrote: post #3

With qemu-user and binfmt you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC to fix a hacking session gone wrong. Though these days you may want to look into things like systemd-nspawn instead of plain chroot.

> you can even chroot into foreign CPU architectures, which is a handy thing to have when you mount your phone's eMMC This sounds very interesting! What's the scenario where you'd do this? Would you be, for example, emulating an ARM processor with qemu on an x86 computer and chrooting into Android on an eMMC?

I used it with Debian on my phone, but yes.

Re: The chroot Technique – a Swiss army multitool for Linux systems

#77

Post by jimmaswell »

I just installed Gentoo from WSL2 this way, on my secondary NVME on my Framework 16. Went without a hitch besides some minor things you need to be aware of:

-the lack of access to efi subsystem from wsl means you need to pass some extra flags to help grub/etc along, and you may need to set it as the boot partition in the bios manually

-you'll have to mount the drive to wsl with `wsl --mount --bare`, after finding the right DiskPath with `Get-CimInstance -query "SELECT * from Win32_DiskDrive"`, and you might have to offline the disk first in Windows disk manager

Re: The chroot Technique – a Swiss army multitool for Linux systems

#78

Post by jimmaswell »

woleium wrote: post #70
jasongill wrote: post #63

This brings back memories - I owned a large web hosting company and we had thousands of machines. When hardware issues came up, or machines wouldn't boot, using this method was our first line of defense - we'd boot the machine from a burned copy of "Recovery Is Possible" which was an all-in-one Linux distro for recovery, then mount the partitions and chroot in to figure out what is going on - or use rsync to migrate…

System Rescue is what i use these days, but to be honest i can’t recall using it in the last couple of year. Virtualization and containers have taken over. https://www.system-rescue.org/

I use my Gentoo installation usb when this comes up

Re: The chroot Technique – a Swiss army multitool for Linux systems

#79

Post by anthk »

IshKebab wrote: post #66
dicroce wrote: post #4

I actually wish that instead of docker & etc we had just gotten a better chroot... Or maybe just a new kernel syscall that is chroot()++.

Plan9 had a proper solution for this. New processes don't get access to any files by default - you have to explicitly mount directories for them, capability style. Shame Plan9 blew its weirdness budget.

rfork it's easy :D

Re: The chroot Technique – a Swiss army multitool for Linux systems

#80

Post by _lvbh »

smallpipe wrote: post #2

The arch linux install has a little wrapper around chroot, used to configure the installed system without booting it. https://wiki.archlinux.org/title/Installation_guide#Chroot

I've actually used this to unbrick my laptop before. Very useful
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