# Linux Recovery with Live USB and Chroot
Today, my Linux system crashed unexpectedly.

My dual-boot system has a habit of imploding when Windows updates it's boot
config. When my graphic adapter and wifi stop working, I am left with a mostly
inoperable system.

Rather than reinstall Ubuntu all over and wreck all my configuration, I
prefer to attempt a recovery using a live USB.

The system can't start because we needed to update the boot partition, but 
we didn't get the updates done before something crashed the system (or the OS
refused to boot). Or something else is terribly wrong.

Whatever the cause, a lot of the times a `apt upgrade` or `dnf update`
is all a system needs, but there is no easy way to get there with a dorked
boot partition.

## Tutorial

### Live USB
You'll need to find a 4GB USB drive (Hopefully USB 3.0).

When repairing my dual-boot, I'll use my operable Windows installation to prepare
a live boot USB if I don't have one on hand.

When making a bootable Linux USB on Windows, the tool to use is Rufus.

[Rufus](https://rufus.ie/)

Tutorial on making a live USB on Windows with Rufus from Canonical:

[Create a bootable USB stick with Rufus on Windows](https://ubuntu.com/tutorials/create-a-usb-stick-on-windows)

### Boot from USB to the Live system
How to do this step varies for each computer. Usually mashing f12 works on
Dell computers.

Select "Try or Install" when GRUB asks you what you want to do next.

Another pop up in the GUI will probably ask you this question again.
Select "Try" to start the live environment. If you have a live distro
that is only CLI, that's fine too!

What you are looking for here is a way to get to a shell prompt with working
drivers.

### Prepare to Chroot
Our goal is to hand the reigns of our functioning system to the root of the filesystem that we are struggling to boot.

The Archlinux Wiki has a great article about using `chroot`:

[chroot-ArchWiki](https://wiki.archlinux.org/title/chroot#Usage)

Begin with making directories to mount your chroot environment onto:
```
$ sudo -i
# mkdir /rescue
# cd /rescue
```
To start, let's find our root (`/`) filesystem. This system is likely to be fine, but we can't boot far enough to utilize it to it's full potential.

Try `ls /dev` and `fdisk` to find the root to your linux system. Mine is
a ext4 filesystem that lives on `/dev/sdb4`.

To mount the `/` onto our chroot environment:
```
# mount /dev/sdb4 /rescue/
```

Next, we need to figure out where the dorked boot partition lives. Since we
are on a live system, our current `/boot` isn't what we want our `chroot` to
effect. 

I use a combination of `ls /dev` and `fdisk` to identify the dorked partition.

Let's hand our dorked `/boot` to the a mountpoint at `/rescue/boot/`

```
# mkdir /rescue/boot
# mount /dev/sda3 /rescue/boot/
```

Next, we want to hand over access to `proc` and `sys` this passes through PIDs
and system device settings:

```
# mkdir /rescue/{proc,sys}
# mount -t proc /proc proc/
# mount -t sysfs /sys sys/
```

Now, we bind mount `/dev` and `/run`:

```
# mkdir /rescue/{dev,run}
# mount -o bind/dev dev/
# mount -o bind/run run/
```

If you are doing this on an EFI boot system, you'll want to
bind mount your EFI variables. This important for fixing boot related
issues on EFI.

```
# mount -o bind /sys/firmware/efi/efivars sys/firmware/efi/efivars/
```

### Chroot into /rescue
Finally, the moment of truth. `chroot` into `/rescue`:
```
# chroot /rescue
```
If your prompt just changed, you've done something right! I am dropped
into a `bash` shell as `root`, and when I `ls /home` I see that I
am where I belong.

Anything we do in this sub-shell will act upon our dorked `/boot` and root
directory.

### Hope this fixes it!
Cross our fingers, and run:

```
# apt update && apt upgrade -y
```

For good measure, double down on building initramfs:
```
# depmod -a
# update-initramfs -u
```

### Exit chroot
Type `exit` to leave the `chroot` environment. 

### Unmount directories 
`cd` to home, and unmount all those `/rescue` directories:

```
# umount --recursive /rescue
```

### Reboot

```
# shutdown -r now
```
## Alternatives
If you managed to update the chroot enironment, but your system still doesn't
boot, you have the tools you need to recover files from your broken system
before reinstalling your Linux distribution.

* Boot into the Live environment
* Stash whatever you need from the old root filesystem
* Blow all of the problems away with a fresh system install. 

I usually consider distro hopping when this happens, but I prefer Ubuntu for a
dual-boot with Windows because its installer makes safely installing Ubuntu simple.