stillron / just-so

Use BTRFS snapshots to reset public computers to known state after reboot

JustSo

BTRFS-based snapshots provide automatic rollbacks of user home folders.

Setup

Debian

• Start the setup process by Selecting Advanced Options > Expert Install

• Go through:

  • Language
  • Keyboard
  • Detect installation media
  • Load Installer components
  • Detect Network Hardware
  • Configure the Network
  • Setup users and passwords (lebtech)
  • Configure the clock
  • Detect disks

• Then, at Partition disks create new GPT partition

Create EFI Partition

• Go down to FREE SPACE and press enter to create the first (EFI) partition.
• Choose Create a new partition
• Enter 1 GB for size and select Beginning for position of partition.
• On the next screen, choose Use as and select EFI System Partition
• Choose Done from menu

Create Swap Partition

• Go down to FREE SPACE again to setup swap partition.
• Choose Create a new partition
• Make size 1.5 x Amount of RAM on the machine and select Beginning for position of partition.
• On the next screen, choose Use as and select Swap area
• Choose Done from menu

Create BTRFS partition

• Go down to FREE SPACE again to setup BTRFS partition.
• Choose Create a new partition
• Leave size at remaining space available.
• On the next screen, choose Use as and select btrfs journaling filesystem
• Choose Done

Writing out the partitions to disk

• Arrow down to Finish partitioning and write changes to disk and press enter.
• Answer Yes to all prompts

Setting up initial subvolumes

DO NOT CONTINUE TO NEXT STEP in installer (yet).

• Instead press CTRL+ALT+F2 to get a terminal window.

• Enter df command to see which partitions are mounted at:

/target
/target/boot/efi

• umount the two above partitions.

• mount whatever partition was previously mounted to /target to /mnt

• cd to /mnt

• rename root snapshot from @rootfs to @

• mount the root subvolume to target with:

mount -o rw,noatime,compress=zstd:1,space_cache=v2,subvol=@ /dev/<root partition> /target

• create efi directories to mount to inside of /target

mkdir -p /target/boot/efi

• Mount /boot/efi with

mount /dev/<boot partition> /target/boot/efi

Updating /etc/fstab

Now we need to reflect our recent changes in fstab. Use nano to edit /target/etc/fstab

The lines for / and should look like the following:

UUID=<(NO CHANGE NEEDED)> /  btrfs   rw,noatime,compress=zstd:1,space_cache=v2,subvol=@   0 0

Return to installer

All manual updates are now done. Return to installer by typing exit in the command line and then entering CTRL+ALT+F1

Continue through the rest of the installation process.

Usage

Note: justso must be run with admin privileges*

• # justso init Sets up the initial environment for justso.
• # justso make <profile> Creates a user and corresponding home directory.
• # justso enable <profile> Enables rolling back of user profile on reboot.
• # justso disable <profile> Stop rolling back user's home directory upon reboot.
• # justso pin <profile> Creates new snapshot of user's home directory.
• # justso back <profile> Rolls the user's home directory back to the latest snapshot.
• # justso unpin <profile> [Num snapshots] Removes the latest n snapshots (defaults to 1).
• # justso revert <profile> [Num snapshots] Unpins n number of snapshots and rolls back to latest surviving snapshot.
• # justso prune <profile> [Num snapshots] Removes n number of oldest snapshots.
• # justso send [-i | --incremental ] <profile> Creates a backup file of the latest snapshot that can be sent to other devices for import.
• # justso receive <profile> <path to exported btrfs file> Import a file of a btrfs snapshot into the profile's snapshot folder to be used on next reboot.
• (TODO) # justso destroy <profile> Completely removes a profile.
• (TODO) # justso status <profile> Provides information about the status of user's profile.