We want to restore a Linux installation, that is, its

• root / and
• home /home/$USER directory

onto another computer.

Premises

We assume that the installed Linux system (in our case, it happened to be openSUSE 42.2) uses

• the bootloader grub2

and has separate partitions for

• the root / and
• the home /home folders

As a backup tool, we will use rsync, because it is

• stable,
• fast
• versatile, and
• free of dependencies, that is, it is a single executable.

Saving the Installation

First, while not strictly necessary, copying the rsync executable, say /usr/bin/rsync into the $BKP_FOLDER by

cp /usr/bin/rsync $BKP_FOLDER

avoids depending on whether rsync has been installed on the rescue system or not.

To save the partitions:

1. Use lsblk to identify the backup partition: its device letter, say b, and its partition number, say 1; for example /dev/sdb1.

2. Mount the partition $PARTITION to a folder $FOLDER, say /mnt, by mount $PARTIION $FOLDER, say mount /dev/sdb1 /mnt:

    MOUNT=/mnt
    BKP_LABEL=USB_BKP
   
    BKP_MOUNT="$MOUNT"/"$BKP_LABEL"
    mkdir --parents "$BKP_MOUNT"
    mount /dev/sdb1 "$BKP_MOUNT"
   

3. Copy

   • the home partition, skipping trash and cache files, and

   • the root partition, skipping the home folder (which is on a separate partition) and folders that only contain

     • boot images and kernel modules,
     • backups
     • removable media, and
     • temporary and cache files:

    BKP_FOLDER="$BKP_MOUNT"
   
    HOME_FOLDER="/home/$USER"
    HOME_BACKUP_FOLDER="$BKP_FOLDER/home"
    mkdir --parents "$HOME_BACKUP_FOLDER"
   
    rsync -avxEHA --delete --human-readable --info=progress2 \
      --exclude="/.local/share/Trash" \
      --exclude="/.cache" \
      "$HOME_FOLDER/" "$HOME_BACKUP_FOLDER/"
   
    ROOT_FOLDER="/"
    ROOT_BACKUP_FOLDER="$BKP_FOLDER/root"
    mkdir --parents "$BKP_FOLDER/root"
   
    rsync -avxEHA --delete --human-readable --info=progress2 \
      --exclude=/home \
      --exclude='/etc/fstab' \
      --exclude='/boot/' \
      --exclude='/lib/' \
      --exclude='/lib64/' \
      --exclude='/.snapshots' \
      --exclude='/media' \
      --exclude='/mnt' \
      --exclude='/run' \
      --exclude='/dev' \
      --exclude='/proc' \
      --exclude='/sys' \
      --exclude='/tmp' \
      --exclude='/var/run' \
      --exclude='/var/lock' \
      --exclude='/var/tmp' \
      "$ROOT_FOLDER" "$ROOT_BACKUP_FOLDER/"
   
    umount --verbose "$BKP_MOUNT"
    rmdir --verbose "$BKP_MOUNT"
   

Restoring the installation

To restore the installation,

1. reinstall Linux minimally,
2. copy the partitions, and
3. finally restore the bootloader:

Reinstalling Linux

1. To

   • partition the hard drive, and
   • install the bootloader (Grub2 in our case),

   install the Linux distribution in its most basic configuration (that is, installing as few packages as possible).

2. Once Linux is installed, boot into a rescue system, such as that on the installation medium (DVD or USB drive) of the Linux distribution.
3. Log into a terminal.
4. Use ls -l /dev/disk/by-uuid to detect which device letter (say /dev/sda) is assigned to which hard disk and which number to which partition.

5. Note the letter and number of the

   • backup partition, as well as
   • the root and home partitions.

   (For example, /dev/sda might be the hard disk, \dev\sda2 the root partition and \dev\sda3 the home partition).

Restoring the partitions

We assume that

• the backup partition is /dev/sdb2, and
• the root and home partitions are /dev/sda2 and /dev/sda3.

To first mount and then restore the files:

mkdir -p /mnt/bkp && mount /dev/sdb2 /mnt/bkp

(
cd /mnt/bkp/

mkdir -p /mnt/root && mount /dev/sda2 /mnt/root
rsync \
  --info=stats1,progress2 --human-readable --compress \
  --archive --executability --hard-links --modify-window=1 --acls --xattrs \
  --update --delete \
  --exclude='/home' \
  --exclude='/.snapshots' \
  --exclude='/media' \
  --exclude='/mnt' \
  --exclude='/run' \
  --exclude='/dev' \
  --exclude='/proc' \
  --exclude='/sys' \
  --exclude='/tmp' \
  --exclude='/var/run' \
  --exclude='/var/lock' \
  --exclude='/var/tmp' \
  ./ /mnt/root/

mkdir -p /mnt/home && mount /dev/sda3 /mnt/home
rsync \
  --info=stats1,progress2 --human-readable --compress \
  --archive --executability --hard-links --modify-window=1 --acls --xattrs \
  --update --delete \
  ./home/ /mnt/home/
)

Restoring the bootloader

We assume (as above) that the root partition is /dev/sda1. To restore the bootloader:

mkdir -p /mnt/root && mount /dev/sda2 -t btrfs /mnt;

mount /dev/sda2 -o subvol=/@/boot/grub2/x86_64-efi  /mnt/boot/grub2/x86_64-efi;
mount /dev/sda2 -o subvol=/@/boot/grub2/i386-pc     /mnt/boot/grub2/i386-pc;
mount /dev/sda2 -o subvol=/@/var                    /mnt/var;
mount /dev/sda2 -o subvol=/@/usr/local              /mnt/usr/local;
mount /dev/sda2 -o subvol=/@/tmp                    /mnt/tmp;
mount /dev/sda2 -o subvol=/@/srv                    /mnt/srv;
mount /dev/sda2 -o subvol=/@/root                   /mnt/root;
mount /dev/sda2 -o subvol=/@/opt                    /mnt/opt;

mkdir -p /mnt/root/dev && mount --bind /dev      /mnt/root/dev
chroot /mnt/root
  mkdir -p /mnt/root/proc && mount -t proc  proc  /proc
  mkdir -p /mnt/root/sys  && mount -t sysfs sysfs /sys

  grub2-mkconfig -o /boot/grub2/grub.cfg && grub2-install /dev/sda
exit