Autobackup

Automatic incremental backups using rsync

Autobackup allows you to create incremental backups on specific hard drives, as soon as they are connected to the system. It is based completely on standard linux tools.

Incremental backups

With rsync, it is possible to create hard links to files, if they already exist in another directory. This allows to track changes in big directory structures, without the necessity to create independent copies of the full database each time. backup.sh provides a tool for that. You can remove (rm) older versions of your data anytime, without affecting the other copies, since the linux filesystem does not actually overwrite any files as long as at least one hard link exists to them.

Automatic execution

If one of your backup drives is connected to the system, this is detected by a udev rule (80-backup.rules). udev then starts a systemd unit (autobackup@.service) in the background, which calls autobackup.sh to perform the backup. autobackup.sh mounts the hard drive using the name given from udev, makes a backup of your folders using backup.sh and unmounts the drive afterwards.

Installation

• It is best if you deactivate the automounting for the drives. Therefore, make an entry like UUID=29af023f-df9f-48ee-aced-61ffbdaba804 /mnt/autobackup1 auto noauto 0 0 in /etc/fstab. You can find the UUID from ll /dev/disk/by-uuid/.
• You need to register your drive to be mounted in 80-backup.rules by providing a set of unique attributes to this piece of hardware, e.g. the serial number, the vendor or the device type. You can find available attributes by using the command

udevadm info -a -n /dev/sda

Afterwards, execute install.sh as root. The backup will be executed as root as well and the drive mounted as read only for non-root users

• All configurations are done via a autobackup.conf file. The location of this file needs to be specified at the top of the autobackup.sh script.

Configuration

The directories to be backed up are defined via a file autobackup.conf. You can place it anywhere, as long as you specify the location at the beginning of the autobackup.sh script.

LUKSKEY=/path/to/lukskey
/path/to/dir1
/path/to/dir2

Backups

They are started once you plug in the drive. You can monitor the progress via the logfile in /tmp/autobackup.log. Once finished, the drive is automatically unmounted. You can power it of before plugging out via

udisksctl power-off -b /dev/sda1

Restore Backups

If not encrypted, the backups are directly readable as normal files on the drives. On any other computer, they should be mounted normally. Since on this computer, the automounting is deactivated, you have to mount the plate manually. After the backup finished, you can remount the plate using the following commands:

mkdir /mnt/backup_to_read
sudo mount -o ro /dev/sda1 /mnt/backup_to_read #instead of sda1, use the name which is printed after the backup finished. -o ro: read only mount
#after you are finished:
sudo umount /mnt/backup_to_read
udisksctl power-off -b /dev/sda1

Encryption

Optionally, you can encrypt the external drive e.g. using LUKS. To prepare the hard drive, follow this manual: https://wiki.ubuntuusers.de/LUKS/Partitionen_verschl%C3%BCsseln/ To open the drive, autobackup.sh expects a keyfile to use with cryptsetup luksOpen --key-file .... The location of the key file can be configured via the autobackup.conf file. In the udev rule, you need to switch the drive type from 'normal' to 'encrypted'.

Inspiration

This project was inspired by the following webpages:

• https://www.sanitarium.net/golug/rsync_backups_2010.html
• https://www.admin-magazine.com/Articles/Using-rsync-for-Backups