byteback - maintenance-free client & server backup scripts for Linux ==================================================================== byteback encapsulates Bytemark's "best practice" for maintenance-free backups with easy client and server setup. "Maintenance-free" means that we'd rather make full use of a fixed amount of disc space. Management of disc space must be completely automatic, so the process never grinds to a halt for reasons that could be automatically resolved. Failed backups can be restarted in case of network problems. We use the standard OpenSSH on the server for encrypted transport & access control, btrfs for simple snapshots and rsync for efficient data transfer across the network. Backups should require as little configuration as possible to be safe - just the server address should be enough. Setting up: server ------------------ Install the 'byteback' package on the server, along with its dependencies (rsync, sudo). You then need to perform the following local setup on the server, which can securely handle backups for multiple clients. You need a dedicated user (which is usually called 'byteback') with a home directory on a btrfs filesystem, and some privileges to run commands through sudo. The following commands are appropriate for a Debian system, you might need to alter it for other Linux distributions, or if you are not using LVM for your discs: # Create a dedicated UNIX user which will store everyone's backups, and # allow logins # adduser --system byteback --home /byteback --shell /bin/bash # Allow the backup user to run the snapshot command # # echo </etc/sudoers.d/byteback byteback ALL = (root) NOPASSWD: /usr/local/bin/byteback-snapshot byteback ALL = (root) NOPASSWD: /usr/bin/byteback-snapshot byteback ALL = (root) NOPASSWD: /sbin/btrfs subvolume create Defaults:byteback !requiretty SUDOERS # Create a dedicated btrfs filesystem for the user, and add that as its home # lvcreate my_volume_group --name byteback --size 1000GB mkfs.btrfs /dev/my_volume_group/byteback echo '/dev/my_volume_group/byteback /byteback btrfs compress 0 0' >>/etc/fstab mount /byteback Finally, before setting up the client, add PermitUserEnvironment yes to /etc/ssh/sshd_config, and restart sshd. Setting up: client ------------------ Clients are machines that need to be backed up. Assuming you can log into the remote 'byteback' user with a password or administrative key, you only need to type one command on the client to set things going: byteback-setup-client --destination byteback@mybackuphost.net: If this goes OK, you are ready to start backing up. I'd advise taking the first backup manually to make sure it goes as you expect. Type this on the client to start and watch the backup. byteback-backup --verbose Configuring byteback-backup --------------------------- You can now set "byteback-backup" on a daily cron job to start backing up the server on a regular basis. Without any further options this will copy every file from the root downwards. It currently excludes /tmp, /var/tmp, /var/cache/apt/archives, /swap.file and /var/backups/localhost which (on Bytemark systems) do not need to be part of any backup. To specify which locations are excluded, add them to /etc/byteback/excludes, one per line. The filesystems /dev, /proc, /run and /sys are always excluded. It is possible to configure a full rsync filter by creating the file /etc/byteback/rsync_filter, which is parsed to rsync via the --filter flag. Note that excludes on the command line take precedence, unless the filter starts with an exclamation mark, which resets everything. If you do this, you'll need to specify /proc, /sys, etc manually. See the rsync manpage for more information about filters. When the backup has completed successfully, the server will take a snapshot so that the client can't alter the backups, and then "prune" the backup snapshots to ensure that the next backup is likely to run OK. If the backup is interrupted or dies unexpected, running "byteback backup" will cause the backup to be resumed, with rsync saving the work of re-copying any files that hadn't changed. By default this will happen automatically up to 5 times, with a 10 minute pause in between each attempt. Viewing and restoring backups ----------------------------- Backups can be viewed on the server filesystem, although the permissions will be wrong. The rsync "fake-super" flag is used to store the permissions in a user attribute list. To view this list on the server, run getfaddr -d $filename This command is part of the "attr" package in Debian. To restore a file to the current directory, you need to run: rsync -Prat --rsync-path='rsync --fake-super' byteback@mybackuphost.net:path/to/file . The --fake-super flag only applies to the "local" end, hence the need to specfy the rsync-path. You'll need to set up correct SSH permissions at the remote end for this to work. The trust model --------------- Backups are intended to keep your data safe, and byteback makes the assumption that the client may become hostile to the backup server. At Bytemark this allows us to guard against rogue employees of our clients destroying the backup, while ensuring that our clients can still access all their old backups. There are several measures to guard against this, though they are all ineffective over a long enough period of time: * the server uses SSH's command feature to ensure that clients can only run rsync to the appropriate directory; * the server's snapshots are read-only, so the client can't just rsync an empty directory over an old backup; * the server will refuse to take snapshots "too often" to stop the client from filling the disc with useless data; * the server will refuse to prune away space for a new backup that is suddenly larger than previous ones. Pruning behaviour ----------------- Unless you are backing up a very small amount of data, backups will always need pruning, i.e. old backups must be deleted to make way for newer ones. There is a program on the server called byteback-prune which deals with this operation. It deletes old backups until a certain amount of free space is achieved, which is currently determined to be the average size of the last 10 backups, plus 50%. It can choose which backups to delete by one of two methods: 1) the 'age' method simply deletes the oldest backup; 2) the 'importance' method tries to retain a more spread-out backup pattern by "scoring" each backup according to how close it is to a set of "target times". These are 0, 1, 2, 3, 7, 14, 21, 28, 56, and 112 days. So when you ask the pruner to run, the backup closest to the present time will be the last one to be deleted. The backup closes to "1 day ago" will be the second-last, and so on. We score every backup in this way until we end up with a "least important" snapshot to delete. The upshot of the second strategy should be that we retain closely-spaced daily backups, but as they get too numerous, we make sure that we are reluctant to delete our very oldest. [TODO: model it]