Given that the "volume" lines in the btrbk configuration file are valid mount-points, you can loop through the configuration and mount the volumes like this:
#!/bin/sh
btrbk list volume --format=raw | while read line; do
eval $line
$volume_rsh mount $volume_path
done
Note that the btrbk list command accepts filters (see btrbk(1),
FILTER STATEMENTS), which means you can e.g. add "group automount"
tags in your configuration and dump only the volumes of this group:
btrbk list volume automount.
Create a file /etc/apt/apt.conf.d/70btrbk, e.g.:
// create a btrfs snapshot before (un)installing packages
Dpkg::Pre-Invoke {"/usr/bin/btrbk run /mnt/btr_pool/rootfs";};
In order to make sure that the snapshots are always generated and
nothing is deleted, add the btrbk command line options --preserve --override=snapshot_create=always.
Referring to a btrbk configuration like this:
volume /
subvolume .
snapshot_name rootfs
Btrbk is designed to operate on the subvolumes within a root subvolume. In the config above, the btrbk snapshots would be created inside the source subvolume, altering it (from user perspective). From btrfs perspective this is not a problem, as the snapshots are separate subvolumes referring to the source subvolume and mapped into the file system tree below the source subvolume.
The recommended way is to split your data into subvolumes, e.g.:
# btrfs subvolume create /mnt/data/www
# btrfs subvolume create /mnt/data/mysql
# btrfs subvolume create /mnt/data/projectx
This way you make full advantage of the btrfs filesystem, as all your data now has a name, which helps organizing things a lot. This gets even more important as soon as you start snapshotting and send/receiving.
The btrbk configuration for this would be:
volume /mnt/data
subvolume www
[...]
subvolume mysql
[...]
subvolume projectx
[...]
There's lots of ways to do this, and each one of them has its reason to exist. Make sure to read the btrfs SysadminGuide on kernel.org as a good entry point.
If your linux root filesystem is btrfs, I recommend booting linux from
a btrfs subvolume, and use the btrfs root only as a container for
subvolumes (i.e. NOT booting from "subvolid=5"). This has the big
advantage that you can choose the subvolume in which to boot by simply
switching the rootflags=subvol=<subvolume> kernel boot option.
Example (/boot/grub/grub.cfg):
menuentry 'Linux' {
linux /boot/vmlinuz root=/dev/sdb3 ro rootflags=subvol=rootfs quiet
}
menuentry 'Linux (testing)' {
linux /boot/vmlinuz root=/dev/sdb3 ro rootflags=subvol=rootfs_testing
}
Note that btrbk snapshots and backups are read-only, this means you have to create a run-time (rw) snapshot before booting into it:
# btrfs subvolume snapshot /mnt/btr_pool/backup/btrbk/rootfs-20150101 /mnt/btr_pool/rootfs_testing
There's several ways to achieve this, the solution described below guarantees not to create new files (extents) on disk.
Assuming that '/' is mounted with subvolid=5:
# btrfs subvolume snapshot / /rootfs
Note that this command does NOT make any physical copy of the files of your subvolumes within "/", it will only add some metadata.
Add mount point for subvolid=5 to fstab, something like this:
/rootfs/etc/fstab:
/dev/sda1 /mnt/btr_pool btrfs subvolid=5,noatime 0 0
This step is not critical for a proper root change, but will save your time by preventing further configurations/reboots and manually mounting the toplevel subvolume.
Either add rootflags=subvol=rootfs to grub.cfg, or set subvolume
"rootfs" as default:
# btrfs subvolume set-default <subvolid> /
You can obtain <subvolid> via
btrfs subvolume show /rootfs | grep "Subvolume ID"
Editing grub.cfg manually may lead you some troubles if you perform some actions that will fire
grub-mkconfig.
First check your system log for btrfs errors:
cat /var/log/messages | grep -i btrfs | grep -i error
then check if current / is our new subvolume:
# btrfs subvolume show /
Name: rootfs
...
Great, this tells us that we just booted into our new snapshot!
# btrfs subvolume show /mnt/btr_pool
/mnt/btr_pool is toplevel subvolume
This means that the root volume (subvolid=5) is correctly mounted.
Carefully delete all old files from /mnt/btr_pool, except "rootfs"
and any other subvolumes within "/mnt/btr_pool". In other words,
delete any folders that are NOT LISTED by btrfs subvolume list -a /mnt/btr_pool:
# cd /mnt/btr_pool
# mkdir TO_BE_REMOVED
# mv bin sbin usr lib var ... TO_BE_REMOVED
Then reboot. If everything went fine, remove the directory:
# cd /mnt/btr_pool
# rm -rf TO_BE_REMOVED
It is very common (and avisable!) to keep backups on a separate location. In some situations, it is also required to transport the data physically, either to the datacenter or to your safe in the basement.
A robust approach is to use external disks as archives (secondary backups), and regularly run "btrbk archive" on them. As a nice side effect, this also detects possible read-errors on your backup targets (Note that a "btrfs scrub" is still more effective for that purpose).
See btrbk archive command in btrbk(1) for more details.
This example uses a USB disk as "stream-fifo" for transferring (cloning) of btrfs subvolumes:
-
For all source subvolumes (in order of generation):
btrfs send /source/subvolX -p PARENT > /usbdisk/streamN -
At the target location, restore the streams (in order of generation):
cat /usbdisk/streamN | btrfs receive /target
This approach has the advantage that you don't need to reformat your USB disk. This works fine, but be aware that you may run into trouble if a single stream gets corrupted, making all subsequent streams unusable.
If you use dd (e.g. in order to clone a partition), make sure you
don't mount the cloned filesystem at the same time as the original
one. You will end up having multiple filesystems sharing identical
UUID, which will break things. If you really want to do this, make
sure to run:
btrfstune -u /dev/sdaX
which changes the UUID of the given device. Note that the btrfs subvolumes still share identical UUID's, but at least the kernel can cope with it (see this post on stackexchange ).
Btrbk on the other hand relies on subvolume UUID's being universally unique, and uses them as hash keys for identifying and caching filesystem and subvolume trees, which leads to undefined behavior if multiple identical UUID's are processed.
You probably restored a backup with send-receive, and made it
read/write using btrfs property set. This is bad, as all snapshots
and backups will inherit this identical "Received UUID", which results
in all these subvolumes will be treated as "containing same data".
To fix this, create a "proper" snapshot:
# cd /mnt/btr_pool
# mv mysubvolume mysubvolume.broken
# btrfs subvolume snapshot mysubvolume.broken mysubvolume
Now, mysubvolume should have an empty "Received UUID". Note that in
order to have a clean environment, you also need to fix all subvolumes
(snapshots as well as backups) that you created with the broken
subvolume.
Check if there are more broken subvolumes:
# btrfs subvolume show mysubvolume.broken
# btrfs subvolume list -a -R /mnt/btr_pool | grep <"Received UUID" from above>
# btrfs subvolume list -a -R /mnt/btr_backup | grep <"Received UUID" from above>
Either delete them (they won't be used for incremental send-receive anyways), or clean them as follows:
# btrfs subvolume snapshot listed_ro_subvol listed_ro_subvol.rw
# btrfs subvolume delete listed_ro_subvol
# btrfs subvolume snapshot -r listed_ro_subvol.rw listed_ro_subvol
# btrfs subvolume delete listed_ro_subvol.rw
Finally, don't forget to delete the broken source subvolume:
# btrfs subvolume delete mysubvolume.broken
You should now have a clean environment, and btrbk will not complain any more.
If your file system was created with btrfs-progs < 4.16, the btrfs root subvolume (id=5) has no UUID. You can check this by calling:
# btrfs subvolume show /mnt/btr_pool
/
Name: <FS_TREE>
UUID: -
[...]
Without a UUID, the snapshots would get no parent_uuid, leaving btrbk unable to track parent/child relationships. In this case, btrbk refuses to create snapshots and backups.