`volume <volume-directory|<ulr>`: Usually the mount point of a btrfs filesystem mounted with `subvolid=5`.
`subvolume <subvolume-name|<url>`: Subvolume to be backed up, relative to `<volume-directory>`.
`snapshot_dir <directory>`: Directory in which the btrfs snapshots are created, relative to `<volume-directory>`. Hast to be created **manually**!
`target <target-directory>|<url>`: Target directory where the backup subvolumes are to be created. Multiple target sections are allowed.
`url`: Accepted formats are:
*`ssh://<hostname>[:<port>]/<directory>`
*`<hostname>:<directory>`
`hostname`: Either a host name, IPv4 or IPv6 address
`timestamp_format short|long|long-iso`: This becomes relevant for setups with multiple btrbk instances, e.g. many snapshot-only instances (spread around the world), and a fetch-only instance on the backup server. Make sure to run btrbk with the same time zone on every host, e.g. by setting the TZ environment variable (see tzset(3)).
### Retention
`snapshot_preserve <retention_policy>`
`snapshot_preserve_min all|latest|<number>{h,d,w,m,y}`: Preserve all snapshots for a minimum amount of hours (h), days (d), weeks (w), months (m) or years (y).
`target_preserve <retention_policy>`
`target_preserve_min all|latest|no|<number>{h,d,w,m,y}`: Preserve all snapshots for a minimum amount of hours (h), days (d), weeks (w), months (m) or years (y). If set to "no", only the backups following the `target_preserve` policy are created.
`<retention_policy>`: `[<hourly>h] [<daily>d] [<weekly>w] [<monthly>m] [<yearly>y]`. Defines how many backups of each period should be preserved.
### SSH and Data Stream Options
`ssh_compression yes|no`
`stream_compress <compress_command>`: Compress the btrfs send stream before transferring it from/to remote locations.
`stream_buffer <size>|no`: This can give a speed improvement (measured up to 20%) on both local or remote operations, but also increases system load. Make sure that the `mbuffer` command is available. Leave this option disabled if your main concern is a stable backup process: while recent versions of mbuffer have proven reliable, it is often desirable to keep things simple rather than adding an additional, multi-threaded process to the command pipe.
`rate_limit <rate>|no`: Limit the read rate of the btrfs send stream to `<rate>` bytes per second. Implies the `stream_buffer` option.
### System Options
`transaction_syslog <facility>|no`: Log all transactions to syslog.
`lockfile <file>|no`
## Example: Local Snapshots and Backup
```
timestamp_format long
snapshot_preserve_min 2d
snapshot_preserve 24h 7d 4w 6m
target_preserve_min no
target_preserve 7d 4w 6m
volume /mnt/12tb1-top-level
snapshot_dir @snap
target /mnt/12tb2-top-level/@snap
subvolume @home
subvolume @
```
Mount top-level subvolume:
```shell
mount -o subvolid=5 /dev/mapper/some-disk /mnt/12tb1-top-level
```
Manually create snapshot directory:
```shell
btrfs subvolume create /mnt/12tb1-top-level/@snap
btrfs subvolume create /mnt/12tb2-top-level/@snap
```
Snapshots only:
```shell
btrbk snapshot
```
Backup only:
```shell
btrbk resume
```
Create an additional snapshot of @home:
```shell
btrbk snapshot @home
```
## Testing on Local Host
```shell
sudo mkdir -p /mnt/top-level
ls /mnt/top-level/@ || sudo mount -o subvolid=5 /dev/mapper/luks-ea7099e3-320d-4eb3-a4c3-9910a9af817b /mnt/top-level
ls /mnt/top-level/@snap || sudo btrfs subvolume create /mnt/top-level/@snap
ls /mnt/top-level/@foo || {
sudo btrfs subvolume create /mnt/top-level/@foo
sudo touch /mnt/top-level/@foo/bar
}
```
```shell
ls ~/btrbk-usb.img || {
fallocate -l 1G ~/btrbk-usb.img
sudo mkfs.btrfs ~/btrbk-usb.img
# Mount and create subvolume @
}
sudo mkdir -p /mnt/usb-top-level
ls /mnt/usb-top-level/@ || sudo mount -o subvolid=5 ~/btrbk-usb.img /mnt/usb-top-level
ls /mnt/usb-top-level/@snap || sudo btrfs subvolume create /mnt/usb-top-level/@snap
}
```
```shell
cat > ~/btrbk.cfg <<'EOF'
timestamp_format long
snapshot_preserve_min 2d
snapshot_preserve 24h 7d 4w 6m
target_preserve_min no
target_preserve 7d 4w 6m
volume /mnt/top-level
snapshot_dir @snap
target /mnt/usb-top-level/@snap
subvolume @foo
EOF
```
```shell
# Check configuration.
sudo btrbk -c ~/btrbk.cfg config print
sudo btrbk -c ~/btrbk.cfg config list
# Dry run.
sudo btrbk -c ~/btrbk.cfg run -n
# Create first snapshot.
sudo btrbk -c ~/btrbk.cfg run
# Print schedule.
sudo btrbk -c ~/btrbk.cfg run -n -S
sleep 5m
sudo btrbk -c ~/btrbk.cfg run
# List snapshots
sudo btrbk -c ~/btrbk.cfg list
```
### NixOS Config
```nix
{ config, pkgs, ... }:
{
services.btrbk = {
extraPackages = [ pkgs.lz4 ];
# Lowest scheduling priority.
niceness = 19;
# Set of btrbk instances. The instance named btrbk is the default one.
instances = {
# This is the configuration equivalent to
# README.md section "Testing on Local Host".
"testing-on-local-host" = {
# The timer is disabled. The service has to be invoked manually.
onCalendar = null;
#onCalendar = "hourly";
#onCalendar = "*:0/15"; # Every 15min
# Configuration options for btrbk. Nested attrsets translate to subsections.
settings = {
timestamp_format = "long";
stream_compress = "lz4";
snapshot_preserve_min = "2d";
snapshot_preserve = "24h 7d 4w 6m";
target_preserve_min = "no";
target_preserve = "7d 4w 6m";
volume."/mnt/top-level" = {
snapshot_dir = "@snap";
target = "/mnt/usb-top-level/@snap";
subvolume = "@foo";
};
};
};
};
};
}
```
## pi3bplus Host Config
A local `btrbk` instance manages snapshots and local backups.
Another remote backup server periodically pulls snapshots to create remote backups. Here is its config:
