dsnapshot 0.1.4

dsnapshot

dsnapshot is a filesystem snapshot utility based on rsync.

dsnapshot makes it easy to keep periodic snapshots of local and remote machines over ssh.

dsnapshot uses hard links to create an illusion of multiple full backups while in the background only occupying the space needed for one full plus the differences. This greatly reduces the disk space required.

Onces dsnapshot is set up your backups can happen automatically, usually trigged via e.g. a cron job. Because dsnapshot only keeps a fixed number of snapshots, as configured, the amount of disk space used will not continue to grow.

The destination, where the snapshots are stored, can be optionally encrypted. This is useful when the snapshots are stored in the cloud.

Getting Started

dsnapshot depends on the following software packages:

• D compiler (dmd 2.079+, ldc 1.11.0+)

It is recommended to install the D compiler by downloading it from the official distribution page.

curl -fsS https://dlang.org/install.sh | bash -s dmd

Once the d compiler is installed you can compile and run dsnapshot.

git clone https://github.com/joakim-brannstrom/dsnapshot.git
cd dsnapshot
dub build -b release
./build/dsnapshot -h

Done! Have fun. Don't be shy to report any issue that you find.

Configuration

dsnapshot look by default for the configuration file .dsnapshot.toml in the current directory. The configuration file can be manually specified via -c.

The configuration structure is named snapshots with their individual configuration.

Each snapshot consist of at least one span and src/dst configuration in the rsync section.

[snapshot.example]
span.1.nr = 6
span.1.interval = "4 hours"
[snapshot.example.rsync]
src = "path/to/src"
dst = "path/to/where/to/backup/src"

Note that if the paths are relative they will be relative to where dsnapshot is executed for a local address.

If the source or destination isn't on the local computer then an address can be specified in the rsync section:

src_addr = "foo.com"
# or
dst_addr = "foo.com"

Spans

dsnapshot is aware of how often you want to take snapshots. The span configuration is what controls how many and with what intervals snapshots are created and kept on disk.

A basic span is a unique identifier (numerical value), number of snapshots and the interval.

span.<id>.nr = <numerical value>
span.<id>.interval = "<value> <unit>"

The supported unites for the interval are weeks, days, hours, minutes, seconds and msecs. These can be written in any order, combination and multiple times.

Multiple spans are concatenated together to a snapshot layout. The snapshots that are taken are automatically mapped into the specified layout as time progress. Lets say the following configuration:

span.1.nr = 2
span.1.interval = "12 hours"
span.2.nr = 7
span.2.interval = "7 days"

It will result in 9 backups as such:

date:    now                                 now-8 days
layout:  __1__2____3____4____5____6____7____8____9
span nr: --1--|--------------2-------------------|

There may intermittently exist +1 backup because dsnapshot scans the destination for backups before it creates its new one.

The default span is:

span.1.nr = 6
span.1.interval = "4 hours"
span.2.nr = 6
span.2.interval = "1 days"
span.2.nr = 3
span.2.interval = "1 weeks"

It keeps the backups for up to a month with less and less frequency.

Advanced config

dsnapshot can run scripts (hooks) before and after a snapshot is created. The snapshot process will stop if any of the scripts fail.

[snapshot.example]
pre_exec = ["echo $DSNAPSHOT_SRC $DSNAPSHOT_DST $DSNAPSHOT_DATA_DST $DSNAPSHOT_LATEST $DSNAPSHOT_DATA_LATEST", "echo second script"]
post_exec = ["echo $DSNAPSHOT_SRC $DSNAPSHOT_DST $DSNAPSHOT_DATA_DST $DSNAPSHOT_LATEST $DSNAPSHOT_DATA_LATEST", "echo second script"]

Normally the CPU and IO is set to low priority for the rsync process. This can be turned off with:

[snapshot.example.rsync]
low_prio = false

The use of --link-dest for rsync can be turned off:

[snapshot.example.rsync]
link_dest = false

Normally dsnapshot is prohibited from crossing the filesystem. This can be turned off.

[snapshot.example.rsync]
cross_fs = false

Dsnapshot can be configured to exclude directories. The path is relative to src. See man rsync for more details.

[snapshot.example.rsync]
exclude = ["path/to/exclude"]
# which is the actual path: src/path/to/exclude

The default arguments for rsync can be changed.

[snapshot.example.rsync]
rsync_backup_args = ["-ahv", "--numeric-ids", "--modify-window", "1", "--delete", "--delete-excluded", "--partial"]
rsync_restore_args = ["-ahv", "--numeric-ids", "--modify-window", "1"]

Lets say that rsync from $PATH can't be used. In that case dsnapshot can be configured to use an alternative rsync.

[snapshot.example.rsync]
rsync_cmd = "path/to/rsync"

The command used to calculate the disk usage is by default du but can be changed.

[snapshot.example.rsync]
diskusage_cmd = ["path/to/du", "-hcs"]

The command used for remote shell execution of snapshots can be configured. It has overlap with rsync_rsh. The difference is that rsh is used as is while rsync_rsh configures rsync via --rsh=<rsync_rsh>.

[snapshot.example]
rsh = ["ssh", "-p1234"]
[snapshot.example.rsync]
rsync_rsh = "ssh -p1234"

The location of where to find dsnapshot on the remote host can be configured. This is needed when doing a local to remote snapshot:

[snapshot.example]
dsnapshot = "/path/to/dsnapshot"

A progress bar, via rsync, is displayed when dsnapshot is executed in interactive mode. This can be changed or turned off.

[snapshot.example.rsync]
progress = ["--info=progress1"]
# or turn off
progress = []

The user and group for files can be saved via the excellent fakeroot program. This make it possible to both e.g. backup files owned by root on one host to another where one do not have root access. By not needing root on the remote server the security is improved and simplified.

[snapshot.example.rsync]
fakeroot = true
# additionally the arguments for fakeroot can be changed
fakeroot_args = ["fakeroot", "-u", "-s" "$$SAVE_ENV_FILE$$", "-i", "$$SAVE_ENV_FILE$$"]
# or change to using fakeroot-ng
fakeroot_args = ["fakeroot-ng", "-d", "-p", "$$SAVE_ENV_FILE$$"]
# the rsync command that is executed is the one from rsync_cmd
# this is only used when backing up to another host
rsync_fakeroot_args = ["--rsync-path"]

Configuring encfs for encrypted snapshots

encfs can be used to encrypt the snapshots. The configurations parameters for encfs is in the encfs group.

The encfs encrypted data (in encfs terms the rootDir). This must be located outside of the destination. Both dst and encrypted_path must exist before running dsnapshot.

[snapshot.example.encfs]
encrypted_path = "/foo/bar/encfs"
[snapshot.example.rsync]
dst = "/foo/bar/dst"

If the configuration file for the encrypted data is not located in the root of encrypted_path it can be specified.

[snapshot.example.encfs]
config = "path/to/config.xml"

The password for opening the encrypted data can be specified in two ways. The first one uses echo to send the password to encfs when it asks for the password. To avoid printing the password in the logs that dsnapshot produces it is put in the environment variable DSNAPSHOT_ENCFS_PWD. This may be insecure for your use case so think about it.

[snapshot.example.encfs]
passwd = "foo"

The other way of specifying the password is to replace the arguments that dsnapshot uses with yours.

[snapshot.example.encfs]
# to use an external password program you could instead do this
mount_cmd = ["encfs", "-i", "1", "--extpass", "ssh-askpass"]

To change what parameters are used when mounting and unmounting. This is useful when e.g. debugging by add -v.

[snapshot.example.encfs]
mount_cmd = ["encfs", "-i", "1"]
unmount_cmd = ["encfs", "-u"]

To pass on extra arguments to FUSE when mounting and unmounting.

[snapshot.example.encfs]
mount_fuse_opts = ["-o", "myopt"]
unmount_fuse_opts = ["-o", "myopt"]

Example 1: Simple backup on localhost

This is a simple configuration that keeps backups for up to a month.

[snapshot.example]
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"

To automate the backups you can put this line in crontab:

0 */4 * * * dsnapshot backup -c my_config.toml --margin "10 minutes"

Exasmple 2: Backup to a remote host

This puts the backups on the host specified in dst_addr. The directory in dst will be relative to the home directory on other_host.

[snapshot.example]
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"
dst_addr = "other_host"

Example 3: Backup from a remote host

This backups other_host to the computer where dsnapshot is executed.

[snapshot.example]
[snapshot.example.rsync]
src = "~/example"
src_addr = "other_host"
dst = "~/backup/example"

Example 4: Backups kept over a year

This will create create a total span of backups that has a higher frequency the first day (4 hours interval) that will turn into one backup per day for a week. This is then followed lowered to one per month after that period.

[snapshot.example]
span.1.nr = 6
span.1.interval = "4 hours"
span.2.nr = 6
span.2.interval = "1 days"
span.3.nr = 3
span.3.interval = "1 weeks"
span.4.nr = 11
span.4.interval = "30 days"
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"

Example 5: Backup a sql dump

In this example dsnapshot will backup the raw dump of a postgresql database by executing a script that dumps the database to a file via the pre_exec hook.

[snapshot.example]
span.1.nr = 7
span.1.interval = "1 days"
pre_exec = ["mkdir -p $DSNAPSHOT_SRC", "pg_dumpall -Upostgres > \"$DSNAPSHOT_SRC/dump.sql\""]
post_exec = ["rm \"$DSNAPSHOT_SRC/dump.sql\""]
[snapshot.example.rsync]
src = "~/my_script_dump"
dst = "~/backup/my_script_dump"

Example 6: Backup / to a remote host

In this example dsnapshot will backup the most relevant files from / in order to ease a restore of the server. To improve the security dsnapshot uses fakeroot to avoid the need for being root on the remote server when backing up files owned by root.

The example expects the user example_backup to exist on the remote server and have a ssh key registered that is used by the local root when transferring and running commands on dst_addr.

The example uses the default layout which mean the backups are kept for one month.

[snapshot.luggage_root]
dsnapshot = "/home/example_backup/dsnapshot"
rsh = ["ssh", "-l", "example_backup"]
[snapshot.luggage_root.rsync]
exclude = ["dev/", "home/", "media/", "mnt/", "opt/", "proc/", "run/", "sys/",
"tmp/", "var/", "sbin/", "lost+found/", "usr/", "bin/", "lib/", "lib64/",
"snap/", "lib32/", "libx32/"]
src = "/"
dst = "/home/example_backup/root"
dst_addr = "example_backup@lipwig"
fakeroot = true

Example 7: Encrypt the snapshots

In this example the directories used in encrypted_path, src and dst exists before dsnapshot is executed. encfs has been executed with the arguments

encfs -f -v ~/backup/example_encfs ~/backup/example

to let it create a configuration in ~/backup/example_encfs.

dsnasphot will then open encrypted_path at dst with encfs before doing anything.

The end result is that the snapshots that are taken will be encrypted. This is useful for storing the snapshots on an untrusted cloud provider.

[snapshot.example]
[snapshot.example.encfs]
passwd = "my pwd"
# this is where you store it in e.g. your cloud provider
encrypted_path = "~/backup/example_encfs"
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"

Example 8: Run dedupe on a btrfs filesystem

BTRFS supports deduplication of blocks on the filesystem. In this example one of the many tools to tell the kernel which blocks should be deduplicated are called as a post processing step. This can be quite expensive to do so may not be optimal to always add it as a post_exec hook.

If the snapshots are stored locally:

[snapshot.example]
post_exec = ["cp $DSNAPSHOT_LATEST/duperemove.sqlite3 DSNAPSHOT_DST || true",
    "duperemove -dhr --hashfile ${DSNAPSHOT_DST}/duperemove.sqlite3 $DSNAPSHOT_DATA_LATEST ${DSNAPSHOT_DATA_DST}"]
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"

If the snapshots are stored on a remote host:

[snapshot.example]
post_exec = ["echo cp $DSNAPSHOT_LATEST/duperemove.sqlite3 ${DSNAPSHOT_DST#*:} | ssh remote || true",
    "echo duperemove -dhr --hashfile ${DSNAPSHOT_DST#*:}/duperemove.sqlite3 $DSNAPSHOT_DATA_LATEST ${DSNAPSHOT_DATA_DST#*:} | ssh remote"]
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"
dst_addr = "remote"

Usage

dsnapshot is divided into command groups like git.

backup

Executes all snapshots in the configuration file.

verifyconfig

This verify the configuration for errors without executing any commands. Run with -v trace for the most verbose output.

admin

Administrator commands such as calculating the disk usage.

restore

Restores the snapshot that closest matches the specified date or if none is given the latest.

watch

dsnapshot watches src for changes. When a change is detected it will queue a snapshot to be taken as soon as the configured span allows it. This is useful if you want to take a snapshot as soon as the filesystem changes and only if it changes.

Automation

When you have a configuration file that you are happy with you may want to automate the execution of the backup command.

One way of automating is to use the tried and true crontab. Lets say you have configured dsnapshots first span to a 4 hours interval and the second is 1 day.

0 */4 * * * dsnapshot backup -c my_config.toml --margin "10 minutes"

Done! The snapshots will automatically spill over from the 4 hours span to the 1 day span over time.

systemd

Now that you have your config file set up, it's time to set up dsnapshot to be run automatically.

Since version 197 systemd supports timers, making cron unnecessary on a systemd system. Since version 212 persistent services are supported, replacing even anacron. Persistent timers are run at the next opportunity if the system was powered down when the timer was scheduled.

System Service

This is how to setup dsnapshot as a system service to create backups.

First create a service file: /etc/systemd/system/dsnapshot@.service

[Unit]
Description=dsnapshot backup (%I)

[Service]
Type=oneshot
Nice=19
IOSchedulingClass=idle
ExecStart=/path/to/dsnapshot backup -c /etc/dsnapshot/%I.toml --margin "10 minutes"

Then create a copy of this file for each configuration file you want to execute in /etc/dsnapshot. Change the name between the @ and the file type to the name of the configuration file. In this example it is assumed to be all. Modify OnCalendar to match how often you want your configuration to execute.

The template is expected to be placed in: /etc/systemd/system/dsnapshot-all.timer

[Unit]
Description=dsnapshot backup
RefuseManualStart=no
RefuseManualStop=no

[Timer]
Persistent=true
OnCalendar=*-*-* 0/4:00:00
Unit=dsnapshot@all.service

[Install]
WantedBy=timers.target

Then finally, enable and start:

systemctl enable --now dsnapshot-hourly.timer
# to manually trigger it
systemctl status -n999999 dsnapshot@all.service
# show the status
systemctl list-timers --user --all
systemctl status dsnapshot-all.timer
systemctl status dsnapshot@all.service
journalctl -l -u dsnapshot@all.service

Local User

The following is an example on how to make a simple timer that runs in the context of a user. It will even run if the user is not logged in. Every timed service needs a timer and a service file that is activated by the timer as follows.

Example of a service triggering backup

FILE ~/.local/share/systemd/user/dsnapshot@.service

[Unit]
Description=dsnapshot backup (%I)

[Service]
Type=oneshot
Nice=19
IOSchedulingClass=idle
ExecStart=/path/to/dsnapshot backup -c %h/.%I.toml --margin "10 minutes"

Example of a timer running every fourth hour every day

FILE ~/.local/share/systemd/user/dsnapshot-all.timer

[Unit]
Description=dsnapshot backup
RefuseManualStart=no
RefuseManualStop=no

[Timer]
Persistent=true
OnCalendar=*-*-* 0/4:00:00
Unit=dsnapshot@dsnapshot.service

[Install]
WantedBy=timers.target

And then to start it:

systemctl --user enable --now dsnapshot-all.timer
# to manually trigger it
systemctl --user status -n999999 dsnapshot@dsnapshot.service
# show the status
systemctl --user list-unit-files
systemctl --user list-timers --user --all
systemctl --user list-units -t service --all
systemctl --user status dsnapshot-all.timer
systemctl --user status dsnapshot@dsnapshot.service
journalctl -l -u dsnapshot@dsnapshot.service

For a complete explanation of the unit file see

man 5 systemd.unit

Credit

The creator of rsnapshot which inspired me to create dsnapshot.