dsnapshot 0.0.3

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.

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, seoncds 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 a script 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", "echo second script"]
post_exec = ["echo $DSNAPSHOT_SRC $DSNAPSHOT_DST", "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.

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

The default arguments for rsync can be changed.

[snapshot.example.rsync]
rsync_args = ["-ahv", "--numeric-ids", "--modify-window", "1"]

If the default rsync from the 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 use 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:

[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 = []

Example 1: 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 = 7
span.2.interval = "1 days"
span.3.nr = 4
span.3.interval = "7 days"
span.4.nr = 12
span.4.interval = "30 days"
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"

Exasmple 2: Backup to a remote host

[snapshot.example]
span.1.nr = 6
span.1.interval = "4 hours"
[snapshot.example.rsync]
src = "~/example"
dst = "~/backup/example"
dst_addr = "other_host"

Example 3: Backup from a remote host

[snapshot.example]
span.1.nr = 6
span.1.interval = "4 hours"
[snapshot.example.rsync]
src = "~/example"
src_addr = "other_host"
dst = "~/backup/example"

Example 4: 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"

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.

diskusage

Calculates the actual disk usage of the specified snapshot.

restore

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

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.

* */4 * * * dsnapshot backup -c my_config.toml

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

Credit

The creator of rsnapshot which inspired me to create dsnapshot.