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Description:

rotatebackups 8.1

Backups are good for you. Most people learn this the hard way (including me).
Nowadays my Linux laptop automatically creates a full system snapshot every
four hours by pushing changed files to an rsync daemon running on the server
in my home network and creating a snapshot afterwards using the cp -al
command (the article Easy Automated Snapshot-Style Backups with Linux and
Rsync explains the basic technique). The server has a second disk attached
which asynchronously copies from the main disk so that a single disk failure
doesn’t wipe all of my backups (the “time delayed replication” aspect has also
proven to be very useful).
Okay, cool, now I have backups of everything, up to date and going back in
time! But I’m running through disk space like crazy… A proper deduplicating
filesystem would be awesome but I’m running crappy consumer grade hardware and
e.g. ZFS has not been a good experience in the past. So I’m going to have to
delete backups…
Deleting backups is never nice, but an easy and proper rotation scheme can help
a lot. I wanted to keep things manageable so I wrote a Python script to do it
for me. Over the years I actually wrote several variants. Because I kept
copy/pasting these scripts around I decided to bring the main features together
in a properly documented Python package and upload it to the Python Package
Index.
The rotate-backups package is currently tested on cPython 2.7, 3.5+ and PyPy
(2.7). It’s tested on Linux and Mac OS X and may work on other unixes but
definitely won’t work on Windows right now.

Features
Installation
Usage

Command line
Configuration files
Customizing the rotation algorithm
Supported configuration options

How it works
Contact
License

Features

Dry run mode
Use it. I’m serious. If you don’t and rotate-backups eats more backups
than intended you have no right to complain ;-)

Flexible rotation
Rotation with any combination of hourly, daily, weekly, monthly and yearly
retention periods.

Fuzzy timestamp matching in filenames
The modification times of the files and/or directories are not relevant. If
you speak Python regular expressions, here is how the fuzzy matching
works:
# Required components.
(?P<year>\d{4}) \D?
(?P<month>\d{2}) \D?
(?P<day>\d{2}) \D?
(
# Optional components.
(?P<hour>\d{2}) \D?
(?P<minute>\d{2}) \D?
(?P<second>\d{2})?
)?

All actions are logged
Log messages are saved to the system log (e.g. /var/log/syslog) so you
can retrace what happened when something seems to have gone wrong.

Installation
The rotate-backups package is available on PyPI which means installation
should be as simple as:
$ pip install rotate-backups
There’s actually a multitude of ways to install Python packages (e.g. the per
user site-packages directory, virtual environments or just installing
system wide) and I have no intention of getting into that discussion here, so
if this intimidates you then read up on your options before returning to these
instructions ;-).

Usage
There are two ways to use the rotate-backups package: As the command line
program rotate-backups and as a Python API. For details about the Python
API please refer to the API documentation available on Read the Docs. The
command line interface is described below.

Command line
Usage: rotate-backups [OPTIONS] [DIRECTORY, ..]
Easy rotation of backups based on the Python package by the same name.
To use this program you specify a rotation scheme via (a combination of) the
--hourly, --daily, --weekly, --monthly and/or --yearly options and the
directory (or directories) containing backups to rotate as one or more
positional arguments.
You can rotate backups on a remote system over SSH by prefixing a DIRECTORY
with an SSH alias and separating the two with a colon (similar to how rsync
accepts remote locations).
Instead of specifying directories and a rotation scheme on the command line you
can also add them to a configuration file. For more details refer to the online
documentation (see also the --config option).
Please use the --dry-run option to test the effect of the specified rotation
scheme before letting this program loose on your precious backups! If you don’t
test the results using the dry run mode and this program eats more backups than
intended you have no right to complain ;-).
Supported options:

Option
Description

-M, --minutely=COUNT
In a literal sense this option sets the number of “backups per minute” to
preserve during rotation. For most use cases that doesn’t make a lot of
sense :-) but you can combine the --minutely and --relaxed options to
preserve more than one backup per hour. Refer to the usage of the -H,
--hourly option for details about COUNT.

-H, --hourly=COUNT
Set the number of hourly backups to preserve during rotation:

If COUNT is a number it gives the number of hourly backups to preserve,
starting from the most recent hourly backup and counting back in time.
Alternatively you can provide an expression that will be evaluated to get
a number (e.g. if COUNT is “7 * 2” the result would be 14).
You can also pass “always” for COUNT, in this case all hourly backups are
preserved.
By default no hourly backups are preserved.

-d, --daily=COUNT
Set the number of daily backups to preserve during rotation. Refer to the
usage of the -H, --hourly option for details about COUNT.

-w, --weekly=COUNT
Set the number of weekly backups to preserve during rotation. Refer to the
usage of the -H, --hourly option for details about COUNT.

-m, --monthly=COUNT
Set the number of monthly backups to preserve during rotation. Refer to the
usage of the -H, --hourly option for details about COUNT.

-y, --yearly=COUNT
Set the number of yearly backups to preserve during rotation. Refer to the
usage of the -H, --hourly option for details about COUNT.

-t, --timestamp-pattern=PATTERN
Customize the regular expression pattern that is used to match and extract
timestamps from filenames. PATTERN is expected to be a Python compatible
regular expression that must define the named capture groups ‘year’,
‘month’ and ‘day’ and may define ‘hour’, ‘minute’ and ‘second’.

-I, --include=PATTERN
Only process backups that match the shell pattern given by PATTERN. This
argument can be repeated. Make sure to quote PATTERN so the shell doesn’t
expand the pattern before it’s received by rotate-backups.

-x, --exclude=PATTERN
Don’t process backups that match the shell pattern given by PATTERN. This
argument can be repeated. Make sure to quote PATTERN so the shell doesn’t
expand the pattern before it’s received by rotate-backups.

-j, --parallel
Remove backups in parallel, one backup per mount point at a time. The idea
behind this approach is that parallel rotation is most useful when the
files to be removed are on different disks and so multiple devices can be
utilized at the same time.
Because mount points are per system the -j, --parallel option will also
parallelize over backups located on multiple remote systems.

-p, --prefer-recent
By default the first (oldest) backup in each time slot is preserved. If
you’d prefer to keep the most recent backup in each time slot instead then
this option is for you.

-r, --relaxed
By default the time window for each rotation scheme is enforced (this is
referred to as strict rotation) but the -r, --relaxed option can be used
to alter this behavior. The easiest way to explain the difference between
strict and relaxed rotation is using an example:

When using strict rotation and the number of hourly backups to preserve
is three, only backups created in the relevant time window (the hour of
the most recent backup and the two hours leading up to that) will match
the hourly frequency.
When using relaxed rotation the three most recent backups will all match
the hourly frequency (and thus be preserved), regardless of the
calculated time window.

If the explanation above is not clear enough, here’s a simple way to decide
whether you want to customize this behavior or not:

If your backups are created at regular intervals and you never miss an
interval then strict rotation (the default) is probably the best choice.
If your backups are created at irregular intervals then you may want to
use the -r, --relaxed option in order to preserve more backups.

-i, --ionice=CLASS
Use the “ionice” program to set the I/O scheduling class and priority of
the “rm” invocations used to remove backups. CLASS is expected to be one of
the values “idle” (3), “best-effort” (2) or “realtime” (1). Refer to the
man page of the “ionice” program for details about these values. The
numeric values are required by the ‘busybox’ implementation of ‘ionice’.

-c, --config=FILENAME
Load configuration from FILENAME. If this option isn’t given the following
default locations are searched for configuration files:

/etc/rotate-backups.ini and /etc/rotate-backups.d/*.ini
~/.rotate-backups.ini and ~/.rotate-backups.d/*.ini
~/.config/rotate-backups.ini and ~/.config/rotate-backups.d/*.ini

Any available configuration files are loaded in the order given above, so
that sections in user-specific configuration files override sections by the
same name in system-wide configuration files. For more details refer to the
online documentation.

-C, --removal-command=CMD
Change the command used to remove backups. The value of CMD defaults to
rm ``-f``R. This choice was made because it works regardless of whether
“backups to be rotated” are files or directories or a mixture of both.
As an example of why you might want to change this, CephFS snapshots are
represented as regular directory trees that can be deleted at once with a
single ‘rmdir’ command (even though according to POSIX semantics this
command should refuse to remove nonempty directories, but I digress).

-u, --use-sudo
Enable the use of “sudo” to rotate backups in directories that are not
readable and/or writable for the current user (or the user logged in to a
remote system over SSH).

-S, --syslog=CHOICE
Explicitly enable or disable system logging instead of letting the program
figure out what to do. The values ‘1’, ‘yes’, ‘true’ and ‘on’ enable system
logging whereas the values ‘0’, ‘no’, ‘false’ and ‘off’ disable it.

-f, --force
If a sanity check fails an error is reported and the program aborts. You
can use --force to continue with backup rotation instead. Sanity checks
are done to ensure that the given DIRECTORY exists, is readable and is
writable. If the --removal-command option is given then the last sanity
check (that the given location is writable) is skipped (because custom
removal commands imply custom semantics).

-n, --dry-run
Don’t make any changes, just print what would be done. This makes it easy
to evaluate the impact of a rotation scheme without losing any backups.

-v, --verbose
Increase logging verbosity (can be repeated).

-q, --quiet
Decrease logging verbosity (can be repeated).

-h, --help
Show this message and exit.

Configuration files
Instead of specifying directories and rotation schemes on the command line you
can also add them to a configuration file.
Configuration files are text files in the subset of ini syntax supported by
Python’s configparser module. They can be located in the following places:

Directory
Main configuration file
Modular configuration files

/etc
/etc/rotate-backups.ini
/etc/rotate-backups.d/*.ini

~
~/.rotate-backups.ini
~/.rotate-backups.d/*.ini

~/.config
~/.config/rotate-backups.ini
~/.config/rotate-backups.d/*.ini

The available configuration files are loaded in the order given above, so that
user specific configuration files override system wide configuration files.
You can load a configuration file in a nonstandard location using the command
line option --config, in this case the default locations mentioned above
are ignored.
Each section in the configuration defines a directory that contains backups to
be rotated. The options in each section define the rotation scheme and other
options. Here’s an example based on how I use rotate-backups to rotate the
backups of the Linux installations that I make regular backups of:
# /etc/rotate-backups.ini:
# Configuration file for the rotate-backups program that specifies
# directories containing backups to be rotated according to specific
# rotation schemes.

[/backups/laptop]
hourly = 24
daily = 7
weekly = 4
monthly = 12
yearly = always
ionice = idle

[/backups/server]
daily = 7 * 2
weekly = 4 * 2
monthly = 12 * 4
yearly = always
ionice = idle

[/backups/mopidy]
daily = 7
weekly = 4
monthly = 2
ionice = idle

[/backups/xbmc]
daily = 7
weekly = 4
monthly = 2
ionice = idle
As you can see in the retention periods of the directory /backups/server in
the example above you are allowed to use expressions that evaluate to a number
(instead of having to write out the literal number).
Here’s an example of a configuration for two remote directories:
# SSH as a regular user and use `sudo' to elevate privileges.
[server:/backups/laptop]
use-sudo = yes
hourly = 24
daily = 7
weekly = 4
monthly = 12
yearly = always
ionice = idle

# SSH as the root user (avoids sudo passwords).
[server:/backups/server]
ssh-user = root
hourly = 24
daily = 7
weekly = 4
monthly = 12
yearly = always
ionice = idle
As this example shows you have the option to connect as the root user or to
connect as a regular user and use sudo to elevate privileges.

Customizing the rotation algorithm
Since publishing rotate-backups I’ve found that the default rotation
algorithm is not to everyone’s satisfaction and because the suggested
alternatives were just as valid as the choices that I initially made,
options were added to expose the alternative behaviors:

Default
Alternative

Strict rotation (the time window
for each rotation frequency is
enforced).
Relaxed rotation (time windows are
not enforced). Enabled by the
-r, --relaxed option.

The oldest backup in each time slot
is preserved and newer backups in
the time slot are removed.
The newest backup in each time slot
is preserved and older backups in
the time slot are removed. Enabled
by the -p, --prefer-recent
option.

Supported configuration options

Rotation schemes are defined using the minutely, hourly, daily,
weekly, monthly and yearly options, these options support the
same values as documented for the command line interface.
The timestamp-pattern option can be used to customize the regular
expression that’s used to extract timestamps from filenames. The value is
expected to be a Python compatible regular expression that must contain the
named capture groups ‘year’, ‘month’ and ‘day’ and may contain the groups
‘hour’, ‘minute’ and ‘second’. As an example here is the default regular
expression:
# Required components.
(?P<year>\d{4} ) \D?
(?P<month>\d{2}) \D?
(?P<day>\d{2} ) \D?
(?:
# Optional components.
(?P<hour>\d{2} ) \D?
(?P<minute>\d{2}) \D?
(?P<second>\d{2})?
)?
Note how this pattern spans multiple lines: Regular expressions are compiled
using the re.VERBOSE flag which means whitespace (including newlines) is
ignored.

The include-list and exclude-list options define a comma separated
list of filename patterns to include or exclude, respectively:

Make sure not to quote the patterns in the configuration file,
just provide them literally.
If an include or exclude list is defined in the configuration file it
overrides the include or exclude list given on the command line.

The prefer-recent, strict and use-sudo options expect a boolean
value (yes, no, true, false, 1 or 0).
The removal-command option can be used to customize the command that is
used to remove backups.
The ionice option expects one of the I/O scheduling class names idle,
best-effort or realtime (or the corresponding numbers).
The ssh-user option can be used to override the name of the remote SSH
account that’s used to connect to a remote system.

How it works
The basic premise of rotate-backups is fairly simple:

You point rotate-backups at a directory containing timestamped backups.
It will scan the directory for entries (it doesn’t matter whether they are
files or directories) with a recognizable timestamp in the name.

Note
All of the matched directory entries are considered to be backups
of the same data source, i.e. there’s no filename similarity logic
to distinguish unrelated backups that are located in the same
directory. If this presents a problem consider using the
--include and/or --exclude options.

The user defined rotation scheme is applied to the entries. If this doesn’t
do what you’d expect it to you can try the --relaxed and/or
--prefer-recent options.
The entries to rotate are removed (or printed in dry run).

Contact
The latest version of rotate-backups is available on PyPI and GitHub. The
documentation is hosted on Read the Docs and includes a changelog. For bug
reports please create an issue on GitHub. If you have questions, suggestions,
etc. feel free to send me an e-mail at peter@peterodding.com.

License
This software is licensed under the MIT license.
© 2020 Peter Odding.