rotate-backups: Simple command line interface for backup rotation

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 2.6, 2.7, 3.4, 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
• 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.
-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", "best-effort" or "realtime". Refer to the man page of the "ionice" program for details about these values.
-c, --config=PATH	Load configuration from the pathname given by PATH. If this option isn't given two default locations are checked: "~/.rotate-backups.ini" and "/etc/rotate-backups.ini". The first of these two configuration files to exist is loaded. For more details refer to the online documentation.
-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).
-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	Make more noise (increase logging verbosity). Can be repeated.
-q, --quiet	Make less noise (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.

By default two locations are checked for a configuration file, these are ~/.rotate-backups.ini and /etc/rotate-backups.ini. The first of these that exists is loaded. You can load a configuration file in a nonstandard location using the command line option --config.

Configuration files use the familiar INI syntax. Each section 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.

Contact

The latest version of rotate-backups is available on PyPI and GitHub. The documentation is hosted on Read the Docs. 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.

© 2016 Peter Odding.