Pukcab 1.5

2016-10-17

Introduction

pukcab is a lightweight, single-binary backup system for UNIX / Linux systems that stores de-duplicated, compressed and incremental backups on a remote server using just an SSH connection.

De-duplication happens not only between incremental backups of the same system but also between different systems. For example, it allows you to perform full backups of systems running the same OS with only minimal disk space for each additional system1.

Intended use

pukcab doesn’t compare to professional-grade backup systems, don’t expect it to be able to backup thousands of systems or dozens of terabytes of data.

It is, however, perfectly suitable for home users, hobbyists, UNIX / Linux enthusiasts or small tech-savy shops who want a flexible, yet dead-easy to setup and operate backup system with no bigger expenses than just a Linux box with a few terabytes of storage.

Little to no configuration should ever be required to satisfy most needs:

Features

Requirements

pukcab was written with UNIX-like operating systems in mind, it is therefore currently unsupported on Microsoft Windows2.

pukcab has been tested on the following operating systems and platforms3:

Backup server

To run a pukcab backup server, you will need:

The “scalable filesystem” requirement might seem surprising but, to store backups, you will need a modern filesystem that can gracefully handle thousands and thousands of files per directory, sometimes big, sometimes small.

On Linux, XFS, ext4 and Btrfs are known to work. FAT, NTFS or HFS cannot and must not be used.

Clients

The requirements for a client are very limited. In short, nearly any Linux/OS X box will do.

Installation

Just copy the pukcab binary5 into your path (/usr/bin/pukcab will be just fine) on the backup server and each client.

OS Platform Width Packages
Linux x86-64 64-bit ZIP
Linux i686 32-bit ZIP
Linux ARM 32-bit ZIP
Mac OS X x86-64 64-bit ZIP
any any any Source6

For RPM-based Linux distributions, YUM repositories are available:

Copy the .repo file into /etc/yum.repos.d and do either:

On the backup server

  1. create a dedicated user, if necessary (usually called pukcab) – this user does not need specific privileges (i.e. do NOT use root)
  2. allow key-based SSH login for that user
  3. optional: allow password-based SSH login and set a password for the dedicated user (if you want to be able to register new clients using that password)

On the clients (manual)

  1. create SSH keys for the user which will launch the backup (most probably root)
  2. add the user’s public key to the dedicated user’s authorized_keys on the backup server

On the clients (password registration)

  1. create SSH keys for the user which will launch the backup (most probably root)
  2. register to the backup server

Configuration

pukcab is configured with a simple INI-like text file:

; comment
name1 = number
name2 = "text value"
name3 = [ "list", "of", "text", "values" ]
[section1]
name4 = "text value"
name5 = number
[section2]
name6 = "text value"
...

The default is to read /etc/pukcab.conf then ~/.pukcabrc (which means that this user-defined file can override values set in the global configuration file).

Both client and server use the same configuration file format and location, only the values determine the client or server role (a client will have a server parameter set).

Notes

Server

The pukcab server contains the data files for all clients (in the vault) and a database of all backup sets (the catalog).

server configuration
parameter/section type default description
user text none user name pukcab will run under (mandatory)
vault text "vault" folder where all archive files will be created
catalog text "catalog.db" name of the catalog database
maxtries number 10 number of retries in case of concurrent client accesses
web text none auto-start the web interface on [host]:port (cf. listen)
webroot text none base URI of the web interface
[expiration] section specify expiration of standard schedules
daily number 14 retention (in days) of daily backups
weekly number 42 retention (in days) of weekly backups
monthly number 365 retention (in days) of monthly backups
yearly number 3650 retention (in days) of yearly backups

Notes

Example

; all backups will be received and stored by the 'backup' user
user="backup"
vault="/var/local/backup/vault"
catalog="/var/local/backup/catalog.db"
; keep daily backups longer (4 weeks instead of 2)
[expiration]
daily=28

Scheduling expiration

This task should be run every day, preferably when the system is idle (or at least, not receiving backups from clients).

Use cron to schedule pukcab expire to run daily.

On many systems (most Linux distributions), you can also create a script in /etc/cron.daily/pukcab-expire with the following content:

#!/bin/sh

exec pukcab expire

Client

The client configuration mainly focuses on what to include in the backup and what to exclude from it.

client configuration
parameter type default description
user text none user name to use to connect (mandatory)
server text none backup server (mandatory)
port number 22 TCP port to use on the backup server
command text "pukcab" command to use on the backup server
include list OS-dependent what to include in the backup
exclude list OS-dependent what to exclude from the backup
tar text "tar" tar command to use to restore files

including / excluding items

When taking a backup, pukcab goes through several steps to determine what should be backed up

  1. get all mounted filesystems
  2. include everything that is listed in include
  3. exclude everything that is listed in exclude

To select stuff to be included or excluded, you can use the following formats:

include/exclude filters
format matches examples
type mounted filesystems of that type "ext4", "btrfs", "procfs", "tmpfs", "hfs"
/path path and anything under it "/usr/tmp", "/var/tmp", "/tmp"
pattern files matching pattern8 ".*.swp", "*.part", "*.tmp"
./name directories containing something named name "./.nobackup"

Example

user="backup"
server="backupserver.localdomain.net"

Scheduling backups

Use cron to schedule pukcab backup to run whenever you want to take backups.

For daily backups, you can often just create a script in /etc/cron.daily/pukcab with the following content:

#!/bin/sh

exec pukcab backup

OS-dependent defaults

pukcab tries to apply “sane” defaults, especially when taking a backup. In particular, it will only attempt to backup “real” filesystems and skip temporary files or pseudo-filesystems.

Under Linux, there are many exclusions caused by the extensive use of pseudo-filesystems.

Linux defaults
parameter default value
include [ "ext2", "ext3", "ext4", "btrfs", "xfs", "jfs", "vfat" ]
exclude [ "/proc", "/sys", "/selinux", "tmpfs", "./.nobackup" ]

For Mac OS X, the list of included filesystems is much shorter (it currently includes just the default filesystem, HFS).

Mac OS X defaults
parameter default value
include [ "hfs" ]
exclude [ "devfs", "autofs", "afpfs", "./.nobackup" ]

Usage

Synopsis

pukcab command [ options … ] [ files … ]

available commands
backup, save take a new backup
config, cfg display pukcab’s configuration
continue, resume continue a partial backup
delete, purge delete a backup
expire apply retention schedule to old backups
history, versions list history for files
info, list list backups and files
ping, test check server connectivity
register register to backup server
restore restore files
summary,dashboard display information about backups
vacuum vault and catalog clean-up
verify, check verify files in a backup
web starts the built-in web interface

backup

The backup command launches a new backup:

Syntax

pukcab backup [ –full ] [ –name=name ] [ –schedule=schedule ]

Notes

config

The config command displays the current configuration.

Syntax

pukcab config

continue

The continue command continues a previously interrupted backup.

Syntax

pukcab continue [ –name=name ] [ –date=date ]

Notes

delete

The delete command discards the backup taken at a given date.

Syntax

pukcab delete [ –name=name ] [ –date=date ]

Notes

expire

The expire command discards backups following a given schedule which are older than a given age (or date).

Standard retention schedules have pre-defined retention periods:

default retention schedules
schedule retention period
daily 2 weeks
weekly 6 weeks
monthly 365 days
yearly 10 years
Syntax

pukcab expire [ –name=name ] [ –schedule=schedule ] [ –age=age ] [ –keep=keep ]

Notes

history

The history command shows the different versions stored in backups for given files. Backup sets can be filtered by name and/or date and files.

Syntax

pukcab history [ –name=name ] [ –date=date ] [ FILES … ]

Notes

info

The info command lists the backup sets stored on the server. Backup sets can be filtered by name and/or date and files.

Syntax

pukcab info [ –short ] [ –name=name ] [ –date=date ] [ FILES … ]

Notes

ping

The ping command allows to check connectivity to the server.

Syntax

pukcab ping

Notes

register

The register command registers a client’s SSH public key to the server.

Syntax

pukcab register

Notes

restore

The restore command restores files as they were at a given date.

Syntax

pukcab restore [ –in-place ] [ –directory=directory ] [ –name=name ] [ –date=date ] [ FILES … ]

Notes

summary

The summary command lists information about the backup sets stored on the server. Backup sets can be filtered by name.

Syntax

pukcab summary [ –name=name ]

Notes

vacuum

The vacuum command initiates clean-up of the catalog and vault to save disk space.

Syntax

pukcab vacuum

Notes

verify

The verify command reports files which have changed since a given date.

Syntax

pukcab verify [ –name=name ] [ –date=date ] [ FILES … ]

Notes

web

The web command starts the built-in web interface.

Syntax

pukcab web [ –listen=[host]:port ] [ –[root]=URI ]

Notes

Options

pukcab is quite flexible with the way options are provided:

This means that the following lines are all equivalent:

pukcab info -n test
pukcab info -n=test
pukcab info --n test
pukcab info --n=test
pukcab info -name test
pukcab info -name=test
pukcab info --name test
pukcab info --name=test

General options

The following options apply to all commands:

option description
-c, --config[=]file specify a configuration file to use
-F, --force[=true] ignore non-fatal errors and force action
-v, --verbose[=true] display more detailed information
-h, --help display online help

date

Dates are an important concept for pukcab.

All backup sets are identified by a unique numeric id and correspond to a set of files at a given point in time (the backup id is actually a UNIX timestamp). The numeric id can be used to unambiguously specify a given backup set but other, more user-friendly formats are available:

Syntax

--date[=]date

-d date

Examples

directory

Change to a given directory before restoring entries from the backup.

Syntax

--directory[=]directory

-C directory

Default value

none (i.e. extract to the current directory)

full

Forces a full backup: pukcab will send all files to the server, without checking for changes.

Syntax

--full[=true]

--full=false

-f

Default value

false

in-place

Change to the root of the filesystem (/) before restoring entries from the backup. This has the effect of restoring the files in-place, overwriting current files.

Syntax

--in-place[=true]

--in-place=false

--inplace[=true]

--inplace=false

Default value

false (i.e. extract to the current directory)

keep

When expiring data, keep at least a certain number of backups (even if they are expired).

Syntax

--keep[=]number

-k number

Default value

3

listen

Force the built-in web server to listen for connections on a different address/port.

Syntax

--listen[=][host]:port

-l [host]:port

Default value

localhost:8080

name

In pukcab, a name is associated with each backup when it’s created. It is a free-form text string.

Syntax

--name[=]name

-n name

Default value

current host name (output of the hostname command)

schedule

In pukcab, a retention schedule is associated with each backup when it’s created and is used when expiring old backups. It is a free-form text string but common values include daily, weekly, monthly, etc.

Syntax

--schedule[=]schedule

-r schedule

Default value

(the default value depends on the current day)

daily from Monday to Saturday

weekly on Sunday

monthly on the 1st of the month

yearly on 1st January

short

Display a more concise output.

Syntax

--short[=true]

--short=false

-s

Default value

false

Files

File names can be specified using the usual shell-like wildcards * (matches any number of characters) and ? (matches exactly one character). The following conventions apply:

Examples

Examples

  1. Launch a new backup - default options
[root@myserver ~]# pukcab backup
[root@myserver ~]#
  1. Launch a new backup - verbose mode
[root@myserver ~]# pukcab backup --verbose
Starting backup: name="myserver" schedule="daily"
Sending file list... done.
New backup: date=1422549975 files=309733
Previous backup: date=1422505656
Determining files to backup... done.
Incremental backup: date=1422549975 files=35
Sending files... done
[root@myserver ~]#
  1. Verify last backup - default options
[root@myserver ~]# pukcab verify
Name:     myserver
Schedule: daily
Date:     1427941113 ( 2015-04-02 04:18:33 +0200 CEST )
Size:     1.6GiB
Files:    50350
Modified: 10
Deleted:  0
Missing:  0
[root@myserver ~]#
  1. Verify last backup - verbose mode
[root@myserver ~]# pukcab verify --verbose
Name:     myserver
Schedule: daily
Date:     1427941113 ( 2015-04-02 04:18:33 +0200 CEST )
m /var/lib/chrony
M /var/lib/chrony/drift
M /var/log/cron
M /var/log/journal/5331b849b3844782aab45e85bd890883/system.journal
M /var/log/journal/5331b849b3844782aab45e85bd890883/user-1001.journal
M /var/log/maillog
M /var/log/messages
M /var/log/secure
M /var/spool/anacron/cron.daily
m /var/tmp
Size:     1.6GiB
Files:    50350
Modified: 10
Deleted:  0
Missing:  0
[root@myserver ~]#
  1. Find and recover a deleted file

Let’s pretend we want to recover a source RPM for netatalk that was deleted a while ago…

[root@myserver ~]# pukcab history netatalk\*.src.rpm
1422764854 myserver monthly Sun Feb 1 05:38
-rw-rw-r--  support support   1.8MiB Oct 30 17:30 /home/support/Downloads/netatalk-3.1.6-0.0.4.fc21.src.rpm
-rw-rw-r--  support support   1.7MiB Dec  2 19:59 /home/support/Downloads/netatalk-3.1.7-0.1.fc21.src.rpm

1424572858 myserver weekly Sun Feb 22 03:59

1425177758 myserver monthly Sun Mar 1 03:59

1425782947 myserver weekly Sun Mar 8 04:16

1426387616 myserver weekly Sun Mar 15 04:39

1426817749 myserver daily Fri Mar 20 03:31

1426904886 myserver daily Sat Mar 21 04:24

1426990487 myserver weekly Sun Mar 22 03:28

1427076410 myserver daily Mon Mar 23 04:00

1427165785 myserver daily Tue Mar 24 04:42

1427249388 myserver daily Wed Mar 25 03:24
[root@myserver ~]#

We found it! Let’s restore it in-place

[root@myserver ~]# pukcab restore -d 1422764854 -C / netatalk-3.1.7-0.1.fc21.src.rpm
[root@myserver ~]# cd /home/support/Downloads
[root@myserver ~]# ls -l netatalk-3.1.7-0.1.fc21.src.rpm
-rw-rw-r-- 1 support support 1804762 Dec  2 19:59 netatalk-3.1.7-0.1.fc21.src.rpm
[root@myserver ~]#

Frequently Asked Questions

Client FAQ

Is there a Windows client?

No, Windows is currently unsupported. Porting to Windows would require a significant effort and isn’t in the plans. This may change, though.

My first backup is taking forever! What should I do?

Wait. Another option is to make sure you didn’t forget to exclude useless or volatile data like * big Downloads folders * caches (Firefox, Safari, Thunderbird tend to keep gigabytes of throw-away data) * backups * temporary files you forgot to delete

My first backup is still taking forever! What should I do?

If necessary, you can interrupt it and continue later (pukcab will think a bit and restart where it was interrupted). Once the first backup is complete, you can take a second one and get rid (with delete) of the first one as many files may have changed during such a long backup.

Server FAQ

Is there a Windows server?

No, and there problably never will. If you’re seriously considering trusting a Windows server with your most precious data, we humbly suggest reconsidering your backup strategy.

Which filesystem should I use for the catalog? Can I use a network filesystem?

No, it must be stored on a local filesystem. You will need a fast filesystem able to deal with potentially big files (several gigabytes are not uncommon) that will be created and removed on the fly. For stability and performance reasons, you should prefer native filesystems, do NOT use NTFS, FAT or FUSE-based filesystems.

Which filesystem should I use for the vault? Can I use a network filesystem?

Yes, the vault can be on a remote filesystem. You will need a fast filesystem able to deal with potentially big files and, more importantly, with many files (often thousands and thousands) in the same directory. For that reason, do NOT use NTFS, FAT but you can use FUSE-based filesystems if they don’t put a limit on the number of files.

What are these catalog.db-wal and catalog.db-shm files? Can I remove them?

Short answer: don’t, you would lose backups!

These files are used to ensure safe concurrent access to the catalog to multiple pukcab instances. They are created and deleted automatically, there is no need for you to worry about them.
What is this catalog.db~ file? Can I remove it?

Short answer: you can, but it’s not recommended.

This file is an automatic backup of your catalog that is created right after each expire command. It may therefore be slightly obsolete but it can be used for recovery in case the live catalog gets destroyed/corrupted.
But catalog.db-wal is becoming huge! Can I shrink it?

Short answer: it will shrink when pukcab is done with what it is doing, or after the next expire command.

Depending of the number and length of concurrent operations, pukcab may make heavy use of this working file. You can reduce its maximum size by limiting the number of concurrent operations you run (i.e. you can serialise the backup commands).
If that doesn’t help, you can force-clean it by using vacuum
If that still doesn’t help, make sure no pukcab operation is running and issue the following command
sqlite3 catalog.db .schema

Internals

Logging

pukcab tries to generate useful log records by including easy-to-parse details into the events it sends to syslog, like in the following examples (from a Linux box):

Oct 21 08:25:40 server pukcab(newbackup)[16993]: Creating backup set: date=1445391440 name="client" schedule="daily"
Oct 21 08:36:19 client pukcab(backup)[27001]: Could not backup file="/var/log/httpd/access_log" msg="size changed during backup" name="client" date=1445391440 error=warn

The syslog APP-NAME field includes the command that generated the event: pukcab(command)

The rest of the event uses the following format: message [ [field=value] … ]

fields definition
field type unit description
date number backup date
duration number seconds execution time
elapsed number seconds total execution time
error token error severity (fatal / warn)
file text file name
files number total number of files
msg text human-readable error message
name text backup name
received number bytes amount of data received
schedule text backup schedule
sent number bytes amount of data sent
size number bytes total amount of data
type token backup type (incremental / full)

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NO WARRANTY

  1. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  2. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                 END OF TERMS AND CONDITIONS

  1. Basically, only configuration files and user data require disk space — that’s a blatant lie, the catalog uses disk space, too (but hopefully much less).

  2. This might change in the future, though.

  3. The main development platform is Fedora Linux x86-64.

  4. Some old Pentium III machines may misbehave.

  5. Linux users should prefer RPM packages or check if their distribution already includes pukcab.

  6. To rebuild pukcab, you will need a Go development environment (and some courage).

  7. pukcab will silently delete anything you may store there

  8. Shell patterns include at least one * or ? special character, with their usual meaning