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% Pukcab User's Guide % % March 2015

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 system^[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).].

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:

  • just run pukcab backup every night on your systems
  • full-system backups should be preferred, thanks to sensible OS-dependent default exclusions
  • automatic daily/weekly/monthly/yearly retention policies should keep enough backups around

Features

  • lightweight (just 1 binary to be installed on both the client and the server)
  • easy to install (only 1 username with SSH connectivity is required to set up a server)
  • flexible configuration
  • sensible defaults
  • automatic retention schedules
  • incremental/full backups
  • data de-duplication
  • data compression
  • (optional) web interface

Requirements

pukcab was written with UNIX-like operating systems in mind, it is therefore currently unsupported on Microsoft Windows^[This might change in the future, though.].

pukcab has been tested on the following operating systems and platforms^[The main development platform is Fedora Linux x86-64.]:

  • Linux 4.x on 64-bit Intel or AMD processors
  • Linux 4.x on 32-bit Intel or AMD processors^[Some old Pentium III machines may misbehave.]
  • Linux 3.x on 32-bit ARM processors
  • Mac OS X on 64-bit Intel processors

Backup server

To run a pukcab backup server, you will need:

  • SSH server
  • dedicated user (recommended)
  • disk space
  • scalable filesystem
  • enough memory or swap space (running without swap space is not recommended)

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.

  • SSH client
  • functional tar command (tested with GNU tar, should work with BSD (libarchive) tar and Jörg Schilling's star). Caution: the tar command of BusyBox is known to have issues that will prevent it from restoring files.
  • root access (if you want to backup files other than yours)

Installation

Just copy the pukcab binary1 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 Source2

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

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

  • sudo yum install pukcab-server
  • sudo yum install pukcab-client

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

  • text values must be enclosed in "
  • lists of values are enclosed in [ and ] with comma-separated items

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

  • vault and catalog paths can be absolute (starting with /) or relative to user's home directory.
  • the vault folder must be able to store many gigabytes of data, spread over thousands of files
  • the catalog database may become big and must be located in a folder where user has write access
  • the vault folder must not be used to store anything^[pukcab will silently delete anything you may store there] else than pukcab's data files; in particular, do NOT store the catalog there

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 pattern3 ".*.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:

  • creates a new backup set (and the corresponding date/id) on the backup server
  • builds the list of files to be backed-up, based on the include/exclude configuration directives
  • sends that list to the backup server
  • computes the list of changes since the last backup (if --full isn't specified)
  • sends the files to be includes in the backup
  • closes the backup

Syntax

: pukcab backup [ --full ] [ --name=name ] [ --schedule=schedule ]

Notes

  • the name and schedule options are chosen automatically if not specified
  • interrupted backups can be resumed with the continue command
  • unless forced, the command will fail if another backup for the same name is already running

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

  • the name option is chosen automatically if not specified
  • the date option automatically selects the last unfinished backup
  • only unfinished backups may be resumed

delete

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

Syntax

: pukcab delete [ --name=name ] [ --date=date ]

Notes

  • the name option is chosen automatically if not specified
  • the date must be specified, unless --force is used
  • all backups for a given name will be deleted if no date is specified (--force must be used in that case)

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

  • if date is specified, the command lists only history after that date
  • on server, if name is not specified, the command lists all backups, regardless of their name

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

  • if date is specified, the command lists only details about the corresponding backup
  • on server, if name is not specified, the command lists all backups, regardless of their name
  • verbose mode lists the individual files

ping

The ping command allows to check connectivity to the server.

Syntax

: pukcab ping

Notes

  • verbose mode displays detailed information during the check

register

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

Syntax

: pukcab register

Notes

  • to register to the backup server, pukcab will ask for the dedicated user's password (set on the server)
  • verbose mode displays detailed information during the registration

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

  • the name option is chosen automatically if not specified
  • the date option automatically selects the last backup
  • this operation currently requires a working tar system command (usually GNU tar)
  • --in-place is equivalent to --directory=/

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

  • on server, if name is not specified, the command lists all backups, regardless of their name

vacuum

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

Syntax

: pukcab vacuum

Notes

  • can only be run on the server
  • the clean-up may take a while and delay new backups

verify

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

Syntax

: pukcab verify [ --name=name ] [ --date=date ] [ FILES ... ]

Notes

  • the name option is chosen automatically if not specified
  • the date option automatically selects the last backup if not specified

web

The web command starts the built-in web interface.

Syntax

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

Notes

  • by default, pukcab listens on localhost on port 8080
  • available features depend on the local system's role (client or server)

Options

pukcab is quite flexible with the way options are provided:

  • options can be provided in any order
  • options have both a long and a short (1-letter) name (for example, --name is -n)
  • options can be prefixed with 1 or 2 minus signs (--option and -option are equivalent)
  • --option=value and --option value are equivalent (caution: = is mandatory for boolean options)

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:

  • a duration in days (default when no unit is specified), hours, minutes is interpreted as relative (in the past, regardless of the actual sign of the duration you specify) to the current time
  • a human-readable date specification in YYYY-MM-DD format is interpreted as absolute (00:00:00 on that date)
  • now or latest are interpreted as the current time
  • today is interpreted as the beginning of the day (local time)

Syntax

: --date[=]date

: -d date

Examples

  • --date 1422577319 means on the 30th January 2015 at 01:21:59 CET
  • --date 0, --date now and --date latest mean now
  • --date today means today at 00:00
  • --date 1 means yesterday same time
  • --date 7 means last week
  • --date -48h and --date 48h both mean 2 days ago
  • --date 2h30m means 2 hours and 30 minutes ago
  • --date 2015-01-07 means on the 7th January 2015 at midnight

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:

  • file names starting with a slash ('/') are absolute
  • file names not starting with a slash ('/') are relative
  • specifying a directory name also selects all the files underneath

Examples

  • /home includes /home/john, /home/dave, etc. and all the files they contain (i.e. all users' home directories)
  • *.jpg includes all .jpg files (JPEG images) in all directories
  • /etc/yum.repos.d/*.repo includes all repositories configured in Yum
  • /lib includes /lib and all the files underneath but not /usr/lib, /var/lib, etc.

Examples

(@) Launch a new backup - default options

[root@myserver ~]# pukcab backup
[root@myserver ~]#

(@) 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 ~]#

(@) 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 ~]#

(@) 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 ~]#

(@) 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
  • replace catalog.db by your catalog's path
  • you may need to install SQLite
  • this command must be run as the pukcab user on the server
  • this command will (probably) take very long and block any backup until it has completed

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)

License

                GNU GENERAL PUBLIC LICENSE
                   Version 2, June 1991

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the Program is not required to print an announcement.)

These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

  1. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:
a) Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,

b) Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,

c) Accompany it with the information you received as to the offer
to distribute corresponding source code.  (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)

The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

  1. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

  2. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

  3. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

  4. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

  1. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

  2. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

  1. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

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

Footnotes

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

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

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