Checkit is a file integrity tool for Linux and Unix systems.

Checkit Copyright (C) 2014 Dennis Katsonis

LICENSE INFO
------------

Checkit is free software distributed under the GNU GPL.  See below for
copyright for CRC64.

WHAT THIS PROGRAM DOES:
-----------------------

Checksum adds additions data assurance capabilities to filesystems
which support extended attributes.  Checkit allows you to detect any
otherwise undetected data integrity issues or file changes to any
file.  By storing a checksum as an extended attribute, checkit
provides an easy way to detect any silent data corruption, bit rot or
otherwise modified error.

This was inspired by the check-summing that is performed by
filesystems like BTRFS and ZFS.  These filesystems ensure data
integrity by storing a checksum (CRC) of data and checking read data
against the checksum.  With mirroring of data, they can silently heal
the data should an error be found.

This program does not duplicate this ability, but offers rudimentary
checksum abilities for other filesystems.  It simply calculates a
checksum and stores the checksum with the file.  It can then be later
used to verify the checksum against the data.  Any data corruption of
file changes would result in a failed check.

WHY IT WAS CREATED:
-------------------

Moving data from disk to disk, or leaving data on the disk, leaves a
very small possibility of silent data corruption.  While rare, the
large amounts of data being handled by drives make silent corruption a
real possibility.  While BTRFS and ZFS can handle this, other
filesystems can't.  This program was created to add an ability to
detect (but not fix) issues.  With the ability to detect, you can
easily find out whether a copy or extract operation occurred
perfectly, or whether there has been bit rot in the file.

Backups provide point of reference, but comparison isn't very
efficient, as it involves reading two files.  Using a CRC, you only
need to read the file once, even after a copy operation to determine
whether the file is OK.  Also, should the file be different from the
backup, which copy is OK, the backup or the original?  Checkit will
let you know whether it is the backup or original which has changed.

There are other ways to do this.  You can use a cryptographic hash and
store a SHA-1 or MD5 or SHA-256 value in a separate file, or even use
GPG and digitally sign the file.  The problem is, that the value is
stored in a separate file, and doing directory recursion, or all files
of a particular type (i.e., all JPG's isn't as straightforward.  With
checkit, the CRC is stored as an extended attribute.  It remains as
part of the file, and can be copied or archived automatically with the
file.  No need for separate files to store the hash/checksum.

Checkit also has the ability to export this to a hidden file, and
import it back into an extended attribute.

DOWNLOAD:
---------

You can download the latest release here
http://boraxman.strangled.net/checkit/0.5.3/

Here is the source code

http://boraxman.strangled.net/checkit/0.5.3/checkit-0.5.3.tar.gz), which you can compile.

GPG signature for the above source package.
http://boraxman.strangled.net/checkit/0.5.3/checkit-0.5.3.tar.gz.asc
Signing key: D78BA4DD4AADF348

There are also ready to use packages for Fedora and RPM based distros

RPM for Fedora and RedHat Distros
http://boraxman.strangled.net/checkit/0.5.3/RPM/checkit-0.5.3-1.x86_64.rpm

Fedora dropped 32 bit support, and so have I.  The last version for Fedora 32 is below.

RPM for Fedora and RedHat Distros (32 bit)
http://boraxman.strangled.net/checkit/0.5.2/RPM/checkit-0.5.2-1.i686.rpm

SRPM
http://boraxman.strangled.net/checkit/0.5.2/RPM/checkit-0.5.2-1.src.rpm

Debian 12 package for 64 bit systems
http://boraxman.strangled.net/checkit/0.5.3/debian12/checkit_0.5.3-1_amd64.deb

Debian 12 package for 32 bit systems
http://boraxman.strangled.net/checkit/0.5.3/debian12/checkit_0.5.3-1_i386.deb


Debian 11 package for 64 bit systems
http://boraxman.strangled.net/checkit/0.5.3/debian11/checkit_0.5.3-1_amd64.deb

Debian 11 package for 32 bit systems
http://boraxman.strangled.net/checkit/0.5.3/debian11/checkit_0.5.3-1_i386.deb

Debian package for ARM systems (i.e., Raspbian)
http://boraxman.strangled.net/checkit/0.5.3/raspbian/checkit_0.5.3-1_armhf.deb

HOW TO USE:
-----------

Checkit calculates and stores the CRC as an extended attribute
(user.crc64) or as a hidden file.  The file must reside on a
filesystem which supports extended attributes (XFS, JFS, EXT2, EXT3,
EXT4, BTRFS, ReiserFS among others) to use the extended attribute
(recommended).

First, run checkit to store the CRC as an attribute, then at any time,
you can run checkit to check that the file data still matches the CRC.
If any of the files don't match, or the CRC is missing, checkit will
report it.  If you pass the "verbose" option, checkit will summarise
the files that didn't pass the checksum test at the end of the run.

Checkit allows you to determine whether the checksum is 'read only' or
'read write', using the -d and -u options.  A 'read only' checksum
will not be updated, unless the '-o' overwrite option is used.  This
way, the checksum is not inadvertantly updated when rerunning checkit
over it.  A 'read write' checksum can be updated, and can be used in
those cases where you want to rerun checkit over the file, and
recompute the checksum because of intended changes.  For the most
part, checkit is intended for files you want to remain static, such as
your precious family photos and movies, archives and such.

OPERATION:
----------

checkit [OPTION] [FILE]

Options:

-V      Print licence

-s      Calcuates and stores the checksum.

-c      Check file against stored checksum.

-v      Verbose.  Print more information.

-p      Display CRC64 checksum.

-x Remove stored checksum.  This simply deletes the extended
attribute.

-o Overwite existing checksum.  By default, checkit does not overwrite
an existing checkum. This option allows you to update the checksum,
should the file be deliberately altered).

-r      Recurse through subdirectories.

-e      Export CRC to a hidden file.

-i      Import CRC from a hidden file.

-d Disallow updating of CRC on this file (for files you do not intend
to change)

-u Allow CRC on this file to be updated (for files you intend to
change) [FILE] can include wildcards.

-m Force monochrome (disable colours).  By default, coloured output is
only used when the output device is a terminal.

Examples:

checkit -s -o picture.jpg ;Calculates checksum of picture.jpg and
overwrites old CRC64

checkit -s -r .  ;Processes current directory and all sub-directories
and files.

checkit -c -r pictures/ ;Check the entuie pictures directory. Checkit
will report whether all files are OK or not.

checkit \-d dissertation.txt ;Sets the CRC as read only.  Checkit will
NOT update the CRC if you try to store the checksum again.

checkit \-u dissertation.txt ;Setc the CRC as read write.  Checkit
will update the checksum if you run it with the -s option.

LIMITATIONS:
------------

As checkit doesn't repair files, you need to ensure that you have
backups of important data.  Checkit by default stores the CRC in an
extended attribute.

If the checksum is stored as an extended attribute, which is the
default, it will be lost if you transfer the file to a filesystem
which does not support extended attributes, or the method of copying
does not preserve them.  If you export the CRC, then the CRC can
travel with the file as long as you copy the CRC hidden file as well.

Checkit cannot detect changes and recompute the checksum without being
run manually, because it doesn't run in the background.  While having
a 'checkit' daemon, which can automatically update the checksum should
the file be changed is potentially useful, this is better done by
migrating to BTRFS or ZFS, which handles this more efficiently than
checkit ever could.

TODO:
-----

* Integration with file managers.

CRC64 routine.

The checksum routine is the crc-64-jones created by Salvatore
Sanfilippo.

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