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<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"><title>Dar's Documentation - General Presentation</title></head><body style="background-color: rgb(221, 221, 221); color: rgb(0, 0, 170);" alink="#ff0000" link="#0000ff" vlink="#000055">
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<tbody><tr><td style="vertical-align: top; width: 161px;"><a href="index.html"><img style="border: 0px solid ; width: 160px; height: 120px;" alt="Dar Documentation" src="dar_s_doc.jpg"></a><br>
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<td style="vertical-align: top;">
<h1 style="text-align: center;"><br>
</h1>
<h1 style="text-align: center;">PRESENTATION<br>
</h1>
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<h3 style="text-align: left;"><span style="text-decoration: underline;">1- General Presentation</span><br>
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<div style="text-align: justify;">Dar is a command-line software aimed to backup and archiving large live filesystems. It is a <span style="font-weight: bold;">filesystem independent</span> and <span style="font-weight: bold;">cross platform</span> tool.
But, Dar is not a boot loader, nor it is an operating system.
It does not create nor format partitions, but it can restore a full
filesystem into a larger or a shorter partition, from one partition to
several ones, (or the opposite from several to one partition), from a filesystem type to another
filesystem
type (ext2/3/4 to reiserFS for example), it can save and restore
hard-linked inodes (hard linked plain files, sockets, char/block
devices or even hard linked symlinks (!)), Solaris's Door files, it takes care of Posix Extended Attributes (Linux,
MacOS, ...). It can also detect and restore sparse files, even when the
underlying filesystem does not support them: it can restore a normal
file with large portions of zeroed bytes as a sparse file on another
filesystem that supports it, leading
to a gain in space requirement for the restoration but also for the archive size.<br>
<br>
From a filesystem, dar creates an archive, which may be split in a set of files (called slices) which size is user defined.
Dar archives are suitable to be stored on floppy, CD, DVD, usb key,
hard <span style="font-weight: bold;">disks</span>, and since release 2.4.0 to <span style="font-weight: bold;">tapes</span>
too. But no, dar itself cannot burn a DVD. Instead the user can give dar a
command to execute each time a slice is completed. Dar can perform <span style="font-weight: bold;">full backup</span><sup>1</sup>, <span style="font-weight: bold;">incremental backup</span><sup>2</sup>, <span style="font-weight: bold;">differential backup</span><sup>3</sup> and <span style="font-weight: bold;">decremental backup</span><sup>4</sup>.
It also records files that have been removed since the last backup
was
made, leading the restoration of a system to get the exact same state
it was at the time
of the differential/incremental/decremental backup (removing files that
ought to be removed, adding files that ought to be added and modifing files
as expected).<br>
<br>
Dar is able to be run on a<span style="font-weight: bold;"> live filesystem</span>.
It can detect when a file has changed while it was reading it, in that
case it is possible to ask dar to proceed to several retries to save such a
file. File that could not be saved properly (because they
changed during the backup and there is no more retry left) are flagged as "dirty" and are signaled at
restoration time. <br>
<br>
Dar provides <span style="font-weight: bold;">several hooks</span>
for the user to perform certain actions when some event are met. One
first hook let the user launch a command when a slice is completed
(for burning the slice to DVD for example). A second hook is available
for a given set of files or directories under backup, that let the user do some action
before and after saving that file or directory (like <span style="font-weight: bold;">suspending
a database</span>, and resuming it afterward).<br>
</div>
<br>
<div style="text-align: justify;">
Dar code has been split into two parts since its release 2.0.0, a command-line part and a library part called <span style="font-weight: bold;">libdar</span>. Dar is not a Graphical User Interface it is only a command-line tool, but thanks to the libdar library, many <a href="#external_tools">external tool</a> rely on libdar and can manipulate dar archives at a more abstracted level with other interfaces than the shell command-line.<br>
<br>
libdar may be linked against libz, libz2 and liblzo to provide gzip,
bzip2 and lzo compression. It can also be linked against libgcrypt to
provide strong encryption (blowfish, twofish, aes256, serpent256,
camellia256).<br>
<br>
Dar can be used through ssh for remote backups. It may also make used of so called "isolated <span style="font-style: italic;">catalogue</span>"
which is a small file containing the table of contents (or catalog) of
a given archive. These can be used as base for a differential,
incremental or decremental backup, and can also be used as backup of
the table of content of the original archive if that one get corrupted.<br>
<br>
While dar/libdar provide a lot of features we will not mention here,
you can use dar without having any knowledge of all of them. In its
most simple form, dar can be used only with few options, here follows
some example of use, that should not need additional explanations:<br>
<br>
archive creation (backing up all /usr directory) :<br>
<code> dar -c my_backup -R / -g usr<br>
<br>
</code>archive restoration (restoring /usr in a alternate directory):<code><br>
</code><code> dar -x my_backup -R /some/where/else<br>
<br>
</code>archive testing:<code><br>
</code><code>dar -t my_backup<br>
<br>
</code>archive comparison with an existing filesystem:<code><br>
</code><code> dar -d my_backup -R /</code><br>
<br>While
a big effort has been made on documentation, it must not lead you to
think that you have to read it all to be able to use dar: most needs
are covered by the <a href="Tutorial.html">tutorial</a> or <a href="mini-howto/index.html">mini-howto</a> and for direct explanation of common questions by the <a href="FAQ.html">FAQ</a>, then, if you like or if you need, you can also look at the
detailed <a href="man/index.html">man pages</a> for a particular feature. You may also find some help
on the <a href="http://lists.sourceforge.net/lists/listinfo/dar-support">dar-support mailing-list</a> where a bit more than a hundred of
subscribed users can help you. <br>
<br>
Dar's documentation is big because it also includes all that may
be useful to know how to use libdar, which is intended for developpers of
external application relying on this library. For those even more
curious there is also the documentation about dar's internals, libdar's
structure, archive format, which can ease the understanding of the
magic that makes all this working, and give a better understanding of
dar/libdar code, which is written in C++. But, no, you do not need to
read all this to just use dar! ;-)<br>
<br>Follow an <a href="Features.html">abstracted list of features</a> is available if you want to know more about dar/libdar.<br>
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<div style="text-align: left;">
<h3><span style="font-weight: bold; text-decoration: underline;"><a name="external_tools"></a>2 - Known Projects that rely
on dar or libdar</span></h3>
<h3><span style="font-weight: bold; text-decoration: underline;"></span></h3>
<span style="font-weight: bold; text-decoration: underline;">
<br>
</span></div>
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<span style="text-decoration: underline; font-weight: bold;"></span>
<ul>
<li style="text-align: justify;"><a href="http://www.boomerangsworld.de/cms/avfs/extfs?lang=en">AVFS</a> is virtual file system layer for transparently accessing the content
of archives and remote directories just like local files.</li>
<li style="text-align: justify;"><a href="http://dargui.sourceforge.net/">DarGUI</a> by Malcolm Poole is a front-end to dar providing simple and graphical access to the main features of dar.</li>
<li style="text-align: justify;"><a href="http://kdar.sourceforge.net/">kdar</a> is a KDE-3
Graphical User Interface to dar made by Johnathan Burchill </li>
<li style="text-align: justify;"> <a href="http://sarab.sourceforge.net/">SaraB</a>:
Schedule
And
Rotate Automatic Backups - by Tristan Rhodes. SaraB works with DAR to
schedule and rotate backups. Supports the Towers of Hanoi,
Grandfather-Father-Son, or any custom backup rotation strategy.</li>
<li style="text-align: justify;"><a href="http://sourceforge.net/projects/baras">Baras</a> by Aaron D.
Marasco it a rewriting in Perl of SaraB.</li>
<li style="text-align: justify;"><a href="http://lazybackup.sourceforge.net/">Lazy Backup</a> by Daniel
Johnson. Lazy Backup is intended to be so easy even lazy people will do
their backups</li><li style="text-align: justify;">A Dar plugin has been made by
Guus Jansman for <a href="http://mail.gnome.org/archives/mc-devel/2006-April/msg00001.html">Midnight
commander</a> (mc)</li><li style="text-align: justify;"><a href="https://wiki.ubuntu.com/HomeUserBackup">HUbackup</a> : Home User
backup<br>
</li><li style="text-align: justify;"><a href="http://darbinding.sourceforge.net/">Python Bindings</a> by
Wesley Leggette</li><li style="text-align: justify;"><a href="http://www.xsteve.at/prg/emacs/dar.html">Disk archive interface for Emacs</a> by <a href="http://www.xsteve.at/">Stefan Reichör</a></li><li style="text-align: justify;"><a href="http://www.artica.fr/"></a><a href="http://www.rgrjr.com/linux/backup.pl.html">backup.pl</a> script, creates and verifies a backup using dump/restore or using dar<br>
</li>
</ul>
<div style="text-align: justify;">
If a project you like is missing, you are welcome to contact me for it to be referred here (see the AUTHOR
document in the source package).</div>
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<div style="text-align: left;">
<h3><a name="limitations"></a><span style="font-weight: bold; text-decoration: underline;">3 - Limitations</span></h3>
<table style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;" border="0" cellpadding="2" cellspacing="2">
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<td style="vertical-align: top;">Dar has some limitations, they are details <a href="Limitations.html">here</a>.<br>
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<br>
<h3><a name="dar_news"></a><span style="font-weight: bold; text-decoration: underline;">4 - </span><span style="text-decoration: underline;">Staying informed of dar/libdar's events</span></h3>
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<div style="text-align: justify;">To stay informed about new releases and security issues please
subscribe to the <a href="https://lists.sourceforge.net/lists/listinfo/dar-news">Dar-news</a> mailing-list. This is a read-only mailing-list with very low number of mail (usually less than ten a year).<br>
<br>
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<div style="text-align: justify;"><font size="-1"><sup>1</sup> <span style="text-decoration: underline;">Full backup:</span>
A full backup is a backup of a full filesystem or of a subset of files
where, for each file, the archive contains all the inode information
(ownership, permission, dates, etc.) file's data and eventually file's
Extended Attributes.<br>
<sup>2</sup> <span style="text-decoration: underline;">Differential backup:</span>
A differential backup is based on a full backup. It contains only the
data and Extended Attributes of files that changed since the full
backup was made. It also contains the list of files that have been
removed since the full backup was made. For files that did not change,
it contains only the inode information. The advantage is that the
backup process is much faster, the space required is also much lower.
The drawback is that you need to restore the full backup first, then
the differential backup to get the last saved state of your system.<br>
</font>
<div style="text-align: justify;"><font size="-1"><sup>3</sup> <span style="text-decoration: underline;">Incremental backup:</span>
An incremental backup is essentially the same thing as a differential
backup. Some make a difference, I do not. The only point I see is that
the incremental backup is not based on a full backup but on a
differential backup or on another incremental one.<br>
</font></div>
</div>
<div style="text-align: justify;"><font size="-1"><sup>4</sup> <span style="text-decoration: underline;">Decremental backup:</span>
A decremental backup is a backup method in which the most recent backup
is a full backup, while the oldest backup are a difference compared to
that full backup. The advantage of such type of backup is the you can
restore easily your system in the last state it had using only the last
backup. And, if you want to restore it in the state it had some time before, then you can
restore the last backup (full backup), then the previous archive
(a decremental backup) and so on. As you most usually want to restore the
system in its last available state, this makes restoration much more
easy compared to doing incremental backups. However, this suffer from a
important drawback, which is that you need to transform the last backup
into a decremental backup when comes the time to make another backup.
Then you have to remove the former full backup and replace it by its
decremental version.</font><br>
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