Dar is a command-line software aimed to backup and archiving large live filesystems. It is a filesystem independent and cross platform 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.

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 disks, and since release 2.4.0 to tapes 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 full backup¹, incremental backup², differential backup³ and decremental backup⁴. 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).

Dar is able to be run on a live filesystem. 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.

Dar provides several hooks 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 suspending a database, and resuming it afterward).

Dar code has been split into two parts since its release 2.0.0, a command-line part and a library part called libdar. Dar is not a Graphical User Interface it is only a command-line tool, but thanks to the libdar library, many external tool rely on libdar and can manipulate dar archives at a more abstracted level with other interfaces than the shell command-line.

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).

Dar can be used through ssh for remote backups. It may also make used of so called "isolated catalogue" 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.

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:

archive creation (backing up all /usr directory) :
   dar -c my_backup -R / -g usr
  
archive restoration (restoring /usr in a alternate directory):
   dar -x my_backup -R /some/where/else

archive testing:
   dar -t my_backup

archive comparison with an existing filesystem:
   dar -d my_backup -R /

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 tutorial or mini-howto and for direct explanation of common questions by the FAQ, then, if you like or if you need, you can also look at the detailed man pages for a particular feature. You may also find some help on the dar-support mailing-list where a bit more than a hundred of subscribed users can help you.

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! ;-)

Follow an abstracted list of features is available if you want to know more about dar/libdar.

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).

To stay informed about new releases and security issues please subscribe to the Dar-news mailing-list. This is a read-only mailing-list with very low number of mail (usually less than ten a year).