This tutorial shows you how to backup your file system (partially or
totally) on ZIP drives (you can replace Zip by floppies, or USB key if you prefer) and most important, how to restore your system from scratch in case of hard disk failure (or other cataclysms).
GUI over libdar are nice to use, to backup once. Scripting using
dar is better as it can run in background and be scheduled every day,
this is a matter of taste. But you need a robust solution that works
also within a minimum environement to be able to restore your system.
Dar provides a lot a features at backup time (defining compression etc.),
thus a GUI or a script is welcome in this process, however only very
few are necessary at restoration time and in that situation, dar_static (the
statically linked version of dar) is to my point of view, the best
solution to use.
STEP 1: The FULL backup
We need first to make a full
backup, let's go:
The size of a zip drive is 100 MB,
*** here comes the option: -s 100M
This tells dar to not create a single backup file but to split it in
several files with a size of at most 100 Megabytes.
On your first ZIP drive we want to copy the dar binary outside the
backup to be able to restore it in case of hard disk failure, for
dar binary relies on several libraries which must also be available in
the rescue system or copied with the dar binary. But, if you don't want
to worry about needed libraries, there is a static version of dar which
only difference is that it has all required library included in it (thus it is a slightly larger binary). Its name is "dar_static
and its main reason of existence is to be placed beside backups in case
something goes wrong in your system. Note that dar_static is useless
for windows, you will always need the Cygwin
(You could also add man pages or a copy of this tutorial, if you are scared not to be able to
remember all the many feature of dar ;-) and find the -h option too
sparse). Note that all the dar documentation is available on the web. OK you need an
Internet access to read them.
This make the free space on the first ZIP floppy a bit smaller, I let
you make the substraction because this is subject to change from system
to system, but let's assume dar_static is less than 5 MB, thus the
initial slice should not exceed 95 MB
*** Here comes the option: -S 95M
(Note that '-s' is lowercase for all the slices, and '-S' is UPPERCASE
meaning the initial slice only).
We need to pause between slices to change the ZIP floppy when it is
*** here comes the option: -p -b
telling dar to pause before writing a new slice (-p) and to ring the
terminal bell (-b) when user action is needed.
We will compress data inside the backup
*** here comes the option: -z
default -z option uses gzip compression algorithm (bzip2, lzo, xz and some others are
also available). Optionally, if speed is more important than archive
size, you can degrade compression specifying the compression level :
-z1 for example.
Now, we want to backup the whole file system.
*** here comes the option: -R /
This tells dar that no files out of this directory tree will be saved
(here, it means that no files will be excluded from the backup, if no
filter is specified, see below) here "R" stands for "Root".
There are some files you probably don't want to backup like backup files
generated by emacs "*~" and .*~".
*** here comes the options: -X "*~" -X ".*~"
Note that you have to quote the mask for it not to be interpreted by
the shell, the -X options (X for eXclude) do not apply to directories, nor to path, they
just apply to filenames. (see also -I option (I for Include) in man page for more information)
Among these files are several sub-trees you must not save: the /proc
file system for example, as well as the /dev/pts and /sys . These are virtual
file systems, saving them would only make your backup bigger filled
with useless stuff.
*** here come the options: -P dev/pts -P proc -P sys
Note that path must be relative to -R option (thus no leading '/' must
be used) Unlike the -X/-I options, the -P option (P for "prune") can apply to a directory. If
a directory matches -P option, all its subdirectory will also be
excluded. note also that -P can receive wildcards, and they must be
quoted not to be interpreted by the shell:
for example. Lastly, -P can also be used to exclude a plain file (if
you don't want to exclude all files of a given name using -X option):
for example would only exclude joe's .bashrc file
not any other file, while -
would exclude any file of that name
including joe's file. (see also -g, -[, -] options in man page for more, as well as the "file selection in brief" paragraph)
More importantly we must not save the backup itself:
*** here comes the option: -P mnt/zip
assuming that your ZIP is mounted under /mnt/zip . We could also have
excluded all files of extension "dar" which are backup generated by dar using
, but this would have also exclude other dar archive from the
backup, which may not always fit your need.
Now, as we previously excluded save the /dev/pts /proc and /mnt/zip directories, we
would have to create these directory mount-points by hand at recovery
time to be able to mount the corresponding filesystems. But we can
using the -D option: it changes dar's behavior by not totally ignoring excluded directories
but rather storing them as empty.
*** here comes the option -D
thus at recovery time they will be generated automatically
Lastly, we have to give a name to this full backup. Let's call it
"linux_full" and as it is supposed to take place on the ZIP drive, its path
*** here comes the option: -c /mnt/zip/linux_full
Note that linux_full is not a complete filename, it is a "basename", on
which dar will add a number and an extension ".dar", this way the first
slice will be a file of name linux_full.1.dar located in /mnt/zip
Now, as we will have to mount and umount the /mnt/zip file system, we
must not have any process using it, in particular, dar current
directory must no be /mnt/zip so we change to / for example.
All together we follow this procedure for our example:
Put an empty ZIP floppy in the device, and mount it according to your
Copy the dar binary to the first zip drive (to be able to restore in case of
big problem, like a hard disk failure) and eventually man pages and/or this tutorial.
`which dar_static` /mnt/zip
then, type the following:
dar -c /mnt/zip/linux_full -s 100M -S 95M -p -b -z -R / -X
"*~" -X ".*~" -P dev/pts -P sys -P proc -P mnt/zip -D
that option order has no importance. Some options may be used
several times (-X, -I, -P) some others cannot (see man page for more).
When the first slice will be done, DAR will pause, ring the terminal and display a
message. You will have to unmount the floppy
eject and replace the floppy by
an empty new one and mount it
To be able to do that, you can swap to another virtual console pressing
ALT+F? keys (if under Linux), or open another xterm if under X-Windows, or suspend dar
by typing CTRL-Z and reactivating it after mounting/unmounting by
typing `fg' (without the quotes).
Then proceed with dar for the next slice, pressing the <enter> key.
Dar will label slices this way:
slice 1: linux_full.1.dar
slice 2: linux_full.2.dar
and so on.
That's it! We have finished the first step, it may take a long time
depending on the size of the data to backup. The following step
(differential backup) however can be done often, and it will stay fast
every time (OK, except if a big part of your system has changed, in
that case you can consider making another full backup).
Just a little check on the archive you've just made: suppose you want
to read the content of the backup you made, you would have
It is recommended to either check
the archive contents, or compare what's stored in it with the current
file system before relying on it:
This will check the whole archive, while it is recommended to first unmount and remount removable disk, this to flush the
cache. Else you may read data from cache (in memory) and do not detect
an error on you disk. dar -t cannot check a single slice, it checks
all the archive. If you need to check a single slice (for example after
burning it on CD) you can use the diff command : for example, you burn
the last completed slices on CD-R, but have just enough free space to
store one slice on disk. You can thus check the slice typing something
where 132 has to be replaced by the real slice number.
You can also add the --hash command when you create the archive (for example --hash md5
it will produce for each slice a small hash file named after the slice name
"linux_full.1.dar.md5", "linux_full.2.dar.md5", etc. Then using the
unix standard command "md5sum" you can check the integrity of the slice
md5sum -c linux_full.1.dar.md5
If all is ok for the slice on the zip disc (which is when diff does not complain or md5sum returns "OK"), you can delete the
slice from the hard disk (/tmp/slice.x.dar), and continue with dar.
Else, you will have to burn/write the slice on a new disk or retry on the same.
Instead of testing the whole archive you could also compare it with the just saved system:
/mnt/zip/linux_full -R /
will compare the archive with filesystem tree located at / . Same
remark as previously, it is recommended to first unmount and mount the
floppy to flush the system cache.
STEP 2: DIFFERENTIAL BACKUP
The only thing to add is the
base name of the backup we take as reference
*** here comes the option: -A /mnt/zip/linux_full
Of course, we have to choose another name for that new backup, let's call
*** here comes the option: -c /mnt/zip/linux_diff1
Last point: if you want to put the new backup at the end of the full
backup, you will have to change the -S option according to the
remaining space on the last disk. suppose the last slice of linux_full takes 34MB
you have 76MB available for the first slice of the differential backup
(and always 100MB for the following ones),
*** here comes the option: -S 76M
but if you want to put the backup on a new floppy, just forget the -S
here we also want to produce a hash file to test each slice integrity before removing it from hard disk:
*** here comes the option: --hash md5
All together we get:
/mnt/zip/linux_diff1 -A /mnt/zip/linux_full -s 100M -S 76M -p -b -z -R
/ -X "*~" -X ".*~" -P dev/pts -P proc -P mnt/zip -P sys -D --hash md5
only new point is that, just before effectively starting
to backup, dar will ask for the last slice of the
archive of reference (linux_full), then dar will pause (thanks to the
-p option) for you to change the disk and put the one where you want to
write the new backup's first slice, then pause again for you to change
the disk for the second slice and so on.
STEP 3: ENDLESS DIFFERENTIAL
You can make another
differential backup, taking linux_diff1 as reference, in this case you
would change only the following
/mnt/zip/linux_diff2 -A /mnt/zip/linux_diff1
could also decide to change of device, taking a 1'44MB floppy or a
CD-R ... or maybe rather something more recent and bigger if you
want, this would not cause any problem at all. After some time
you get many differential backup for a single full backup, you will
have to make a new full backups, depending on your available time for
doing it, or on your patient if one day you have to recover the whole
data after a disk crash: You would then have to restore the full
backup, then all the following differential backup up to the most
recent one. This requires more user intervention than restoring a
single full backup, all is a matter of balance, between the time it
takes to backup and the time it takes to restore.
Note, that starting release 1.2.0 a new command appeared that helps
restoring a small set of file from a lot a differential backup. Its
name is dar_manager. See at the end of this tutorial and the associated man page for
Another solution, is when you have too much differential backup, is to
make the next differential backup taking the last full_backup as
reference, instead of the last differential backup done. This way, it
will take less time than doing a full backup, and you will not have to
restore all intermediate differential backup. Some people make
difference between "incremental" backup and "differential" backup. Here
for dar, they look like the same, it just depends on the nature of the reference backup
Of course, a given backup can be used as reference for several
differential backup, there is no limitation in number nor in nature
(the reference can be a full of differential backup).
Yet another solution is to setup decremental backup, this is let you
have the full backup as the most recent one and the older ones as
difference from the backup done just after them... but nothing is
perfect, doing so takes much time than doing full backup at each step
but as less storage space as doing incremental backups. here too all is
a matter of choice, taste and use case.
STEP 4: RECOVER AFTER A DISK
Sorry, it arrived, your old
crashed. OK, you are happy because you have now a good argument to buy
the very fast and very enormous very lastest hard disk available. Usually,
you also cry because you have lost data and you will have to reinstall
all your system, that was working so well and for so long!
however the last backup you made is recent, then keep smiling! OK,
you have installed your new hard disk and configured you BIOS to it
(well at ancient time it was necessary do do something with the BIOS,
today you can forget it).
1. You first need to boot your new computer with the empty disk in order to restore your data onto it. For that there is Knoppix
or system rescue CD
that let you boot from CD or USB key. You don't
need to install something on your brand-new disk, just make partitions
and format them as you want (we will detail that below). You may even
change the partition layout add new ones or merge several into one:
what is important is that you setup each one with enough space to hold
the data to be restored in them: We suppose your new disk is /dev/hda
/dev/sga is your removable media drive (USB key, DVD device, ...) For
clarity, in the following we will assume it to be a set of USB keys, it
could be CD, DVD, or other disk you would do slightly the same.
2. Create the partition table as you wish, using
3. Format the partition which will receive your data, dar is filesystem
independent, you can use ext2 (as here in the example), ext3, ext4,
ReiserFS, Minix, UFS, HFS Plus, XFS, whatever is the Unix-like
filesystem you want, even if the backed up data did not reside on such
filesystem at backup time!
and record in a temporary file the UUID of the generated filesystem if
the /etc/fstab we will restore in the next steps rely in that instead
of fixed path (like /dev/hda1).
4. Additionally if you have created it, format the swap partition and also record the generated UUID if necessary
5. If you have a lot of file to restore, you can activate the swap
on the partition of your new hard drive:
6. Now we must mount the hard disk, somewhere.
mount -t ext2 /dev/hda1 /disk
would do the trick
6-alternative. If you want to restore your system over several partitions like
/usr /var /home and / , you must create the partitions, format them as seen above and then
create the directories that will be used as mounting point an mount the
partitions on these directories. For example if you have / , /usr ,
/var and /home partitions this would look like this:
/disk/usr /disk/var /disk/home
mount -t ext2 /dev/hda2 /disk/usr
mount -t ext2 /dev/hda3 /disk/var
mount -t ext2 /dev/hda4 /disk/home
If the boot system used does not already include dar/libdar (unlike
system rescue CD and Knoppix for example) we need to copy the dar
binary from a removable medium to your disk: insert the USB key
containing the dar_static binary to be able to freely change of key
mount -t ext2 /dev/sga /usb_key
cp /usb_key/dar_static /disk
/dev/sga points to your usb_key drive (run "dmesg" just after plugging
the key to know which device to use in place of the fancy /dev/sga). We
will remove dar_static from your new hard drive at the end of
8. Now we can restore the archive. The stuff has to go in /disk subdirectory
*** here comes the option: -R /disk
9. The process may be long, thus it might be useful to be noticed when
a user action is required by dar.
*** here comes the option: -b
note that -p option is not required here because if a slice is missing
dar will pause and ask you its number. If slice "0" is requested, it
means the "last" slice of the backup.
let's go restoring!
-x /usb_key/linux_full -R /disk -b
... and when the next USB key is needed,
then unplug it, plug the next one and mount it:
-t ext2 /dev/sga /usb_key
as previously, to do that either use an second
virtual console or suspend dar by CTRL-Z and awake it back by the 'fg'
command. Then press <enter> to proceed with dar
Once finished with the restoration of linux_full, we have to do the
same with any following differential/incremental backup. However, doing
so will warn you any time dar restores a more recent file (file
overwriting) or any time a file
that has been removed since the backup of reference, has to be removed
from file system (suppression). If you don't want to press the
<enter> key several thousand times:
*** here comes the option: -w
(don't warn). All file will be overwritten without warning.
All together it makes:
-x /usb_key/linux_diff1 -R /disk -b -w
Then any additional archive:
-x /usb_key/linux_diff2 -R /disk -b -w
/disk/dar_static -x /usb_key/linux... -R /disk -b -w
11. Finally, remove the dar binary from the disk:
12. modify the /etc/fstab with the new UUID you have recorded at step 4, 5 and eventually 6 bis.
13. Last, reinstall you original boot loader from the restored data:
If you still use lilo type:
If your boot loader is grub/grub2 type:
14. You can reboot you machine and be happy with you brand-new hard
disk with your old precious data on it:
In this operation dar will in particular restore sparse files and hard
linked inodes, thus you will have no drawback and even possibly better
space usage than the original filesystem as dar can even transparently
convert big plain files into smaller sparse files without any impact.
STEP 4(bis): recover only some
Gosh, you have remove a
file by error. Thus, you just need to restore it, not the rest of the
full and differential backups.
a) First method:
We could as previously, try all
archive starting from the full backup up to the most recent
differential backup, and restore just the file if it is present in the
/ -x /zip/linux_full -g home/denis/my_precious_file
This would restore only the file /home/denis/my_precious_file from the
OK, now we would also have to restore from all differential backup the
same way we did. Of course, this file may have changed since the full
/ -x /zip/linux_diff1 -g home/denis/my_precious_file
and so on, up to the last differential archive.
/ -x /zip/linux_diff29 -g home/denis/my_precious_file
b) Second method (more
We will restore our lost file,
starting from the most recent differential backup and *maybe* up to the
full backup. Our file may or may not be present in the a
differential archive as it may have changed or not since the previous
version, thus we have to check if our file is restored, using the -v
/ -x /zip/linux_diff29 -v -g home/denis/my_precious_file
If we can see a line like
Then we stops here, because we got the most recent backup version of our
lost file. Otherwise we have to continue with the previous
differential backup, up to the full backup if necessary. This
method has an advantage over the first one, which is not to have *in all
case* the need to use all the backup done since the full backup.
If you are lazy (as I am) on the other hand, have a look at dar_manager (at the
end of the tutorial)
OK, now you have two files to restore. No problem, just do the second
method but add -r option not to override any more recent file already
restored in a previous step:
/zip/linux_diff29 -R / -r -v -g home/denis/my_precious_file -g etc/fstab
Check the output to see if one or both of your files got restored. If
not, continue with the previous backup, up to the time you have seen
for each file a line indicating it has been restored. Note that the most
recent version of each files may not be located in the same archive,
thus you might get /etc/fstab restored from linux_diff28, and
/home/denis/my_precious_file restored at linux_diff27. In the case
/etc/fstab is also present in linux_diff27 it would not have been
overwritten by an older version, thanks to the -r option.
This option is very important when restoring more than one file using
the second method. Instead, in the first method is used (restoring first from
the full backup, then from all the following differential backups), -r
option is not so important because if overwriting occurs when you restore
lost files, you would only overwrite an older version by a newer.
Same thing here, even if you are not lazy, dar_manager can help you
a lots here to automate the restoration of a set of file.
ISOLATING A CATALOGUE
We have seen previously how to do differential backups. Doing
so, dar asks the last slice of the archive of reference. This operation
is required to read the table of contents (also known as "catalogue"
[this is a French word that means "catalog" in English, I will keep
this French word in the following because it is also the name of the
C++ class used in libdar]) which is located at the end of the archive
(thus on the last slice(s)). You have the possibility to isolate
(that's it to extract) a copy of this table of content to a small file.
This small file is quite exactly the same as a differential archive
that holds no data in it. Let's take an example with the full backup we
did previously to see how to extract a catalogue:
dar -C /root/CAT_linux_full -A /mnt/zip/linux_full
Note here that we used the UPPERCASE 'C' letter, by opposition the the
lowercase 'c' which is used for archive creation, here we just created
an isolated catalogue, which is usually a small archive. In addition,
you can use -z option to have it compressed, -s and -S option to have
it split in slices, -p option, -b option, but for an isolated catalogue
this is not often necessary as it is usually rather small. The only
thing we have seen for backup that you will not be able to do for
isolation is to filter files (-X, -I, -g, -P, -[ and -] option are not
available for that operation).
So what, now we have our extracted catalogue, what can we do with it? Two things:
we can use the extracted catalogue in place of the archive, as
reference for a differential backup. No need to manipulate the old zip
disks, you can store the last's backup isolated catalogue on your hard
disk instead. If we had used an isolated catalogue in the previous
examples, we would have built our first differential backup this way
(note that here we have chose to use the CAT_ prefix to indicate that
the archive is an isolated catalogue, but the choice is yours to label
isolated catalogue the way you want):
dar -c linux_diff1 -A /root/CAT_linux_full ... (other options seen above stay the same)
we can use the isolated catalogue as backup of the internal catalogue
if it get corrupted. Well to face to data corruption the best solution
ever invented is Parchive
, an autonomous program that builds parity
file (same mechanism as the one used for RAID disks) for a given file.
Here we can use Parchive to create a parity file for each slice. So,
assuming you lack Parchive, and that you failed reading the full backup
because the zip disk is corrupted in the part used by the internal
catalogue, you can use an isolated catalogue as rescue:
dar -x linux_full -A /root/CAT_linux_full ...
dar -d linux_full -A /root/CAT_linux_full ...
dar -t linux_full -A /root/CAT_linux_full ...
dar -l /root/CAT_linux_full
An isolated catalogue can be built for any type of archive (full,
differential or incremental archive, even for an already isolated
catalogue, which I admit is rather useless). You can also create an
isolated catalogue at the same time you do a backup, thanks to the -@
dar -c linux_diff1 -A /mnt/zip/linux_full -@ CAT_linux_diff1 ... (other options...)
dar -c linux_full -@ CAT_linux_full ... (other options see above stay the same for backup)
This is know as "on-fly" isolation.
builds a database
your archive contents, to automatically restore the latest versions of
a given set of files. Dar_manager is not targeted to the restoration a
whole filesystem, the best ways to restore a whole filesystem has been
described above and do not use dar_manager. So let's use dar_manager to
restore a set of files. First, we have to create a "database" file :
This created a file "my_base.dmd" where dmd stands for Dar Manager
Database, but you are free to use any other extension.
This database is created empty. Each time you make a backup, may it be
full or differential, you will have to add its table of contents (aka "catalogue") to this
database using the following command:
-B my_base.dmd -A /mnt/zip/linux_full
This will add ("A" stands for "add") the archive contents to the base.
In some cases you may not have the archive available but its extracted
catalogue instead. Of course, you can use the extracted catalogue in
place of the archive!
-B my_base.dmd -A ~/Catalogues/CAT_linux_full
The problem however is that when dar_manager will need to recover a
file located in this archive it will try to open the
archive ~/Catalogue/CAT_linux_full for restoration, which does not contain any
data because it is just the catalogue of the archive.
No problem if you made this mistake, thanks to the -b option we can
change the basename of the archive, and thanks to the -p option you can
change the path at any time. But first we will list the database
-B my_base.dmd -l
It shows the following:
dar options :
archive # |
path | basename
We should change the path of archive number 1 for dar_manager looks on
the zip drive:
-B my_base.dmd -p 1 /mnt/zip
and also replace the name of the extracted catalogue by the real
-B my_base.dmd -b 1 linux_full
Now we have exactly the same database as if we had use the real archive
instead of its catalogue:
-B my_base.dmd -l
dar options :
archive # |
path | basename
In place of using -b and -p options, you can also tell the path and the
name of the real archive to use at restoration time this way when you add the catalogue to the database:
-B my_base.dmd -A ~/Catalogues/CAT_linux_full /mnt/zip/linux_full
This is done adding an optional argument. The first ~/Catalogue... is
the archive where to read the catalogue from, and the second /mnt/zip... is the name to keep for
it. No access is done to this second archive at the time of the addition, thus it may stay unavailable at
the time the command is typed.
You can add up to 65534 archives to a given database, and have as much
base as you want.
Note that we did not yet gave important options in the database to be
passed to dar. For example, you will likely restore from the root of
your filesystem, therefor dar when called from dar_manager must get the
"-R /" option. This is done with:
-B my_base.dmd -o -R /
All that follows -o is passed to dar as-is. You can see the options
passed to dar when listing the database contents (-l option).
Let's suppose that after each backup you took the time to update your database,
and now you just have removed an important file by error.
Now, we can restore our /home/denis/my/precious/file :
-B my_base.dmd -r home/denis/my/precious/file
dar_manager will find the proper archive to use, and call dar with the
<archive> -R / home/denis/my/precious/file
in turn will ask you the corresponding slices. If you want to restore
more files at a time or even a directory tree, you can add several
arguments after -r option of dar_manager:
-B my_base.dmd -r home/denis/my/precious/file etc/fstab home/joe
Once an archive become obsolete you can delete it from the database
thanks to the -D option, you can also change archive order (-m option),
get a list in which is located a given file (-f option), get the list
of most recent files in a given archive (-u option), and get overall
statistics per archive (-s option). Lastly you can specify which dar
command to use given its path (-d option), by default, dar_manager uses
the PATH shell variable to choose the dar command.
A new feature for those that are really very lazy: dar_manager has
an interactive mode, so you don't have to remeber all these
command-line switch except one:
dar_manager -B my_base.dmd
Interactive mode allow you to do all operation except restoration which
can be done as previously explained.
TO GO FURTHER WITH DAR/LIBDAR
Well, we have reached the end of this tutorial, but dar/libdar has still a lot of features to be discovered:
- strong encryption
- archive merging
- decremental backup
- dar command-line files (DCF)
- user commands between slices (and DUC files)
- Extended Attribute manipulations
- hard links
- Sparse files
- remote backup over ssh
- suspending/resuming a database from dar before/after backing it up
- using regex in place of glob expressions in masks
- using dar with tape thanks to the sequential reading mode
- having dar adding padded zeros to slice numbers
- excluding some files from compression
- asking dar to retry saving a file if it changes a the time of the backup
- what is a "dirty" files in a dar archive
- listing an archive contents under XML format
- using conditional syntax in DCF files
- using user targets
- adding user comments in dar archive
- using DAR_DCF_PATH and DAR_DUC_PATH environment variables
all this is described in much details in the following documents:
, command-line usage notes
, man pages
. You can find out more precisely where, using the feature description page
. However if you find some thing unclear, feel free to report or ask for help on dar-support mailing-list
Well, English is not my mother tong and I have not the pretention to
perfectly speak or write it, while I do my best to produce something
correctly written. Thus, if you find some weird english sentences,
spelling or typo errors, feel free to send me your feedback. You can
use dar-support mailing-list or contact me directly (read the AUTHOR
file from the dar source package to find out how to contact me).