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# TUTORIAL

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## Introduction

This little tutorial shows you how to backup your file system (partially or totally) on ZIP drives.

### 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 example. IMPORTANT: 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 the binary (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 dll.
(You could also add man pages, 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 man pages are 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: 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 full
*** 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
-z uses gzip compression algorithm, but you could also use -y to use bzip2 compression. 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)
There are some files you 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 do not apply to directories, nor to path, they just apply to
filenames. (see also -I option 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 . Theses 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
Note that path must be relative to -R option (thus no leading '/' must be used) Unlike the -X/-I options, the -P can apply to a directory. If a directory matches -P option, all its subdirectory will also be excluded. note also that -P can receive wilder cards, and they must be quoted not to be interpreted by the shell: -P "home/*/.mozilla/cache" 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): -P home/joe/.bashrc for example would only exclude joe's .bashrc file not any other file, while -X .bashrc will exclude any file of that name including joe's file. (see also -g option in man page for more)
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 should also have excluded all files of extension "dar" which are backup generated by dar with -X "*.*.dar", but this would exclude other dar archive from the backup, which may not always fit your need.
Now, as we don't save the /dev/pts /proc and /mnt/zip directories, we would have to create them by hand at recovery time. But we can better use the -D option, which does not totally ignore excluded directories but rather stores 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" as it is supposed to take place on the ZIP drive, its path is /mnt/zip/linux_full
*** 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 /etc/fstab file.
`mount /mnt/zip`
Copy the dar binary to the zip drive (to be able to restore in case of big problem, like a crash disk) and eventually man pages
`cp `which dar_static` /mnt/zip`
then, type the following
`cd /`
`dar -c /mnt/zip/linux_full -s 100M -S 95M -p -b -z -R / -X "*~" -X ".*~" -P dev/pts -P proc -P mnt/zip -D`
``
Note 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 and display a message. You will have to unmount the floppy
``
``
`umount /mnt/zip
`
eject and replace the floppy by an empty new one and mount it
`mount /mnt/zip`
To be able to to that, you can swap to another virtual console pressing ALT+F? keys, or open another xterm if under X-Windows, and suspend dar by typing CTRL-Z and reactivating it after mounting/unmounting by typing `fg` (without the quotes).
Then proceed with dar, 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 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 have 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
to run:
`dar -l /mnt/zip/linux_full`
Optionally if you don't trust your zip floppies, you can either check the archive contents, or compare what's stored in it with the current file system.
`dar -t /mnt/zip/linux_full`
will check the whole archive.
It is recommended to first unmount it and remount it, this to flush the cache. Else you may read data from cache (in memory) and do not detect an error on you floppy. 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 like:
`diff /mnt/cdrom/linux_full.132.dar /tmp/linux_full.132.dar`
where 132 has to be replaced by the real slice number.
If all is ok (which is when diff does not complain), you can delete the slice from the hard disk (/tmp/slice.x.dar), and continue with dar. Else, you will have to burn again the slice on a new CD-R.
`dar -d /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 backup, let's call it linux_diff1
*** 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 it. 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 option.
All together we get:
`dar -c /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 -D`
the same way we have done previously, just before effectively starting to backup, dar will ask for the first and then the last slice of the archive of reference, then dar will pause for you to change the floppy and put the one you want to put the backup on (thanks to the -p option).

### STEP 3: ENDLESS DIFFERENTIAL BACKUP

You can make another differential backup, taking linux_diff1 as reference, in this case you would change only the following
`-c /mnt/zip/linux_diff2 -A /mnt/zip/linux_diff1`
You could also decide to change of device, taking a 1'44MB floppy or a CD-R, this would not cause any problem at all. It arrives a time when you get many differential backup for a single full backup, it is then time to make a new full backup, 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 man page for more.
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 they are the same, all depends on the nature of the reference backup you take.
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).

### STEP 4: RECOVER AFTER A DISK CRASH

Sorry, it arrived, your old disk has crashed. OK, you are happy because you have now a good argument to buy the very fast and very enormous very last hard disk available. Usually, you also cry because you have lost data and you will have to reinstall all your system, that was working for so long!
If 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 (if necessary). You will need a bootable floppy, with a minimum Linux system on it, that allows you to access your zip drive and your new empty hard disk (in the case your backup resided on ZIP disk). For example use the Slackware floppy disks, they are nicely done. You don't need to install something on your brand-new disk, just make partitions and format as you want: We suppose your new disk is /dev/hda and /dev/sga is your ZIP drive.
1. Create the partition table as you wish, using
`fdisk /dev/hda`
2. Format the ext2 partition which will receive your data
`mke2fs /dev/hda1`
3. Additionally format the swap partition (if needed)
`mkswap -c /dev/hda2`
3bis. If you have a lot of file to restore, you can activate the swap on the partition of your new hard drive:
`swapon /dev/hda2`
4. Now we must mount the hard disk, somewhere.
`cd /`
`mkdir disk`
`mount -t ext2 /dev/hda1 /disk
`
would do the trick
4bis. If you want to restore your system over several partitions like /usr /var /home and / you must create the partitions, format them. Then create the directories that will be used as mounting point an mount the partitions on theses directories
`mkdir /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
`
for example if you have / /usr /var and /home partitions.
5. We need to copy the dar binary from the ZIP to your disk insert the floppy ZIP where you have copied the dar binary
`
cd /`
`mkdir zip`
`mount -t ext2 /dev/sga /zip`
`cp /zip/dar_static /disk
`
where /dev/sga points to your zip drive
6. Now we restore the archive. The stuff has to go in /disk subdirectory
*** here comes the option: -R /disk
7. 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
let's go restoring!
`/disk/dar_static -x /zip/linux_full -R /disk -b`
... and when the next zip floppy is needed,
`umount /zip`
change the floppy and mount it:
`mount -t ext2 /dev/sga /zip`
as previously, use an alter xterm / virtual console or suspend dar by CTRL-Z and awake it back by the 'fg' command. Then press <enter> to proceed with dar
7. Once finished with the restoration of linux_full, we have to do the same with any following backup, This way however will warn you any time it 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, but you may also use the -r option, that will avoid trying to overwrite more recent files than those on filesystem. It might not be of a great use, if you restore a differential backup after its reference backup on an initially empty disk (file stored in the differential archive are more recent than those in the reference). But, it might be useful in some other situations.
All together it makes:
`/disk/dar_static -x /zip/linux_diff1 -R /disk -b -w`
Then any additional archive:
`/disk/dar_static -x /zip/linux_diff2 -R /disk -b -w
...
/disk/dar_static -x /zip/linux... -R /disk -b -w`
8. Finally, remove the dar binary from the disk:
`rm /disk/dar_static`
9. And launch lilo for your Linux box to boot properly (if needed):
`lilo -r /disk`
10. You can reboot you machine and be happy with you brand-new hard disk with your old precious data on it:
`shutdown -r now`
OK, one day, I will make something like a bootable floppy image with dar inside, maybe with a simple script for user interaction... if you have already done it, you can tell or send me (or give me the URL where to get it, for I add a hyperlink on DAR's Homepage). [Note: Knoppix seems to include dar]

### STEP 4(bis): recover only some files

Gosh, you have remove a important 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 archive:
``
``
`dar -R / -x /zip/linux_full -g home/denis/my_precious_file`
This would restore only the file /home/denis/my_precious_file from the full backup.
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 backup.
`dar -R / -x /zip/linux_diff1 -g home/denis/my_precious_file`
and so on, up to the last differential archive.
`dar -R / -x /zip/linux_diff29 -g home/denis/my_precious_file`

#### b) Second method (more efficient):

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 each 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 option (verbose):
`dar -R / -x /zip/linux_diff29 -v -g home/denis/my_precious_file`
If we can see a line like
`restoring file: /home/denis/my_precious_file`
The it stops here, because we got the most recent backup version of our lost file. We have to otherwise have to continue with the previous differential backup, up to the full backup if it is necessary. This method has an advantage over 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 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:
``
``
`dar -x /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 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 where restoring more than one file using the second method. Instead, in the first method (restoring first from the full backup, then from all the following differential backups), -r option is not so important as 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 lots here to automate the restoration of a set of file.
How much can you restore with dar_manager? As much as you can give to dar_manager as argument on command line or through included files (-B option).

### DAR_MANAGER TUTORIAL

dar_manager builds a database of all your archive contents, to automatically restore the latest versions of a given set of files. First, we have to create a "database" file :
`dar_manager -C my_base.dmd`
This created a file "my_base.dmd" where dmd stands for Dar Manager Database, but you are free to use any other filename.
This database is created empty. Each time you make a backup, may it be full or differential, you will have to add its catalogue to this database using the following command:
`dar_manager -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!
`dar_manager -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 contents:
`dar_manager -B my_base.dmd -l`
It shows the following:
`dar path :
dar options :
archive # | path | basename
------------+--------------+---------------
1 /home/denis/Catalogues CAT_linux_full
`
We should change the path of archive number 1 for dar_manager looks on the zip drive:
`dar_manager -B my_base.dmd -p 1 /mnt/zip`
and also replace the name of the extracted catalogue by the real archive name
`dar_manager -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:
`dar_manager -B my_base.dmd -l`
`dar path :
dar options :
archive # | path | basename
------------+--------------+---------------
1 /mnt/zip linux_full
`
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:
`dar_manager -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 to add, and the second /mnt/zip... is the name to keep for it. No access is done to this archive, thus it may be not available 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.
Suppose after each backup you took the time to update your database, and now you just have removed an important file by error.
Firstly, 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:
`dar_manager -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).
Now, we can restore our /home/denis/my/precious/file :
`dar_manager -B my_base.dmd -r home/denis/my/precious/file`
dar_manager will find the proper archive to use, and call dar with the following options:
`dar -x <archive> -R / home/denis/my/precious/file`
Which in turn will ask you the corresponding slices.
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.
An a new feature for those that are really very lazy : dar_manager has an interactive mode, so you don't have to remeber all theses command-line switch except one:
`
`
`dar_manager -B my_base.dmd -i`
Interactive mode allow you to do all operation except restoration which can be done as previously explained.