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rdup-backups - introduction into making backups with rdup

rdup is a simple program that prints out a list of files and directories that are changed changed on a filesystem. It is more sophisticated than for instance find, because rdup will find files that are removed or directories that are renamed.

A long time ago rdup included a bunch of shell and Perl scripts that implemented a backup policy. These could be used in a pipeline to perform a backup.

Currently rdup consists out of three basic utilities:

With rdup you create the file list on which later programs in the pipeline can work. The default output format also includes the files' content. rdup can be seen as a tar replacement in this respect, but rdup also allows for all kinds of transformations of the content (encryption, compression, reversal), see the -P switch in rdup(1) for more information.

With rdup-tr you can transform the files rdup delivers to you. You can create tar, cpio or pax files. You can encrypt pathnames. rdup-tr is filter that reads from standard input and writes to standard output. See rdup-tr(1) for more information. With rdup and rdup-tr you can create an encrypted archive which is put in a directory structure that is also encrypted.

With rdup-up you can update an existing directory structure with the updates as described by rdup.

rdup-up reads rdup input and will create the files, symbolic links, hard links and directories (and sockets, pipes and devices) in the file system. See rdup-up(1) for more information.

So the general backup pipeline for rdup will look something like this:

create filelist | transform | update filesystem ( rdup | rdup-tr | rdup-up )

Note 1:
The same sequence is used for restoring. In both cases you want to move files from location A to B. The only difference is that the transformation is reversed when you restore.

Note 2:
The use of rdup-tr is optional.

For rdup there is no difference between backups and restores. If you think about this for a minute you understand why.

Making a backup means copying a list of files somewhere else. Restoring files is copying a list of files back to the place they came from. Same difference. So rdup can be used for both, if you did any transformation with rdup during the backup you just need to reverse those operations during the restore.

It is always best to backup to another medium, be it a different local harddisk or a NFS/CIFS mounted filesystem. You can also use ssh to store file on a remote server, ala rsync (although not as network efficient).

If you backup to a local disk you can just as well use rsync or plain old tar, but if you store your files at somebody else's disk you will need encryption. This is where you go beyond rsync and rdup comes in. Rsync cannot do per-file encryption, sure you can encrypt the network traffic with ssh, but at the remote side your files are kept in plain view. If you implement remote backups, the easy route is to allow root access on the backup medium. If the backup runs without root access the created files will not have their original ownership. For NFS this can be achieved by using no_root_squash, for ssh you could enable PermitRootLogin. Note that this may be a security risk.

We need a little help here in the form of the rdup-simple script. Keep in mind that the following scripts can also be run remotely with the help of ssh.

The following script implements the algorithm of rdup-simple.

# some tmp files are saved in ~/.rdup. This directory must exist
DIR=/home	    # what to backup
TODAY=$(date +%Y%m/%d)
# for remote backup, this has to run on the remote host!
case $RET in
	echo Error >&2
	exit 1
	# full dump, remove file-list and time-stamp file
	# inc dump
	# do nothing here
# this is the place where you want to modify the command line
# right now, nothing is translated we just use 'cat'
rdup -N $STAMP -Pcat $LIST $DIR | rdup-up $BACKUP/$HOSTNAME/$TODAY
# or do a remote backup
#rdup -N $STAMP -Pcat $LIST $DIR | ssh root@remotehost \

With rdup-simple you can easily create backups. Backing up my home directory to a backup directory:

rdup-simple ~ /vol/backup/$HOSTNAME

This will create a backup in /vol/backup/$HOSTNAME/200705/15. So each day will have its own directory. Multiple sources are allowed, so:

rdup-simple ~ /etc/ /var/lib /vol/backup/$HOSTNAME

Will backup your home directory, /etc and /var/lib to the backup location. Also if you need to compress your backup, simple add a '-z' switch:

rdup-simple -z ~ /etc/ /var/lib /vol/backup/$HOSTNAME

For a remote backup to work, both the sending machine and the receiving machine must have rdup installed. The currently implemented protocol is ssh.

Dumping my homedir to the remote server:

rdup-simple ~ ssh://miekg@remote/vol/backup/$HOSTNAME

The syntax is almost identical, only the destination starts with the magic string 'ssh://'. Compression and encryption are just as easily enabled as with a local backup, just add '-z' and/or a '-k keyfile' argument:

rdup-simple -z -k 'secret-file' ~ ssh://miekg@remote/vol/backup/$HOSTNAME

Remember though, that because of these advanced features (compression, encryption, etc, ...) the network transfer can never be as efficient as rsync.

rdup(1), rdup-tr(1), rdup-up(1) and
15 Dec 2008 1.1.x

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