Backing Up to CD (Or DVD) with cdbackup 383

Backing Up to CD (Or DVD) with cdbackup

Without a little help, tar cannot write archives directly to CD or DVD media. You could write an archive to your hard drive and then copy the archive to a CD (or DVD) with a tool like k3b or nautilus, but that’s a hassle. You’d need enough free space on your hard drive to hold the intermediate copy, and you’d have to figure out how to split a big archive onto multiple discs — definitely not a timesaving technique.

Fortunately, the open-source community comes to the rescue again. The cdbackup and cdrestore commands are helper programs that you can use with tar to write archives onto a CD or DVD. cdbackup writes straight onto a CD or DVD without laying down a file system first. That saves you some space and time, but you won’t be able to read the discs with other programs. cdbackup can write a large archive to multiple discs (something that tar can’t do by itself). Because cdbackup cooperates so well with tar, you can use the combination to create complete backups, incremental backups, and differential backups that span multiple discs.

You can find the CDBackup package at the author’s Web site: www.muempf.de/index.html.

Creating the backup

Creating a multidisc backup with tar and cdbackup is easy:

1. Type in the tar command that archives the data that you want to save and then tell tar to write the archive to its standard output stream, like this (but don’t press Enter yet):

# tar -zcvf - /home /etc

2. Then pipe the archive to cdbackup:

#tar -zcvf - /home /etc | cdbackup -m -r 0,0,0 -a “My Backup”

If you’re burning a DVD instead of a CD, be sure to include -l 4600 in your command line so cdbackup knows that it can write up 4.6GB per disc (-l 4700 might be safe too, but leave yourself a little wiggle room).

tar starts building the archive, and when it has enough data, cdbackup starts writing it to CD (or DVD).

3. Press Enter, and your backup begins.

4. When cdbackup fills the first disc, it prompts you to insert a new one. After you do so, press Enter to continue.

Under the hood, cdbackup uses the cdrecord package to do the tough work. In fact, you can pass command line options to the underlying cdrecord command when you invoke cdbackup. Table 50-1 lists some of the more useful cdbackup options.

TABLE 50-1: HANDY CDBACKUP OPTIONS

Option	What It Does
-m	Enables multidisc recording
-r device	Specifies which CD/DVD drive to record to
-s speed	Specifies the write speed (the default write
	speed is 4, or 4 times the normal write
	speed)
-a label	Adds a descriptive name (label) to the
	archive set
-l size	Tells cdbackup how many megabytes can
	fit on one disc (the default is 650 — about
	the size of a blank CD)
-- options	Passes command line options to the
	cdrecord command

384 Technique 50: Backing Up Your Data

“No, I don’t want a moment to reflect on my backup.”

By default, cdrecord (and therefore cdbackup) pauses for ten seconds before it starts burning a CD, giving you a chance to change your mind and cancel the burn. That pause can get a bit annoying after a while. You can shorten the delay by including a cdrecord option at the end of the command line:

#tar -zcvf - /home /etc | cdbackup -m -r 0,0,0 -a “My Backup” -- gracetime=2

The -- flags tells cdbackup to pass the rest of the command line options to cdrecord. In this case, gracetime=2 shortens the preburn delay to 2 seconds (the minimum allowed by cdrecord).

If you don’t know the full name of your CD/DVD recorder, run the following command:

# cdrecord -scanbus

You should see a result similar to this:

scsibus1:

1,0,0 100) ‘TEAC’ ‘DW-224E ‘ ‘F.0A’ CDRW

1,1,0 101) *

1,2,0 102) *

1,3,0 103) *

1,4,0 104) *

1,5,0 105) *

1,6,0 106) *

1,7,0 107) *

Find your recorder in the list: The first three numbers on that line make up the device number. If you see more than one device in the list, choose your drive by its model name. In our case, we would tell cdbackup to record on device

1,0,0.

Restoring from a CD or DVD backup

To restore a file (or set of files), you use cdrestore and tar. For example, to restore the /etc/passwd file from a backup set, place the first disc in the drive and then type this command:

#cdrestore /dev/cdrom -t 1 | \ tar -zxvf - /etc/passwd

If the file you’re looking for is not on the first disc, cdrestore prompts you to insert the next disc; press Enter to continue. In fact, cdrestore asks you to insert the next disc even if it does find /etc/passwd on the first disc. cdrestore can’t tell when tar has finished its work, so when you’re sure you have the files that you need, you can just press Ctrl-C to kill the job. Be careful though, because the file that you’re looking for may be split across multiple discs.

When you run cdrestore, you can use the normal /dev/cdrom device name instead of -r 1,0,0. The

-t 1 option tells cdrestore to read from the first track on the disc (yes, cdbackup can write multiple tracks so cdrestore can read them). Pipe the output from cdrestore to tar and tell tar to extract the files that you want. Notice that you can use compression (either the -z gzip variety or the -j bzip2 variety). You have to specify the compression type when you create the archive and when you restore from the archive.

To see a listing of the archive content, use the following command:

# cdrestore /dev/cdrom -t 1 | tar -ztvf -

The cdrestore part of the command is the same, but you use the -t flag to list the content instead of -x to extract it. You can also use the -q flag to view information about the disc that you have in the drive:

# cdrestore -q /dev/cdrom Tracks: 1

Disk size: 666000 kB ( 333000 blocks) Space used: 1872 kB ( 936 blocks) Space avail: 641328 kB ( 320664 blocks) Track 01: 1 MB: Part 2: My Backup

Restoring from a disc containing multiple archives

One of nicest cdrecord features is that you can write multiple archives to the same disc. For example, if you use an incremental or differential backup plan, you might do a complete backup on Sunday and an

Backing Up to CD (Or DVD) with cdbackup 385

incremental (or differential) backup every weekday. The weekday backups are likely to be small enough to fit on a single disc without filling it up. With cdrecord, just put Monday’s disc in the drive when you create Tuesday’s archive because cdbackup is smart enough to append the new archive to the end of the disc. If you have multiple tracks on the same disc, cdrestore -q shows you all of them:

# cdrestore -q /dev/cdrom Tracks: 3

Disk size: 666000 kB ( 333000 blocks) Space used: 64442 kB ( 32221 blocks) Space avail: 587758 kB ( 293879 blocks) Track 01:10 MB: Part 1: Monday’s backup Track 02:20 MB: Part 1: Tuesday’s backup Track 03:10 MB: Part 1: Wednesday’s backup

When you restore from a multitrack disc set, just tell cdrestore which track you want to start with, as in the following example:

#cdrestore /dev/cdrom -t 2 | \ tar -zxvf - /etc/passwd

The -t 2 flag tells cdrestore to read from track 2 (Tuesday’s backup).

51 Quick Backup to Remote Storage

Technique

Save Time By

Creating and moving archives with tar and ssh

Backing up to tape drives on remote hosts

Using rdist with ssh for simple remote backups

Creating simple remote backup commands that you can automate

The price of a well-outfitted computer has dropped to the point where it’s feasible to use a second computer as a backup device. Keeping a backup computer system on your own network or at

another office accessible from the Web is a viable option for many companies. You don’t need fancy backup software to mirror your data on a remote computer; Linux already includes the tools to do the job.

In Technique 50, we show you how to use the tar program to create archives of your data. In this technique, we show you how to combine tar and ssh (the secure shell) to create archives on a remote computer. When you use ssh to back up your data, the data stream is encrypted, so you’re guaranteed that your important files won’t be read by the world. You can use ssh across your local network or across the Web with equal ease. Backing up with ssh is easier and quicker than mounting a network drive — you don’t even need superuser privileges.

Piping compressed archives created by the tar command to the ssh command makes it easy and quick to back up to remote hosts. You can create an archive containing your important files and move it to a remote host with just one command. It doesn’t get much quicker than that.

You can also use the tar command in combination with ssh to write to tape drives on remote machines. It’s a quick way to share resources on your network without a lot of hardware investment or software conflicts.

We also introduce you to the rdist command. With rdist, you can create a mirror image of your working system on a remote machine. A complete copy of your important information is not only safe, but also ready to use in an instant. Use the rdist command with ssh to make the remote connection simple, fast, and secure. By using Task Scheduler with rdist and ssh, you can even automate your nightly backups.

In this technique, we show you some shortcuts that work with some old favorites to make backing up to remote systems quick and easy.