Andrew Hudson - Fedora™ Unleashed, 2008 edition

Choosing New from the File menu creates new archives. You then type the name of the archive, providing the appropriate extension (. tar, . gz, and so on), and then proceed to add files and directories as you desire.

Provided with Fedora, Amanda is a powerful network backup application created by the University of Maryland at College Park. Amanda is a robust backup and restore application best suited to unattended backups with an autoloading tape drive of adequate capacity. It benefits from good user support and documentation.

Amanda's features include compression and encryption. It is intended for use with high-capacity tape drives, optical, CD-R, and CD-RW devices.

Amanda uses GNU tarand dump; it is intended for unattended, automated tape backups, and is not well suited for interactive or ad hoc backups. The support for tape devices in Amanda is robust, and file restoration is relatively simple. Although Amanda does not support older Macintosh clients, it uses Samba to back up Microsoft Windows clients, as well as any Unix client that can use GNU tools (which includes Mac OS X). Because Amanda runs on top of standard GNU tools, you can restore files using those tools on a recovery disk even if the Amanda server is not available. File compression can be done on either the client or server, thus lightening the computational load on less powerful machines that need backing up.

Amanda does not support dumpimages larger than a single tape and requires a new tape for each run. If you forget to change a tape, Amanda continues to attempt backups until you insert a new tape, but those backups will not capture the data as you intended them to. Do not use too small a tape or forget to change a tape, or you will not be happy with the results.

There is no GUI interface for Amanda. Configuration is done in the time-honored Unix tradition of editing text configuration files located in /etc/amanda. The default installation in Fedora includes a sample cronfile because it is expected that you will be using cronto run Amanda regularly. The client utilities are installed with the package am-utils; the Amanda server must be obtained from the Amanda website. As far as backup schemes are concerned, Amanda calculates an optimal scheme on the fly and schedules it accordingly. It can be forced to adhere to a traditional scheme, but other tools are possibly better suited for that job.

The man page for Amanda (the client is amdump) is well written and useful, explaining the configuration of Amanda as well as detailing the programs that actually make up Amanda. The configuration files found in /etc/amandaare well commented; they provide a number of examples to assist you in configuration.

The program's home page is http://www.amanda.org/. There, you will find information on subscribing to the mail list, as well as links to Amanda-related projects and a FAQ.

The free download version of Fedora does not provide any other sophisticated backup applications, but Red Enterprise Linux has a variety of third-party software available. Commercial and other freeware backup products do exist; BRU and Veritas are good examples of effective commercial backup products. Here are some useful free software backup tools that are not installed with Fedora:

► flexbackup— This backup tool is a large file of Perl scripts that makes dumpand restoreeasier to use. You can access flexbackup's command syntax by using the command with the -helpargument. You also can use afio, cpio, and tarto create and restore archives locally, or over a network by using rshor sshif security is a concern. Its home page is http://www.flexbackup.org/.

► afio— This tool creates cpio-formattedarchives, but handles input data corruption better than cpio(which does not handle data input corruption very well at all).

It supports multivolume archives during interactive operation and can make compressed archives. If you feel the need to use cpio, you might want to check out afioathttp://freshmeat.net/projects/afio/.

► cdbackup— Designed for the home or small office user, cdbackupworks with any backup and restores software that can read from stdin, write to stdout, and can handle linear devices such as tape drives. It makes it easier to use CD-Rs as the storage medium. Similar applications are available elsewhere as well; the home page for this application is at http://www.muempf.de/index.html.

Many other alternative backup tools exist, but covering all of them is beyond the scope of this book. Two good places to look for free backup software are Freshmeat (http://www.freshmeat.net/) and Google (http://www.google.com/linux).

Often, when you have only a few files that you need to protect from loss or corruption, it might make better sense to simply copy the individual files to another storage medium rather than to create an archive of them. You can use the tar, cp, rsync, or even the cpiocommands to do this, as well as a handy file management tool known as mc.Using taris the traditional choice because older versions of cpdid not handle symbolic links and permissions well at times, causing those attributes (characteristics of the file) to be lost; tar handled those file attributes in a better manner. cphas been improved to fix those problems, but taris still more widely used.

To illustrate how to use file copying as a backup technique, the examples here show how to copy (not archive) a directory tree. This tree includes symbolic links and files that have special file permissions that must be kept intact.

One choice for copying files into another location is to use the tarcommand where you would create a tarfile that would be piped to tar to be uncompressed in the new location. To accomplish this, first change to the source directory. Then, the entire command resembles

# tar cvf - files | (cd target_directory ; tar xpf -)

where files are the filenames you want to include; use *to include the entire current directory.

Here is how the command shown works: You have already changed to the source directory and executed tarwith the cvf - arguments that tell tarto

► c— Create an archive.

► v— Be Verbose; lists the files processed so we can see that it is working.

► f— Use the filename of the archive will be what follows. (In this case, it is -.)

► - — Use a buffer; a place to hold data temporarily.

The following tar commands can be useful for creating file copies for backup purposes:

► l— Stay in the local file system (so that you do not include remote volumes).

► atime-preserve— Do not change access times on files, even though you are accessing them now, to preserve the old access information for archival purposes.

The contents of the tarfile (held temporarily in the buffer, which is named -) are then piped to the second expression, which extracts the files to the target directory. In shell programming (refer to Chapter 10, "Managing Users"), enclosing an expression in parentheses causes it to operate in a subshell and be executed first.