Fedora™ Unleashed, 2008 edition

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 dump and restore easier to use. You can access flexbackup's command syntax by using the command with the -help argument. You also can use afio, cpio, and tar to create and restore archives locally, or over a network by using rsh or ssh if security is a concern. Its home page is http://www.flexbackup.org/.

> afio — This tool creates cpio-formatted archives, 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 afio athttp://freshmeat.net/projects/afio/.

> cdbackup — Designed for the home or small office user, cdbackup works 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).

Copying Files

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 cpio commands to do this, as well as a handy file management tool known as mc. Using tar is the traditional choice because older versions of cp did 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. cp has been improved to fix those problems, but tar is 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.

Copying Files Using tar

One choice for copying files into another location is to use the tar command where you would create a tar file 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 tar with the cvf - arguments that tell tar to

> 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 tar file (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.

First we change to the target directory, and then

> x — Extract files from a tar archive.

> p — Preserve permissions.

> f — Read from -, the temporary buffer that holds the tar'ed files.

Compressing, Encrypting, and Sending tar Streams

The file copy techniques using the tar command in the previous section can also be used to quickly and securely copy a directory structure across a LAN or the Internet (using the ssh command). One way to make use of these techniques is to use the following command line to first compress the contents of a designated directory, and then decompress the compressed and encrypted archive stream into a designated directory on a remote host:

$ tar cvzf - data_folder | ssh remote_host '( cd ~/mybackup_dir; tar xvzf - )'

The tar command is used to create, list, and compress the files in the directory named data_folder. The output is piped through the ssh (secure shell) command and sent to the remote computer named remote_host. On the remote computer, the stream is then extracted and saved in the directory named /mybackup_dir. You are prompted for a pass word to send the stream.

Copying Files Using cp

To copy files, we could use the cp command. The general format of the command when used for simple copying is the following:

$ cp -a source_directory target_directory

The -a argument is the same as giving -dpR, which would be