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gzip, and a few related tools for making backups to CD and tape. We even cover the use of tape drives, as well as CD-R in the bargain. These tools allow you to make backups more or less "by hand"; you can automate the process by writing shell scripts and even schedule your backups to run automatically during the night using cron. All you have to do is flip tapes. Other software packages provide a nice menu-driven interface for creating backups, restoring specific files from backup, and so forth. Many of these packages are, in fact, nice frontends to tar and gzip. You can decide for yourself what kind of backup system suits you best.

Simple Backups

The simplest means of making a backup is to use tar to archive all the files on the system or only those files in a set of specific directories. Before you do this, however, you need to decide what files to back up. Do you need to back up every file on the system? This is rarely necessary, especially if you have your original installation disks or CD-ROM. If you have made important changes to the system, but everything else is just the way it was found on your installation media, you could get by with only archiving those files you have made changes to. Over time, however, it is difficult to keep track of such changes.

In general, you will be making changes to the system configuration files in /etc. There are other configuration files as well, and it can't hurt to archive directories such as /usr/lib and /etc/X11 (which contains the XFree86 configuration files, as we saw in "Installing X.org" in Chapter 16).

You should also back up your kernel sources (if you have upgraded or built your own kernel); these are found in /usr/src/linux.

During your Linux adventures it's a good idea to keep notes on what features of the system you've made changes to so that you can make intelligent choices when making backups . If you're truly paranoid, go ahead and back up the whole system; that can't hurt, but the cost of backup media might.

Of course, you should also back up the home directories for each user on the system; these are generally found in /home. If you have your system configured to receive electronic mail (see "The Postfix MTA" in Chapter 23), you might want to back up the incoming mail files for each user. Many people tend to keep old and "important" electronic mail in their incoming mail spool, and it's not difficult to accidentally corrupt one of these files through a mailer error or other mistake. These files are usually found in /var/spool/mail. Of course, this applies only if you are using the local mail system, not if you access mail directly via POP3 or IMAP.

Backing up to tape

Assuming you know what files or directories to back up, you're ready to roll. You can use the tar command directly, as we saw in "Using tar" in Chapter 12, to make a backup. For example, the command:

tar cvf /dev/qft0 /usr/src /etc /home

archives all the files from /usr/src, /etc, and /home to /dev/qft0. /dev/qft0 is the first "floppy-tape" device—that is, a tape drive that hangs off of the floppy controller. Many popular tape drives for the PC use this interface. If you have a SCSI tape drive, the device names are /dev/st0, /dev/st1, and so on, based on the drive number. Those tape drives with another type of interface have their own device names; you can determine these by looking at the documentation for the device driver in the kernel.

You can then read the archive back from the tape using a command such as:

tar xvf /dev/qft0

This is exactly as if you were dealing with a tar file on disk, as discussed in "Archive and Compression Utilities" in Chapter 12.

When you use the tape drive, the tape is seen as a stream that may be read from or written to in one direction only. Once tar is done, the tape device will be closed, and the tape will rewind. You don't create a filesystem on a tape, nor do you mount it or attempt to access the data on it as files. You simply treat the tape device itself as a single "file" from which to create or extract archives.

Be sure your