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<!-- ISBN=0672311623 //-->

<!-- TITLE=SAMS TEACH YOURSELF LINUX IN 24 HOURS //-->

<!-- AUTHOR=BILL BALL, STEPHEN SMOOGEN //-->

<!-- PUBLISHER=MACMILLAN //-->

<!-- IMPRINT=SAMS //-->

<!-- PUBLICATION DATE=1998 //-->

<!-- CHAPTER=23 //-->

<!-- PAGES=0339-0346 //-->

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<P><CENTER>

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<A NAME="PAGENUM-339"><P>Page 339</P></A>













<H3><A NAME="ch23_ 2">

Hour 23

</A></H3>







<H2>

<A NAME="ch23_ 3">

Archiving

</A>

</H2>



<P>This hour continues the discussion of basic system administration skills and shows you

how to back up and restore your system by using several different Linux utilities (included

on your CD-ROM). With a little effort, you'll be able to easily perform these

system administration tasks.

</P>



<H3><A NAME="ch23_ 4">

Considerations Before Performing Backups and Restores

</A></H3>



<P>There are several things you should consider before backing up or restoring your

system. Although one ideal time to back up is after you've installed Linux and made sure all

your devices (such as the sound card, graphics card, or tape drive) are working, there are

other considerations. For example, if the kernel supplied on the CD-ROM works well for

your system, then you can simply rely on the CD for your initial backup in case you have to

do a full restore.

</P>



<P>You should understand the difference between a backup and an archive. Backups

are performed at regular intervals to save important documents, files, or complete

systems.

</P>

<A NAME="PAGENUM-340"><P>Page 340</P></A>





<P>

Archives are made to save important documents, files, or complete systems for long

periods of time. This means that you should first devise a backup strategy and ask yourself

the following questions:

</P>

<UL>

<LI>          Do I need to use a formal backup strategy?

<LI>          Do I need to back up the entire system each time?

<LI>          Do I need to back up selected files or whole directories?

<LI>          How often should I do the backup?

<LI>          How long do I need to keep my archived copies?

<LI>          Do I need reports or statistics on the backups?

<LI>          What media (such as floppy or tape) should I use?

<LI>          What software format (such as tar or dump) should the backup be in?

<LI>          Do I need to use any specialized software tools, such as backup scripts, or can

I perform the backups by hand?

<LI>          Should compression, straight copying, or encryption be used?

</UL>



<P>You can answer some of these questions by looking at the way you use your Linux

system. If you're just using Linux for word processing or running spreadsheets, you can

probably get away with only backing up certain files or directories. If you're using Linux to

learn programming, you'll want to keep not only original copies of your programs, but

perhaps different versions. If you have other users on the system, you'll want to not only save

copies of their directories, but  the /etc/passwd file, or even the whole system, so that you can

quickly restore the system  in the event of a hard drive crash (unlikely) or system operator

error (more likely).

</P>



<P>The size of your system and the capacity of your hard drives or other storage devices

may determine how to approach a backup strategy. If your Linux system is small enough

(around 200MB), you can quickly back up everything to another hard drive or to a tape drive.

You also can use a removable media drive, such as an Iomega Zip drive or Sysquest

EZ-flyer. If you only have to save copies of a small number of small files, you may even be able

to use high-density floppies for storage.

</P>



<P>You'll probably decide on a combination of archiving and regularly scheduled full

or incremental backups. You need to choose the software to use and explore how to

automate as much of the process as possible, perhaps by using

crontab entries (discussed in Hour 24, &quot;Scheduling&quot;). Whatever you do, when you decide on your strategy, stick to it! The

worst time to create and use a backup strategy is after you run into problems or lose files.

</P>

<A NAME="PAGENUM-341"><P>Page 341</P></A>







<H4><A NAME="ch23_ 5">

Backing Up Your System with the tar Command

</A></H4>



<P>Although use of the tar command was discussed in Hour 5, &quot;Manipulation and

Searching Commands,&quot; as the system administrator, you'll want to explore some of the more

complex tar command-line options and experiment with creating backups before implementing

your backup strategy.

</P>



<P>The tar command creates a tape archive. You can write the archive to your hard drive,

a tape drive, or nearly any other Linux device. To create a quick backup of your users'

home directories, use tar to create the archive. For example,

</P>



<!-- CODE SNIP //-->

<PRE>

# tar cPfC users.tar / home

</PRE>

<!-- END CODE SNIP //-->



<P>This command line creates the tape archive

users.tar in the current directory. One easy way to regularly back up these directories is to save them on a different file system. If you

have a DOS or Windows partition mounted (see Hour 21, &quot;Handling Files&quot;), automate

the backup process with a crontab entry:

</P>



<!-- CODE SNIP //-->

<PRE>

30 17 * * * root tar cPfC /mnt/dos/windows/desktop/users.tar / home

</PRE>

<!-- END CODE SNIP //-->



<P>This entry, in the /etc/crontab file, backs up your users' directories at 5:30 p.m. each day

and saves the archive in the Windows desktop folder. As you can see, automating the

backup process isn't that hard, and has the benefit of working in the background without

your attention; a process called an unattended backup. If you save your data on a separate

file system, you can easily restore the files later by using the

tar command's x, or extract, option:

</P>



<!-- CODE SNIP //-->

<PRE>

# cd /

# tar xvf /mnt/dos/windows/desktop/users.tar

</PRE>

<!-- END CODE SNIP //-->



<P>These command lines restore your users' directories and files, starting at the

/ or root directory. While backing up files to another file on your hard drive is easy, you also

can use the tar command with tape drives by specifying the tape device on the

tar command line.

</P>



<TABLE BGCOLOR=#FFFF99><TR><TD>JUST A MINUTE</TD></TR><TR><TD>

<BLOCKQUOTE>

Unfortunately, there are no utilities to format tapes under Linux. Although

you must still use a DOS or Windows utility to do this, you won't have to

bother with formatting if you make sure to purchase preformatted tapes.

</BLOCKQUOTE>

</TD></TR></TABLE>



<P>This hour doesn't detail all the ins and outs of installing or using different tape devices,

but it does show you the general approach and some examples you may want to try. To use

a tape drive with the tar command, you must find the tape device under the

/dev directory. There are a number of them, but this section uses the general floppy tape driver,

/dev/ftape, as an example.

</P>



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