Backing Up and Restoring

Backing Up and Restoring Objectives Upon completion of this module, you should be able to: • Use the tar and compress commands to back up files and directories • Use the jar command to s

Backing Up and Restoring

Objectives

Upon completion of this module, you should be able to:

• Use the tar and compress commands to back up files and directories

• Use the jar command to save and compress files and directories

• Position a tape to a selected data set using the mt utility

Discussion – How frequently do you back up or restore files?

Contents Overview

In order to back up or easily transfer files via ftp or another method, you need to be able to package and restore the files easily This module covers the following commands:

• compress

In addition, specific instructions for backing up and restoring your home directory using tar

and compress are included

The tar Command

The tar (tape archive) command enables you to back up single or multiple files in a directory hierarchy

Command Format

tar function_[letter/modifier] [output file]

filename(s)/directory(s)

Function Letters

c Create a new tar file

t List the table of contents of the tar file

x Extract the specified files from the tar file

Function Modifiers

f Specify the tar file ( /tmp/file.tar) or tape

drive (/dev/rmt/x) if other than default

v Execute in verbose mode

Saving a Directory to Tape

You can create the tar file using a relative path name

$ cd /home

$ tar cv user1

This archives the user1 directory to the default device,/dev/rmt/0

This command is also useful for creating archive files to share with other users or attach

to mail messages

$ cd

$ tar cvf files.tar file1 file2 file3

file1

file2

file3

$

You can view the table of contents of the tar file using tf or tvf option:

$ tar tf files.tar

file1

file2

file3

$

$ tar tvf files.tar

-rw-rw-r vominh/vominh 10240 2002-09-16 04:10:21 file1

rw-r vominh/vominh 12345 2002-09-16 04:10:21 file2 -rw-rw-r vominh/vominh 10240 2002-09-16 04:10:34 file3

Use tar command to extract files from an archive:

$ tar xf files.tar

Note – The existed files will be overwritten without a notice.

The compress Command

The compress command is used to compress files using a special format to reduce the size of the file from 20 percent to 80 percent

Command Format

compress filename

Compressing a File

The following example uses the -v (verbose) option to compress a file called

bin.file:

The file is compressed and a Z suffix is appended to the file name

$ compress -v bin.file

bin.file: Compression: 70.84% replaced with

bin.file.Z

Files are uncompressed using the uncompress command

Command Format: Uncompressing

uncompress filename

Uncompressing a File

$ uncompress bin.file.Z

The jar Command

The jar command is similar to the tar command, but compresses the resulting file in the same step It is a Java™ application that combines multiple files into a single JAR (Java archive) file It is also a generalpurpose archiving and compression tool, based on ZIP and the ZLIB compression format The jar command was originally created for Java programmers to download multiple files with one request, rather than having to issue a download request for each separate file jar is standard with the Linux operating system, but is available on any system that has Java virtual machine (JVM) installed

Command Format

The syntax for the jar tool is almost identical to the syntax for the tar

command

jar options [ output file ] filename(s)/directory(s)

Options

c Create a new jar file

t List the table of contents of the jar file

x Extract the specified files from the jar file

f Specify the jar file ( /tmp/file.jar) or tape drive (/dev/rmt/x) if other

than default

v Execute in verbose mode

Note – It is not necessary to use a hyphen (-) before options when

issuing the jar command

Adding All the Files in a Directory to an Archive

$ ls

dante dir1 dir3 file1 file3 fruit

dante_1 dir2 dir4 file2 file4 fruit2

$ jar cvf bundle.jar *

adding: dante (in=1320) (out=744) (deflated 43%)

adding: dante_1 (in=368) (out=242) (deflated 34%)

adding: dir1/ (in=0) (out=0) (stored 0%)

adding: dir1/coffees/ (in=0) (out=0) (stored 0%)

adding: dir1/coffees/beans (in=0) (out=0) (stored 0%)

adding: dir1/coffees/nuts (in=0) (out=0) (stored 0%)

adding: dir1/fruit/ (in=0) (out=0) (stored 0%)

adding: dir1/trees/ (in=0) (out=0) (stored 0%)

adding: dir2/ (in=0) (out=0) (stored 0%)

<output omitted>

adding: file1 (in=1696) (out=874) (deflated 48%)

<output omitted>

Note – The jar tool is not intended for backing up symbolic links

Error messages will display if this is attempted

The mt Command

The mt command enables direct tape manipulation

Command Format

mt [ -f tape-device-name] command[ count]

The -f option is used to specify the tape device file name, typically a no-rewind device file name If the -f option is omitted, the value of the TAPE environment variable is used to determine the tape device to manipulate

Commands

status Displays status information about the tape drive

rewind Rewinds the tape

retension Rewinds the cartridge tape completely, winds

the tape forward to the end of the tape, then rewinds back to the beginning of the tape to smooth out the tape tension

erase Erases the entire tape

fsf Forward skips count tape files

bsf Backward skips count tape files

eom Skips to the end of the recorded media

off Ejects 4- or 8-mm tapes

Note – Only the unique prefix of a command is required For example,

use ret in place of retension

Use the following mt command to rewind a tape:

$ mt rew

To have the tape skip forward a tape file, use the following command:

$ mt -f /dev/rmt/0n fsf 1

The device name /dev/rmt/0n tells the tape drive not to rewind the tape after it has performed a function This device naming convention can also be used when archiving files with tar and jar

Note – The retension option does not work with 8-mm tapes.

Backing up and Restoring the Home Directory

Backing up the Home Directory

Since most work is done in users’ home directories, these directories are often scheduled for backup on a nightly basis by system administrators If your home directory is not being backed up by the system administrator, it is good practice to perform a regular nightly backup of changing data

1 Create the tar file using a relative path name

$ cd /export/home

$ tar cvf /tmp/home.tar user1

2 Display the table of contents

$ tar tvf /tmp/home.tar

3 Compress the tar file

$ compress -v /tmp/home.tar

/tmp/home.tar: Compression: 80.85% replaced with /tmp/home.tar.Z

4 Change directory to /tmp Back up the compressed file on to a tape using the tar

command

$ cd /tmp

$ tar cv home.tar.Z

Restoring the Home Directory

To restore files,

1 In the home directory, make a new directory and change to it to prevent overwriting of files

$ cd

$ mkdir newhome

$ cd newhome

2 Extract the home directory from tape.

$ tar xv

3 Uncompress the file

$ uncompress home.tar.Z

4 Extract the tar file

$ tar xvf home.tar

5 Move files as needed

Exercise: Saving and Restoring Files

Exercise objective – In this exercise you will practice backing up files to tape or disk.

Tasks

Note – If you get a “Permission Denied” error while performing the following exercises, check

the write protect switch on the tape

Complete these steps:

1 Back up your home directory to a file using the tar command

2 Compress the tar file and archive it to tape

3 Use the jar utility to back up ~/practice

4 Use the tar utitlity to back up ~/practice and compress the file

5 Compare the tar and jar file backups of ~/practice for size

6 Retension the tape

Workshop Labs

Use what you have learned so far in this course to work through the following:

1 Another user in your group needs a copy of the files in your personal binary directory Create a compressed tar file, place it in that directory, and make it available to the other user

Exercise Summary

Discussion – Take a few minutes to discuss what experiences, issues, or discoveries you had

during the lab exercises

 Manage the discussion here based on the time allowed for this module, which was given in the “About This Course” module If you find you do not have time

to spend on

discussion, then just highlight the key concepts students should have learned from the lab exercise.

• Experiences

 Ask students what their overall experiences with this exercise have been You might want to go over any trouble spots or especially confusing areas at this time.

• Interpretations

 Ask students to interpret what they observed during any aspects of this exercise.

• Conclusions

 Have students articulate any conclusions they reached as a result of this exercise

experience.

• Applications

 Explore with students how they might apply what they learned in this exercise to

situations at their workplace.

Exercise Solutions

1 Back up your home directory to a file using the tar command

$ cd

$ cd

$ tar cvf /tmp/homedir.tar login-ID

$ tar tvf /tmp/homedir.tar

2 Compress the tar file and archive it to tape

$ cd /tmp

$ compress homedir.tar

$ tar cv homedir.tar.Z

3 Use the jar utility to back up your practice directory

$ cd ~

$ jar cvf ~/practice.jar practice

4 Use the tar utility to back up your practice directory and compress the file

$ cd ~

$ tar cvf ~/practice.tar practice

$ compress -v practice.tar

5 Compare the tar and jar file backups of your practice directory for size

$ ls -l *jar *tar.Z

6 Retension the tape

$ mt ret

Check Your Progress

Before continuing on to the next module, check that you are able to accomplish or answer the following:

 Use the tar and compress commands to back up files and directories

 Use the jar command to save and compress files and directories

 Position a tape to a selected data set using the mt utility

Think Beyond

What tasks do you currently complete that you can apply the tar or jar commands to, besides saving and restoring files and directories?