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 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: • tar • compress • jar • mt 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-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? . 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. 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