Backup Data

Backup Data

Determining What to Back Up

ou should consider backing up the following directories in your Linux file system:

• /etc
• /home 

• /opt
• /root 

• /var
• /srv

Notice that this strategy doesn’t back up your Linux system or its utilities. Instead, it only backs up your configuration files, your user data, your log files, and your web/ftp files.

Using tar

The tar utility has been around for a very long time and is a very commonly used Linux backup tool. The acronym “tar” stands for tape archive. The tar utility takes a list of specified files and copies them into a single archive file (.tar). The .tar file can then be compressed with the gzip utility on your Linux system, resulting in a file with a .tar.gz extension. This is called a tarball.

tar –cvf filename directory

 tar –cvf /media/usb/backup .tar /home

To restore a tar archive, simply enter tar –xvf filename. For example, to extract the archive we just created, you would enter tar –xvf /media/usb/backup.tar. 

If you want to back up to a tape drive instead of a USB drive, you could do this by replacing the filename parameter in the tar command to the device name for your tape drive. On most distributions, the first SCSI tape drive in the system is referenced through /dev/st0. Therefore, you could enter tar –cvf /dev/st0 /home if you wanted to run the same backup as in the previous example, but send it to a SCSI tape drive instead.

Using cpio

The cpio utility can also be used to make archive files just like tar. A key difference between tar and cpio is the fact that you must provide cpio with a list of files and directories to back up from the standard input. This can be done using cat to display the contents of a file or by generating a listing using find or ls.

This can be done using the find utility, discussed earlier. You could switch to /home/ tux/myproject and then enter find . –print –depth | cpio –ov > /media/usb/backup.cpio. The find utility will generate a listing of all files in the current directory. Because the –print option was used, find will print the full name of each file to the screen (the standard output). Because the –depth option was also used, find checks the contents of each directory before processing the directory itself.

If there are no subdirectories in the MyProjects directory, an easier way to do this would be to enter ls | cpio –ov > /media/usb/backup.cpio

The key here is the fact that we’ve piped the standard output from find to the standard input of cpio. The cpio utility uses this as a list of files and directories to archive. The –o option tells cpio to create a new archive. The –v option simply tells cpio to run verbosely, displaying the name of each file and directory as it’s processed. Finally, we have to redirect the standard output from cpio (the archive) to a file in the file system. This is done by entering > followed by the name of the archive file.

You can also compress a cpio archive by adding the gzip utility to the pipe[md]for example, ls | cpio –ov | gzip > /media/usb/backup.cpio.gz.

To restore files from a cpio archive, you run cpio from the shell prompt using the –i option and specifying the name of the archive to process. When you do, the archive files will be extracted into the current working directory. For example, we could extract the archive we just created by entering cpio –iv < /media/usb/backup.cpio

Using dd to Copy Data

The key difference between dd and other file copy utilities is the fact that it copies data using records. The default size for a record is 512 bytes.

Let’s first look at how you copy a file with dd. The syntax is dd if=input_fileof=output_file. Use the if= (input file) option to specify the file to be copied. Use the of= (output file) option to specify the name of the new file. Here is an example:

openSUSE:/ # dd if=/home/tux/MyProject/acpidump 

You can modify the default record size using the bs=block_size option.

Another useful feature of dd is the fact that it can create a backup copy of your hard drive’s master boot record (MBR) and partition table. 

The syntax is dd if=device_fileof=output_file bs=512 count=1