Ubuntu Linux Toolbox: 1000+ Commands for Power Users (2013)
Backups and Removable Media
IN THIS CHAPTER
· Creating backup archives with tar
· Compressing backups with gzip, bzip2, and lzop
· Backing up over the network with SSH
· Doing network backups with rsync
· Making backup ISO images with mkisofs
· Burning backup images to CD or DVD with cdrecord and growisofs
Data backups in Linux were originally done by running commands to archive and compress the files to back up, and then writing that backup archive to tape. Choices for archive tools, compression techniques, and backup media have grown tremendously in recent years. Tape archiving has, for many, been replaced with techniques for backing up data over the network to other hard disks, or to CDs, DVDs, or other low-cost removable media.
This chapter details some useful tools for backing up and restoring your critical data. The first part of the chapter details how to use basic tools such as tar, gzip, and rsync for backups.
Backing Up Data to Compressed Archives
If you are coming from a Windows background, you may be used to tools such as WinZip and PKZIP, which both archive and compress groups of files in one application. Linux offers separate tools for gathering groups of files into a single archive (such as tar) and compressing that archive for efficient storage (gzip, bzip2, and lzop). However, you can also do the two steps together by using additional options to the tar command.
Creating Backup Archives with tar
The tar command, which stands for tape archiver, dates back to early UNIX systems. Although magnetic tape was the common medium that tar wrote to originally, today tar is most often used to create an archive file that can be distributed to a variety of media.
The fact that the tar command is rich in features is reflected in the dozens of options available with tar. The basic operations of tar, however, are used to create a backup archive (-c), extract files from an archive (-x), compare differences between archives (-d), and update files in an archive (-u). You can also append files to (-r or -A) or delete files from (-d) an existing archive, or list the contents of an archive (-t).
As part of the process of creating a tar archive, you can add options that compress the resulting archive. For example, add -j to compress the archive in bzip2 format or -z to compress in gzip format. By convention, regular tar files end in .tar, while compressed tar files end in .tar.bz2 (compressed with bzip2) or .tar.gz (compressed with gzip). If you compress a file manually with lzop (see www.lzop.org), the compressed tar file should end in .tar.lzo.
In addition to being used for backups, tar files are popular ways to distribute source code and binaries from software projects. That’s because you can expect every Linux and UNIX-like system to contain the tools you need to work with tar files.
Note One quirk of working with the tar command comes from the fact that tar was created before there were standards regarding how options are entered. Although you can prefix tar options with a dash, it isn’t always necessary. So you might see a command that begins tar xvf with no dashes to indicate the options.
A classic example for using the tar command might combine old-style options and pipes for compressing the output; for example:
$ tar c *.txt | gzip -c > myfiles.tar.gz Make archive, zip it and output
The example just shown illustrates a two-step process you might find in documentation for old UNIX systems. The tar command creates (c) an archive from all .txt files in the current directory. The output is piped to the gzipcommand and output to stdout (-c), and then redirected to the myfiles.tar.gz file. Note that tar is one of the few commands that doesn’t require that options be preceded by a dash (-).
New tar versions, on modern Linux systems, can create the archive and compress the output in one step:
$ tar czf myfiles.tar.gz *.txt Create gzipped tar file of .txt files
$ tar czvf myfiles.tar.gz *.txt Be more verbose creating archive
In the examples just shown, note that the new archive name (myfiles.tar.gz) must immediately follow the f option to tar (which indicates the name of the archive). Otherwise, the output from tar will be directed to stdout (in other words, your screen). The z option says to do gzip compression, and v produces verbose descriptions of processing.
When you want to return the files to a filesystem (unzipping and untarring), you can also do that as either a one-step or two-step process, using the tar command and optionally the gunzip command:
$ gunzip -c myfiles.tar.gz | tar x Unzips and untars archive
Or try the following command line instead:
$ gunzip myfiles.tar.gz ; tar xf myfiles.tar Unzips then untars archive
To do that same procedure in one step, you could use the following command:
$ tar xzvf myfiles.tar.gz
The result of the previous commands is that the archived .txt files are copied from the archive to the current directory. The x option extracts the files, z uncompresses (unzips) the files, v makes the output, and f indicates that the next option is the name of the archive file (myfiles.tar.gz).
Using Compression Tools
Compression is an important aspect of working with backup files. It takes less disk space on your backup medium (CD, DVD, tape, and so on) or server to store compressed files. It also takes less time to transfer the archives to the media or download the files over a network.
While compression can save a lot of storage space and transfer times, it can significantly increase your CPU usage. You can consider using hardware compression on a tape drive (see www.amanda.org/docs/faq.html#id346016).
In the examples shown in the previous section, tar calls the gzip command. But tar can work with many compression tools. Out of the box on Ubuntu, tar will work with gzip and bzip2. A third compression utility you can add to your toolbox is the lzop command, which can be used with tar in a different way. The order of these tools from fastest/least compression to slowest/most compression is: lzop, gzip, and bzip2.
If you are archiving and compressing large amounts of data, the time it takes to compress your backups can be significant. So you should be aware that, in general, bzip2 may take about 10 times longer than lzop and only give you twice the compression. However, with each compression command, you can choose different compression levels, to balance the need for more compression with the time that compression takes.
To use the tar command with bzip2 compression, use the -j option:
$ tar cjvf myfiles.tar.bz2 *.txt Create archive, compress with bzip2
You can also uncompress (-j) a bzip2 compressed file as you extract files (-x) using the tar command:
$ tar xjvf myfiles.tar.bz2 Extract files, uncompress bzip2 compression
The lzop compression utility is a bit less integrated into tar. Before you can use lzop, you might need to install the lzop package. To do lzop compression, you need the --use-compress-program option:
$ sudo apt-get install lzop
$ tar --use-compress-program=lzop -cf myfiles.tar.lzo *.txt
$ tar --use-compress-program=lzop -xf myfiles.tar.lzo
In the previous examples, the command line reverses the old syntax of tar with a switch before the command. For normal use and in other examples, I used the modern syntax of tar with no switch.
Note You may encounter .rar compressed files in the RAR format. This format seems to be popular in the world of peer-to-peer networks. RAR is a proprietary format so there is no widespread compressing tool. On Ubuntu, you can install the unrar and rar packages to get commands to work with RAR-format files.
Compressing with gzip
As noted, you can use any of the compression commands alone (as opposed to within the tar command line). Here are some examples of the gzip command to create and work with gzip-compressed files:
$ gzip myfile gzips myfile and renames it myfile.gz
The following command provides the same result, with verbose output:
$ gzip -v myfile gzips myfile with verbose output
myfile: 86.0% -- replaced with myfile.gz
$ gzip -tv myfile.gz Tests integrity of gzip file
$ gzip -lv myfile.gz Get detailed info about gzip file
method crc date time compressed uncompressed ratio uc_name
defla 0f27d9e4 Jul 10 04:48 46785 334045 86.0% myfile
Use any one of the following commands to compress all files in a directory:
$ gzip -rv mydir Compress all files in a directory
mydir/file1: 39.1% -- replaced with mydir/file1.gz
mydir/file2: 39.5% -- replaced with mydir/file2.gz
$ gzip -1 myfile Fastest compression time, least compression
$ gzip -9 myfile Slowest compression time, most compression
Add a dash before a number from 1 to 9 to set the compression level. As illustrated, -1 is the fastest (least) and -9 is the slowest (most) compression. The default for gzip is level 6. The lzop command has fewer levels: 1, 3 (default), 7, 8, and 9. Compression levels for bzip2 behave differently.
To uncompress a gzipped file, you can use the gunzip command. Use either of the following examples:
$ gunzip -v myfile.gz Unzips myfile.gz and renames it myfile
myfile.gz: 86.0% -- replaced with myfile
$ gzip -dv myfile.gz Same as previous command line
Although the examples just shown refer to zipping regular files, the same options can be used to compress tar archives.
Compressing with bzip2
The bzip2 command is considered to provide the highest compression among the compression tools described in this chapter. Here are some examples of bzip2:
$ bzip2 myfile Compresses file and renames it myfile.bz2
$ bzip2 -v myfile Same as previous command, but more verbose
myfile: 9.529:1, 0.840 bits/byte, 89.51% saved, 334045 in, 35056 out.
$ bunzip2 myfile.bz2 Uncompresses file and renames it myfile
$ bzip2 -d myfile.bz2 Same as previous command
$ bunzip2 -v myfile.bz2 Same as previous command, but more verbose
Compressing with lzop
The lzop command behaves differently from gzip and bzip2. The lzop command is best in cases where compression speed is more important than the resulting compression ratio. When lzop compresses the contents of a file, it leaves the original file intact (unless you use -U) but creates a new file with an .lzo suffix. Use either of the following examples of the lzop command to compress a file called myfile:
$ lzop -v myfile Leave myfile, create compressed myfile.lzo
compressing myfile into myfile.lzo
$ lzop -U myfile Remove myfile, create compressed myfile.lzo
With myfile.lzo created, choose any of the following commands to test, list, or uncompress the file:
$ lzop -t myfile.lzo Test the compressed file's integrity
$ lzop --info myfile.lzo List internal header for each file
$ lzop -l myfile.lzo List compression info for each file
method compressed uncompr. ratio uncompressed_name
LZO1X-1 59008 99468 59.3% myfile
$ lzop --ls myfile.lzo Show contents of compressed file as ls -l
$ cat myfile | lzop > x.lzo Compress standin and direct to stdout
$ lzop -dv myfile.lzo Leave myfile.lzo, make uncompressed myfile
Unlike gzip and bzip2, lzop has no related command for unlzopping. Always just use the -d option to lzop to uncompress a file. If fed a list of file and directory names, the lzop command will compress all files and ignore directories. The original filename, permission modes, and timestamps are used on the compressed file as were used on the original file.
Listing, Joining, and Adding Files to tar Archives
So far, all you’ve done with tar is create and unpack archives. There are also options for listing the contents of archives, joining archives, adding files to an existing archive, and deleting files from an archive.
To list an archive’s contents, use the -t option:
$ tar tvf myfiles.tar List files from uncompressed archive
-rw-r--r-- root/root 9584 2007-07-05 11:20:33 textfile1.txt
-rw-r--r-- root/root 9584 2007-07-09 10:23:44 textfile2.txt
$ tar tzvf myfiles.tgz List files from gzip compressed archive
If the archive were a tar archive compressed with lzop and named myfile.tar.lzo, you could list that tar/lzop file’s contents as follows:
$ tar --use-compress-program=lzop -tf myfiles.tar.lzo List lzo archives
To concatenate one tar file to another, use the -A option. The following command results in the contents of archive2.tar being added to the archive1.tar archive:
$ tar -Af archive1.tar archive2.tar
Use the -r option to add one or more files to an existing archive. In the following example, myfile is added to the archive.tar archive file:
$ tar rvf archive.tar myfile Add a file to a tar archive
You can use wildcards to match multiple files to add to your archive:
$ tar rvf archive.tar *.txt Add multiple files to a tar archive
Deleting Files from tar Archives
If you have a tar archive file on your hard disk, you can delete files from that archive. Note that you can’t use this technique to delete files from tar output on magnetic tape. Here is an example of deleting files from a tar archive:
$ tar --delete file1.txt -f myfile.tar Delete file1.txt in myfile.tar
Backing Up over Networks
After you have backed up your files and gathered them into a tar archive, what do you do with that archive? The primary reason for having a backup is in case something happens (such as a hard disk crash) where you need to restore files from that backup. Methods you can employ to keep those backups safe include:
· Copying backups to removable media such as tape, CD, or DVD (as described later in this chapter)
· Copying them to another machine over a network
Fast and reliable networks, inexpensive high-capacity hard disks, and the security that comes with moving your data off-site have all made network backups a popular practice. For an individual backing up personal data or a small office, combining a few simple commands may be all you need to create efficient and secure backups. This approach represents a direct application of the UNIX philosophy: joining together simple programs that do one thing to get a more complex job done.
Although just about any command that can copy files over a network can be used to move your backup data to a remote machine, some utilities are especially good for the job. Using OpenSSH tools such as ssh and scp, you can set up secure password-less transfers of backup archives and encrypted transmissions of those archives.
Tools such as the rsync command can save resources by backing up only files (or parts of files) that have changed since the previous backup. With tools such as unison, you can back up files over a network from Windows as well as Linux systems.
The following sections describe some of these techniques for backing up your data to other machines over a network.
Note A similar tool that might interest you is the rsnapshot command. The rsnapshot command (www.rsnapshot.org) can work with rsync to make configurable hourly, daily, weekly, or monthly snapshots of a filesystem. It uses hard links to keep a snapshot of a filesystem, which it can then sync with changed files.
Install this tool with the following commands:
$ sudo apt-get install rsnapshot
$ sudo apt-get install sshfs
Backing Up tar Archives over ssh
OpenSSH (www.openssh.org) provides tools to securely do remote login, remote execution, and remote file copy over network interfaces. By setting up two machines to share encryption keys, you can transfer files between those machines without entering passwords for each transmission. That fact lets you create scripts to back up your data from an SSH client to an SSH server without any manual intervention.
From a central Linux system, you can gather backups from multiple client machines using OpenSSH commands. The following example runs the tar command on a remote site (to archive and compress the files), pipes the tar stream to standard output, and uses the ssh command to catch the backup locally (over ssh) with tar:
$ mkdir mybackup ; cd mybackup
$ ssh chris@server1 'tar cf - myfile*' | tar xvf -
chris@server1's password: ******
In the example just shown, all files beginning with myfile are copied from the home directory of chris on server1 and placed in the current directory. Note that the left side of the pipe creates the archive and the right side expands the files from the archive to the current directory. (Keep in mind that ssh will overwrite local files if they exist, which is why you created an empty directory in the example.)
To reverse the process and copy files from the local system to the remote system, you can run a local tar command first. This example, however, adds a cd command to put the files in the /home/chris/myfolder directory on the remote machine:
$ tar cf - myfile* | ssh chris@server1 \
'cd /home/chris/myfolder; tar xvf -'
chris@server1's password: ******
In this next example, you’re not going to untar the files on the receiving end, but instead write the results to tgz files:
$ ssh chris@server1 'tar czf - myfile*' | cat > myfiles.tgz
$ tar cvzf - myfile* | ssh chris@server1 'cat > myfiles.tgz'
The first example takes all files beginning with myfile from the chris user’s home directory on server1, tars and compresses those files, and directs those compressed files to the myfiles.tgz file on the local system. The second example does the reverse by taking all files beginning with myfile in the local directory and sending them to a myfiles.tgz file on the remote system.
The examples just shown are good for copying files over the network. In addition to providing compression, they also enable you to use any tar features you choose, such as incremental backup features.
Backing Up Files with rsync
A more feature-rich command for doing backups is rsync. What makes rsync so unique is the rsync algorithm, which compares the local and remote files one small block at a time using checksums, and only transfers the blocks that are different. This algorithm is so efficient that it has been reused in many backup products.
The rsync command can work either on top of a remote shell (ssh) or by running an rsyncd daemon on the server end. The following example uses rsync over ssh to mirror a directory:
$ rsync -avz --delete chris@server1:/home/chris/pics/ chrispics/
The command just shown is intended to mirror the remote directory structure (/home/chris/pics/) on the local system. The -a says to run in archive mode (recursively copying all files from the remote directory), the -z option compresses the files, and -v makes the output verbose. The --delete tells rsync to delete any files on the local system that no longer exist on the remote system.
For ongoing backups, you can have rsync do seven-day incremental backups. Here’s an example:
# mkdir /var/backups
# rsync --delete --backup \
--backup-dir=/var/backups/backup-`date +%A` \
-avz chris@server1:/home/chris/Personal/ \
When the command just shown runs, all the files from /home/chris/Personal on the remote system server1 are copied to the local directory /var/backups/current-backup. All files modified today are copied to a directory named after today’s day of the week, such as /var/backups/backup-Monday. Over a week, seven directories will be created that reflect changes over each of the past seven days.
Another trick for rotated backups is to use hard links instead of multiple copies of the files. This two-step process consists of rotating the files, and then running rsync:
# rm -rf /var/backups/backup-old/
# mv /var/backups/backup-current/ /var/backups/backup-old/
# rsync --delete --link-dest=/var/backups/backup-old -avz \
In the previous procedure, the existing backup-current directory replaces the backup-old directory, deleting the two-week-old full backup with last week’s full backup. When the new full backup is run with rsync using the --link-dest option, if any of the files being backed up from the remote Personal directory on server1 existed during the previous backup (now in backup-old), a hard link is created between the file in the backup-current directory and backup-old directory.
You can save a lot of space by having hard links between files in your backup-old and backup-current directory. For example, if you had a file named file1.txt in both directories, you could check that both were the same physical file by listing the files’ inodes as follows:
$ ls -i /var/backups/backup*/file1.txt
Backing Up with unison
Although the rsync command is good to back up one machine to another, it assumes that the machine being backed up is the only one where the data is being modified. What if you have two machines that both modify the same file and you want to sync those files? Unison is a tool that will let you do that.
It’s common for people to want to work with the same documents on their laptop and desktop systems. Those machines might even run different operating systems. Because unison is a cross-platform application, it can let you sync files that are on both Linux and Windows systems. To use unison in Ubuntu, you must install the unison package (type the sudo apt-get install unison command). Both systems you are syncing must run the same version of unison.
With unison, you can define two roots representing the two paths to synchronize. Those roots can be local or remote over ssh. For example:
$ unison /home/chris ssh://chris@server1//home/cnegus
$ unison /home/chris /mnt/backups/chris-homedir
Unison contains both graphical and command-line tools for doing unison backups. It will try to run the graphical version by default. This may fail if you don’t have a desktop running or if you’re launching unison from within screen. To force unison to run in command line mode, add the -ui text option as follows:
$ unison /home/chris ssh://chris@server1//home/cnegus -ui text
Looking for changes
Waiting for changes from server
newfile ----> memo.txt [f] y
The unison utility will then compare the two roots and for each change that occurred since last time, ask you what you want to do. In the preceding example, there’s a new file called memo.txt on the local system. You are asked if you want to proceed with the update (in this case, copy memo.txt from the local machine to server1). Type y to do the updates.
If you trust unison, add -auto to make it take default actions without prompting you:
$ unison /home/chris ssh://chris@server1//home/cnegus -auto
For more information, see the man page for unison. In addition, you can view unison options using the -help option. You can also display and page through the unison manual using the -doc all option as shown here:
$ unison -help See unison options
$ unison -doc all | less Display unison manual
If you find yourself synchronizing two roots frequently, you can create a profile, which is a series of presets. In graphical mode, the default screen makes you create profiles. Profiles are stored in .prf text files in the ~/.unison/directory. They can be as simple as the following:
root = /home/chris
root = ssh://chris@server1//home/cnegus
If this is stored in a profile called cn-home.prf, you can invoke it simply with the following command line:
$ unison cn-home
Backing Up to Removable Media
The capacity of CDs and DVDs, and the low costs of those media, has made them attractive options as computer backup media. Using tools that commonly come with Linux systems, you can gather files to back up into CD or DVD images and burn those images to the appropriate media.
Command line tools such as mkisofs (for creating CD images) and cdrecord (for burning images to CD or DVD) once provided the most popular interfaces for making backups to CD or DVD. Now there are many graphical front-ends to those tools you could also consider using. For example, GUI tools for mastering and burning CDs/DVDs include K3b (the KDE CD and DVD Kreator) and Nautilus (GNOME’s file manager that offers a CD-burning feature). Other GUI tools for burning CDs include gcombust, X-CD-Roast, and graveman.
The commands for creating filesystem images to back up to CD or DVD, as well as to burn those images, are described in this section.
Creating Backup Images with mkisofs
Most data CDs and DVDs can be accessed on both Windows and Linux systems because they are created using the ISO9660 standard for formatting the information on those discs. Because most modern operating systems need to save more information about files and directories than the basic ISO9660 standard includes, extensions to that standard were added to contain that information.
Using the mkisofs command, you can back up the file and directory structure from any point in your Linux filesystem and produce an ISO9660 image. That image can include the following kinds of extensions:
· System Use Sharing Protocol (SUSP) extensions are records identified in the Rock Ridge Interchange Protocol. SUSP records can include UNIX-style attributes, such as ownership, long filenames, and special files (such as character devices and symbolic links).
· Joliet directory records store longer filenames in a form that makes them usable to Windows systems.
· Hierarchical File System (HFS) extensions allow the ISO image to appear as an HFS filesystem, which is the native filesystem for Macintosh computers. Likewise, Data and Resource forks can be added in different ways to be read by Macs.
When you set out to create your ISO image, consider where you will ultimately need to access the files you back up using mkisofs (Linux, Windows, or Mac). Once the image is created, it can be used in different ways, the most obvious of which is to burn the image to a CD or DVD.
Besides being useful in producing all or portions of a Linux filesystem to use on a portable medium, mkisofs is also useful for creating live CDs/DVDs. It does this by adding boot information to the image that can launch a Linux kernel or other operating system, bypassing the computer’s hard drive.
Note Although you can still use the mkisofs command in Ubuntu, mkisofs is now a pointer to genisoimage. The genisoimage command was derived from mkisofs, which was part of the cdrtools package (see http://cdrecord.berlios.de). Development of genisoimage is part of the cdrkit project (www.cdrkit.org). Type apt-get install genisoimage to install that package.
Because most Linux users store their personal files in their home directories, a common way to use mkisofs to back up files is to back up everything under the /home directory. Here are some examples of using mkisofs to create an ISO image from all files and directories under the /home directory:
$ cd /tmp
$ sudo mkisofs -o home.iso /home Create basic ISO9660 image
$ sudo mkisofs -o home2.iso -J -R /home Add Joliet Rock Ridge extns
$ sudo mkisofs -o home3.iso -J -R -hfs /home Also add HFS extensions
With the last command, you will see a warning message like the following:
genisoimage: Warning: no Apple/Unix files will be decoded/mapped
In each of the three examples, all files and directories beneath the /home directory are added to the ISO image (home.iso). The first example has no extensions, so all filenames are converted to DOS-style naming (8.3 characters). The second example uses Joliet and Rock Ridge extensions, so filenames and permissions should appear as they did on the original Linux system when you open the ISO on a Linux or Windows system. The last example also makes the files on the image readable from a Mac filesystem.
Note You can also read Rock Ridge and Joliet extensions on Mac OS X.
You can have multiple sources added to the image. Here are some examples:
$ mkisofs -o home.iso -R -J music/ docs/ \ Multiple directories/files
$ mkisofs -o home.iso -J -R \ Graft files on to the image
-graft-points Pictures/=/usr/share/pixmaps/ \
The first example in the preceding code shows various files and directories being combined and placed on the root of the ISO image. The second example grafts the contents of the /usr/share/pixmaps directory into the /home/chris/Pictures directory. As a result, on the CD image the /Pictures directory will contain all content from the /usr/share/pixmaps directory.
Adding information into the header of the ISO image can help you identify the contents of that image later. This is especially useful if the image is being saved or distributed online, without a physical disc you can write on. Here are some examples:
$ mkisofs -o /tmp/home.iso -R -J \ Add header info to ISO
-p www.handsonhistory.com \
-publisher "Swan Bay Folk Art Center" \
-V "WebBackup" \
-A "mkisofs" \
-volset "1 of 4 backups, July 30, 2013" \
In the preceding example, -p indicates the preparer ID, which could include a phone number, mailing address, or website for contacting the preparer of the ISO image. With the option -publisher, you can indicate a 128-character description of the preparer (possibly the company or organization name).
The -V indicates the volume ID. Volume ID is important because in many Linux systems this volume ID is used to mount the CD when it is inserted. For example, in the command line just shown, the CD would be mounted on /media/WebBackup in Ubuntu and other Linux systems. The -A option can be used to indicate the application used to create the ISO image. The -volset option can contain a string of information about a set of ISO images.
When you have created your ISO image, and before you burn it to disc, you can check the image and make sure you can access the files it contains. Here are ways to check it out:
$ volname home.iso Display volume name
$ isoinfo -d -i home.iso Display header information
CD-ROM is in ISO 9660 format
System id: LINUX
Volume id: WebBackup
Volume set id: All Website material on November 2, 2013
Publisher id: Swan Bay Folk Art Center
Data preparer id: www.handsonhistory.com
Application id: mkisofs
Copyright File id:
Abstract File id:
Bibliographic File id:
Volume set size is: 1
Volume set sequence number is: 1
Logical block size is: 2048
Volume size is: 23805
Joliet with UCS level 3 found
Rock Ridge signatures version 1 found
You can see a lot of the information entered on the mkisofs command line when the image was created. If this had been an image that was going to be published, you might also have indicated the locations on the CD of a copyright file (-copyright), abstract file (-abstract), and bibliographic file (-biblio). Provided that the header is okay, you can next try accessing files on the ISO image by mounting it:
$ sudo mkdir /mnt/myimage Create a mount point
$ sudo mount -o loop home.iso /mnt/myimage Mount the ISO in loopback
$ ls -l /mnt/myimage Check the ISO contents
$ sudo umount /mnt/myimage Unmount image when done
Note The ISO image is mounted read-only. If you want to work with the contents, you need to copy the files and directories you want to another directory.
Besides checking that you can access the files and directories on the ISO, make sure that the date/time stamps, ownership, and permissions are set as you would like. That information might be useful if you need to restore the information at a later date.
Burning Backup Images with cdrecord
The cdrecord command is the most popular Linux command line tool for burning CD and DVD images. After you have created an ISO image (as described earlier) or obtained one otherwise (such as downloading an install CD or live CD from the Internet), cdrecord makes it easy to put that image on a disc.
Note In Ubuntu, cdrecord has been replaced with the wodim command. The wodim command was created from the cdrecord code base and still supports most of the same options. If you run cdrecord, you will actually be running wodim in this Ubuntu release. If you have problems with that utility, contact the CDRkit project (http://cdrkit.org). Type apt-get install wodem to install the package, if it isn’t already installed.
There is no difference in making a CD or DVD ISO image, aside from the fact that a DVD image can obviously be bigger than a CD image. Check the media you have for their capacities. A CD can typically hold 650MB, 700MB, or 800MB, whereas mini CDs can hold 50MB, 180MB, 185MB, or 193MB. Single-layer DVDs hold 4.7GB, while double-layer DVDs can hold 8.4GB.
Note Keep in mind, however, that CD/DVD manufacturers list their capacities based on 1000KB per 1MB, instead of 1024KB. Type du --si home.iso to list the size of your ISO, instead of du -sh as you would normally, to check if your ISO will fit on the media you have.
Before you begin burning your image to CD or DVD, check that your drive supports CD/DVD burning and determine the address of the drive. Use the --scanbus option to cdrecord to do that:
$ cdrecord --scanbus Shows a drive that cannot do burning
0,0,0 0) 'SAMSUNG ' 'DVD-ROM SD-616E ' 'F503' Removable CD-ROM
0,0,0 1) *
0,0,0 2) *
$ cdrecord --scanbus Shows a drive that can burn CDs or DVDs
0,0,0 0) 'LITE-ON ' 'DVDRW SOHW-1633S' 'BS0C' Removable CD-ROM
0,0,0 1) *
0,0,0 2) *
In the two examples shown, the first indicates a CD/DVD drive that only supports reading and cannot burn CDs (DVD-ROM and CD-ROM). The second example shows a drive that can burn CDs or DVDs (DVDRW). Insert the medium you want to record on. Assuming your drive can burn the media you have, here are some simple cdrecord commands for burning a CD or DVD images:
$ cdrecord -dummy home.iso Test burn without actually burning
$ cdrecord -v home.iso Burn CD (default settings) in verbose
$ cdrecord -v speed=24 home.iso Set specific speed
$ cdrecord -pad home.iso Can't read track, add 15 zeroed sectors
$ cdrecord -eject home.iso Eject CD/DVD when burn is done
$ cdrecord /dev/cdrw home.iso Identify drive by dev name (may differ)
$ cdrecord dev=0,2,0 home.iso Identify drive by SCSI name
The cdrecord command can also burn multi-session CDs/DVDs. Here is an example:
$ cdrecord -multi home.iso Start a multi-burn session
$ cdrecord -msinfo Check the session offset for next burn
Using /dev/cdrom of unknown capabilities
$ mkisofs -J -R -o new.iso \ Create a second ISO to burn
-C 0,93041 /home/chris/more Indicate start point and new data for ISO
$ cdrecord new.iso Burn new data to existing CD
You can use multiple -multi burns until the CD is filled up. For the final burn, don’t use -multi so that the CD will be closed.
Making and Burning DVDs with growisofs
Using the growisofs command, you can combine the two steps of gathering files into an ISO image (mkisofs) and burning that image to DVD (cdrecord). Besides saving a step, the growisofs command also offers the advantage of keeping a session open by default until you close it, so you don’t need to do anything special for multi-burn sessions.
Here is an example of some growisofs commands for a multi-burn session:
$ growisofs -Z /dev/dvd -R -J /home/chris Master and burn to DVD
$ growisofs -Z /dev/dvd -R -J /home/chris Add to burn
$ growisofs -M /dev/dvd=/dev/zero Close burn
If you want to add options when creating the ISO image, you can simply add mkisofs options to the command line. (For example, see how the -R and -J options are added in the preceding examples.)
If you want to burn a DVD image using growisofs, you can use the -dvd-compat option. Here’s an example:
$ growisofs -dvd-compat -Z /dev/dvd=image.iso Burn an ISO image to DVD
The -dvd-compat option can improve compatibility with different DVD drives over some multi-session DVD burning procedures.
Linux and its predecessor UNIX systems handled data backups by combining commands that each handled a discrete set of features. Backups of your critical data can still be done in this way. In fact, many of the tools you can use will perform more securely and efficiently than ever before.
The tape archiver utility (tar command) has expanded well beyond its original job of making magnetic tape backups of data files. Because nearly every Linux and UNIX system includes tar, it has become a standard utility for packaging software and backing up data to compressed archives. Those archives can then be transported and stored in a variety of ways.
To move backed up data to other machines over a network, you can use remote execution features of OpenSSH tools (such as ssh). You can also use an excellent utility called rsync. With rsync, you can save resources by only backing up files (or parts of files) that have changed.
Inexpensive CDs and DVDs have made those media popular for doing personal and small-office backups. The mkisofs command can create filesystems of backed up data in ISO9660 format that can be restored on a variety of systems (Linux, Windows, or Mac). Once the mkisofs command has created an ISO image, the image can be burned to CD or DVD using the cdrecord or growisofs command.