3.4. File Compression and Archiving
It is useful to store a group of files in one file for easy backup, for transfer to another directory, or for transfer to another computer. It is also useful to compress large files; compressed files take up less disk space and download faster via the Internet.
It is important to understand the distinction between an archive file and a compressed file. An archive file is a collection of files and directories stored in one file. The archive file is not compressed — it uses the same amount of disk space as all the individual files and directories combined. A compressed file is a collection of files and directories that are stored in one file and stored in a way that uses less disk space than all the individual files and directories combined. If disk space is a concern, compress rarely-used files, or place all such files in a single archive file and compress it.
 | Note |
|---|---|
An archive file is not compressed, but a compressed file can be an archive file. |
3.4.1. Using File Roller
Red Hat Enterprise Linux includes a graphical utility called File Roller. File Roller can compress, decompress, and archive files in common Unix and Linux formats. It has a simple interface and extensive help documentation. To start File Roller, select Archive Manager from the Applications (the main menu on the panel) => System Tools sub-menu. File Roller is also integrated into the desktop environment and Nautilus.
 | Tip |
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If you are using a file manager (such as Nautilus), you can double-click the file you wish to unarchive or decompress to start File Roller. The File Roller browser window appears with the decompressed/unarchived file in a folder for you to extract or browse. |
3.4.1.1. Decompressing and Unarchiving with File Roller
To unarchive and/or decompress a file, click the Open button on the main toolbar. A file menu pops up, allowing you to choose the archive you wish to manipulate. For example, if you have a file called foo.tar.gz located in your home directory, highlight the file and click OK. The file appears in the main File Roller browser window as a folder, which you can navigate by double-clicking the folder icon. File Roller preserves all directory and subdirectory structures, which is convenient if you are looking for a particular file in the archive. You can extract individual files or entire archives by clicking the Extract button, choosing the directory in which to save the unarchived files, and clicking OK.
3.4.1.2. Creating Archives with File Roller
File Roller allows you to create archives of your files and directories. To create a new archive, click New on the toolbar. A file browser pops up, allowing you to specify an archive name and the compression technique. For example, you may choose a Tar Compressed with gzip (.tar.gz) format from the drop-down menu and type the name of the archive file you want to create. Click OK and your new archive is ready to be filled with files and directories. To add files to your new archive, click Add, which opens a browser window that you can navigate to find the file or directory to add to the archive. Click Add when you are finished, and click Archive => Close to close the archive.
| Tip |
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There is much more you can do with File Roller than is explained here. Refer to the File Roller manual (available by clicking Help => Manual) for more information. |
3.4.2. Compressing Files at the Shell Prompt
Red Hat Enterprise Linux provides the bzip2, gzip, and zip tools for compression from a shell prompt. The bzip2 compression tool is recommended because it provides the most compression and is found on most UNIX-like operating systems. The gzip compression tool can also be found on most UNIX-like operating systems. To transfer files between Linux and other operating system such as MS Windows, use zip because it is more compatible with the compression utilities available for Windows.
| Compression Tool | File Extension | Decompression Tool |
|---|---|---|
| bzip2 | .bz2 | bunzip2 |
| gzip | .gz | gunzip |
| zip | .zip | unzip |
Table 3-1. Compression Tools
By convention, files compressed with bzip2 are given the extension .bz2, files compressed with gzip are given the extension .gz, and files compressed with zip are given the extension .zip.
Files compressed with bzip2 are uncompressed with bunzip2, files compressed with gzip are uncompressed with gunzip, and files compressed with zip are uncompressed with unzip.
3.4.2.1. Bzip2 and Bunzip2
To use bzip2 to compress a file, enter the following command at a shell prompt:
bzip2 filename |
The file is compressed and saved as filename.bz2.
To expand the compressed file, enter the following command:
bunzip2 filename.bz2 |
The filename.bz2 compressed file is deleted and replaced with filename.
You can use bzip2 to compress multiple files and directories at the same time by listing them with a space between each one:
bzip2 filename.bz2 file1 file2 file3 /usr/work/school |
The above command compresses file1, file2, file3, and the contents of the /usr/work/school/ directory (assuming this directory exists) and places them in a file named filename.bz2.
| Tip |
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For more information, enter man bzip2 and man bunzip2 at a shell prompt to read the man pages for bzip2 and bunzip2. |
3.4.2.2. Gzip and Gunzip
To use gzip to compress a file, enter the following command at a shell prompt:
gzip filename |
The file is compressed and saved as filename.gz.
To expand the compressed file, enter the following command:
gunzip filename.gz |
The filename.gz compressed file is deleted and replaced with filename.
You can use gzip to compress multiple files and directories at the same time by listing them with a space between each one:
gzip -r filename.gz file1 file2 file3 /usr/work/school |
The above command compresses file1, file2, file3, and the contents of the /usr/work/school/ directory (assuming this directory exists) and places them in a file named filename.gz.
| Tip |
|---|---|
For more information, enter man gzip and man gunzip at a shell prompt to read the man pages for gzip and gunzip. |
3.4.2.3. Zip and Unzip
To compress a file with zip, enter the following command:
zip -r filename.zip filesdir |
In this example, filename.zip represents the file you are creating and filesdir represents the directory you want to put in the new zip file. The -r option specifies that you want to include all files contained in the filesdir directory recursively.
To extract the contents of a zip file, enter the following command:
unzip filename.zip |
You can use zip to compress multiple files and directories at the same time by listing them with a space between each one:
zip -r filename.zip file1 file2 file3 /usr/work/school |
The above command compresses file1, file2, file3, and the contents of the /usr/work/school/ directory (assuming this directory exists) and places them in a file named filename.zip.
| Tip |
|---|---|
For more information, enter man zip and man unzip at a shell prompt to read the man pages for zip and unzip. |
3.4.3. Archiving Files at the Shell Prompt
A tar file is a collection of several files and/or directories in one file. This is a good way to create backups and archives.
Some of tar's options include:
-c — create a new archive
-f — when used with the -c option, use the filename specified for the creation of the tar file; when used with the -x option, unarchive the specified file
-t — show the list of files in the tar file
-v — show the progress of the files being archived
-x — extract files from an archive
-z — compress the tar file with gzip
-j — compress the tar file with bzip2
To create a tar file, enter:
tar -cvf filename.tar directory/file |
In this example, filename.tar represents the file you are creating and directory/file represents the directory and file you want to put in the archived file.
You can tar multiple files and directories at the same time by listing them with a space between each one:
tar -cvf filename.tar /home/mine/work /home/mine/school |
The above command places all the files in the work and the school subdirectories of /home/mine in a new file called filename.tar in the current directory.
To list the contents of a tar file, enter:
tar -tvf filename.tar |
To extract the contents of a tar file, enter:
tar -xvf filename.tar
|
This command does not remove the tar file, but it places copies of its unarchived contents in the current working directory, preserving any directory structure that the archive file used. For example, if the tarfile contains a file called bar.txt within a directory called foo/, then extracting the archive file results in the creation of the directory foo/ in your current working directory with the file bar.txt inside of it.
Remember, the tar command does not compress the files by default. To create a tarred and bzipped compressed file, use the -j option:
tar -cjvf filename.tbz file |
tar files compressed with bzip2 are conventionally given the extension .tbz; however, sometimes users archive their files using the tar.bz2 extension.
The above command creates an archive file and then compresses it as the file filename.tbz. If you uncompress the filename.tbz file with the bunzip2 command, the filename.tbz file is removed and replaced with filename.tar.
You can also expand and unarchive a bzip tar file in one command:
tar -xjvf filename.tbz |
To create a tarred and gzipped compressed file, use the -z option:
tar -czvf filename.tgz file |
tar files compressed with gzip are conventionally given the extension .tgz.
This command creates the archive file filename.tar and compresses it as the file filename.tgz. (The file filename.tar is not saved.) If you uncompress the filename.tgz file with the gunzip command, the filename.tgz file is removed and replaced with filename.tar.
You can expand a gzip tar file in one command:
tar -xzvf filename.tgz |
| Tip |
|---|---|
Enter the command man tar for more information about the tar command. |