Archive and compress data using Linux

Behind the phrase “data archiving” is the basic idea of backing up files or entire directories and storing them in a secure location, often in a compressed form. For reasons of data security, archiving was an important factor in server environments at an early stage: Originally server data was stored on tape drives – a backup method which is still used for large data volumes. To make this archiving method as efficient as possible, the packing programme tar (short for tape archiver) was developed for Unix systems in 1979. With the help of tar, files and directories can to this day still be packed into a single data file and then recovered with the user rights still remaining intact – as long as the source and target both support the Unix or Linux data file directories.

For the archiving process to free up additional storage space, .tar-data files are often compressed with the help of different tools, like gzip, bzip2, or lzop. But what are the different compression programmes and formats? And why are they still so important today for systems like Linux tar?

There are a number of free compression tools for Linux distributions that all have one thing in common: they can be operated via command line or terminal. Short commands can quickly compress data files, such as HTML documents, to save storage space and bandwidth when sending via networks or the internet. In addition, there are standard graphic interfaces for these tools, as well as archive managers, which combine several compression programmes – that must be installed as well – into a single visual user interface. Control of the graphic interface obviously requires additional system resources, which is why use of a terminal generally remains the best choice for compression.

The main difference between the individual programmes is the compression rate, which is accompanied by different compression durations. In most cases, however, different modes can also be selected in the tool itself to offer either the best possible storage reduction or the quickest possible compression time. Another feature that differentiates compression software is the output format. Due to the different algorithms used by the various programmes, compressed files have different pack format and require specific programmes to be unpacked.

In terms of speed, the free pack programme is still among the top options, which is why common web server software such as Apache, IIS, or NGINX usually implement it in the form of their own modules to answer user queries with compressed data packets in the shortest possible time. Additional information about the functionality and use of the GPL-licensed compression tool can be found in our article on the program.

For the standard compression process it’s not necessary to specify options. This is only required if you want to change compression settings, access the overview menu, or unpack a .bz2 file. For example, to pack the text document test.txt, you just need to complete the command

to delete the original file and replace it with the compressed file test.txt.bz2. By placing the documents together, you can also package multiple files with a single command:

If you want to decompress a packed document, it’s necessary – as mentioned earlier – to set the corresponding option parameters (-d):

Here’s an overview of some other bzip2 command options:

The archiving programme tar has been in operation for over 30 years and has hardly lost any of its value. Partially, this is because the tool allows data to be archived while retaining file definitions. Mainly, though, it’s because it allows for the packing of complete file directories. This makes tar the perfect partner of compressional tools like gzip and bzip2, which only allow for single file data compression.

In the first step, the packing programme compiles all data files in a selected directory into a single archive file without unlinking any of the contained files. In the second step, the files are compressed using one of the specific compression programmes. As a result of this compression, which is either described as progressive, compact, or solid, the archive files are given extended formats, such as .tar.gz (.tgz for short) or .tar.bz2 (.tbz2 for short). The packing programme also allows for the subsequent unpacking of such files (e.g. file type .tar.gz).

The combination of tar and a compression tool isn’t required, so you can also combine files in an archive that you haven’t previously packaged or don’t want to compress. For example, if you want to bundle the uncompressed test documents test.txt and test2.txt in the same archive named archive.tar, the following command will suffice:

To unzip this archive on Linux, replace the –c (create new archive) parameter with –x (extract files from archive). If not only a certain archive component is to be unzipped, then the file(s) can be omitted:

Alternatively, if you aim to pack a compressed archive – for example, on the basis of the gzip compression, including the extended formatting .tar.gz – then tar also offers corresponding options. Since the programme has implemented options for compression and decompression with the bzip2, xz, compress, and gzip pack programmes, this is also possible with a single command:

 The command to unpack .tar.gz differs from the equivalent for uncompressed directories only through the specification of the pack programme parameter:

In addition to the previously listed command options for easy file archiving, there are several additional parameters to specify the pack or unpack process. These include the compression methods already mentioned, options for setting up directories, as well as options for checking and previewing the tar archives:

Update contents of an archive (doesn’t include subdirectories!)

Expand contents of an archive

Compare contents of an archive with the file system (run in the archive directory!)

File Roller is a graphic user interface for various compression tools and packing programmes, which is standard for the operation of command lines. The archive manager is available for the GNOME and Unity desktop environments, and has been distributed under the GNU General Public License since 2001. It allows contents of various archive files to be viewed, as well as for files to be extracted, deleted, or added to them. It is also possible to create new compressed or unchanged files and archives, as well as to convert them to another format. For this purpose, the main window of the software offers various buttons and menus alongside a drag-and-drop function. In addition to tar archive formats like tar.gz, File Roller supports the following formats:

• .7z
• .tar
• .gzip
• .bzip2
  
• .ar
• .jar
• .cpio

File Roller is preinstalled on some Linux distributions, such as Ubuntu, by default, but can also be installed manually using the respective package manager or from the official homepage. An alternative for the desktop environment KDE is Ark.