2.6.5 Archiving Directories

You can archive a directory by specifying its directory name as a file name argument to tar. The files in the directory will be archived relative to the working directory, and the directory will be re-created along with its contents when the archive is extracted.

To archive a directory, first move to its superior directory. If you have followed the previous instructions in this tutorial, you should type:

$ cd ..
$

This will put you into the directory which contains ‘practice’, i.e., your home directory. Once in the superior directory, you can specify the subdirectory, ‘practice’, as a file name argument. To store ‘practice’ in the new archive file ‘music.tar’, type:

$ tar --create --verbose --file=music.tar practice

tar should output:

practice/
practice/blues
practice/folk
practice/jazz
practice/collection.tar

Note that the archive thus created is not in the subdirectory ‘practice’, but rather in the current working directory—the directory from which tar was invoked. Before trying to archive a directory from its superior directory, you should make sure you have write access to the superior directory itself, not only the directory you are trying archive with tar. For example, you will probably not be able to store your home directory in an archive by invoking tar from the root directory; See section Absolute File Names. (Note also that ‘collection.tar’, the original archive file, has itself been archived. tar will accept any file as a file to be archived, regardless of its content. When ‘music.tar’ is extracted, the archive file ‘collection.tar’ will be re-written into the file system).

If you give tar a command such as

$ tar --create --file=foo.tar .

tar will report ‘tar: ./foo.tar is the archive; not dumped’. This happens because tar creates the archive ‘foo.tar’ in the current directory before putting any files into it. Then, when tar attempts to add all the files in the directory ‘.’ to the archive, it notices that the file ‘./foo.tar’ is the same as the archive ‘foo.tar’, and skips it. (It makes no sense to put an archive into itself.) GNU tar will continue in this case, and create the archive normally, except for the exclusion of that one file. (Please note: Other implementations of tar may not be so clever; they will enter an infinite loop when this happens, so you should not depend on this behavior unless you are certain you are running GNU tar. In general, it is wise to always place the archive outside of the directory being dumped.)

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