Stupid tar Tricks

LJ Staff — Thu, 26 Aug 2010 14:00:00 +0000

One of the most common programs on Linux systems for packaging files is the venerable tar. tar is short for tape archive, and originally, it would archive your files to a tape device. Now, you're more likely to use a file to make your archive. To use a tarfile, use the command-line option -f . To create a new tarfile, use the command-line option -c. To extract files from a tarfile, use the option -x. You also can compress the resulting tarfile via two methods. To use bzip2, use the -j option, or for gzip, use the -z option.

Instead of using a tarfile, you can output your tarfile to stdout or input your tarfile from stdin by using a hyphen (-). With these options, you can tar up a directory and all of its subdirectories by using:

tar cf archive.tar dir

Then, extract it in another directory with:

tar xf archive.tar

When creating a tarfile, you can assign a volume name with the option -V . You can move an entire directory structure with tar by executing:

tar cf - dir1 | (cd dir2; tar xf -)

You can go even farther and move an entire directory structure over the network by executing:

tar cf - dir1 | ssh remote_host "( cd /path/to/dir2; tar xf - )"

GNU tar includes an option that lets you skip the cd part, -C /path/to/dest. You also can interact with tarfiles over the network by including a host part to the tarfile name. For example:

tar cvf username@remotehost:/path/to/dest/archive.tar dir1

This is done by using rsh as the communication mechanism. If you want to use something else, like ssh, use the command-line option --rsh-command CMD. Sometimes, you also may need to give the path to the rmt executable on the remote host. On some hosts, it won't be in the default location /usr/sbin/rmt. So, all together, this would look like:

tar -c -v --rsh-command ssh --rmt-command /sbin/rmt 
 ↪-f username@host:/path/to/dest/archive.tar dir1

Although tar originally used to write its archive to a tape drive, it can be used to write to any device. For example, if you want to get a dump of your current filesystem to a secondary hard drive, use:

tar -cvzf /dev/hdd /

Of course, you need to run the above command as root. If you are writing your tarfile to a device that is too small, you can tell tar to do a multivolume archive with the -M option. For those of you who are old enough to remember floppy disks, you can back up your home directory to a series of floppy disks by executing:

tar -cvMf /dev/fd0 $HOME

If you are doing backups, you may want to preserve the file permissions. You can do this with the -p option. If you have symlinked files on your filesystem, you can dereference the symlinks with the -h option. This tells tar actually to dump the file that the symlink points to, not just the symlink.

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