cpio (copy input and output) is both a command and an archive file format. The cpio command can create archives in several formats, including it's own binary format and the more common tar format.
It isn't often used in the 'wild'. The tar command and archive format is the most commonly used. But rpm packages contain a cpio archive. A cpio archive can be extracted from a rpm file with the rpm2cpio tool.
Extracting a cpio archive
To extract a cpio archive (in this example initrd.img) into your current directory, use
cpio -i <initrd.img
Creating a cpio archive
To create a cpio archive, run
find * | cpio -o >test.cpio
To copy all of the files, including hidden files in the current folder to /some/other/path enter:
$ find .* | cpio -pmudv /some/other/path
- Gnu Cpio project page (www.gnu.org)