CPIO Converter

CPIO (Copy In, Copy Out) is a Unix archive format dating to the PWB/UNIX system at AT&T Bell Labs in 1977, predating even the tar format. The name describes the tool's original operation: copying files in to an archive and out from an archive. CPIO stores files sequentially with per-file headers containing the filename, inode information, permissions, ownership, timestamps, and file size, followed by the file data itself. The format exists in several variants: the original binary format, the POSIX.1-defined octet-oriented (ODC) format, the SVR4 newc format with expanded device and inode fields, and the CRC variant that adds checksum verification. Unlike tar, CPIO reads the list of files to archive from standard input, making it naturally composable with find and other Unix utilities through pipes. One advantage is faithful Unix metadata preservation — CPIO records device numbers, inode information, and hard link relationships with higher fidelity than early tar implementations, making it suitable for system-level backups and device file archiving. The format's central role in Linux package management is another practical significance: the RPM package format uses CPIO as its internal payload container, meaning every RPM-based Linux installation relies on CPIO extraction. While tar has become more common for general archiving, CPIO persists in system administration, initramfs images, and package management infrastructure.