CPIO 文件格式

http://www.mkssoftware.com/docs/man4/cpio.4.asp

DESCRIPTION

This document describes the format of archives read and written by the cpio utility. A cpio archive consists of the concatenation of one or more member files. Each member file contains a header (as described later in this reference page) optionally followed by file contents as indicated in the header. The end of the archive is indicated by another header describing an (empty) file named TRAILER!!.

There are two types of cpio archives, differing only in the style of the header. ASCII archives have totally printable header information; thus, if the files being archived are also ASCII files, the whole archive is ASCII. By default, cpio writes archives with binary headers.

The information in ASCII archive headers is stored in fixed-width, octal (base 8) numbers zero-padded on the left. Table 1 gives the order and field width for the information in the ASCII header.

Field Width	Field Name	Meaning
6	magic	magic number "070707"
6	dev	device where file resides
6	ino	I-number of file
6	mode	file mode
6	uid	owner user ID
6	gid	owner group ID
6	nlink	number of links to file
6	rdev	device major/minor for special file
11	mtime	modify time of file
6	namesize	length of file name
11	filesize	length of file to follow

Table 1: ASCII Header Format for cpio File

Most of this information is compatible with that returned by the UNIX stat() function; see also stat. After this information, namesize bytes of path name is stored. namesize includes the null byte of the end of the path name. After this, filesize bytes of the file contents are recorded.

Binary headers contain the same information in 2 byte (short) and 4 byte (long) integers as shown in Table 2.

Bytes	Field Name
2	magic
2	dev
2	ino
2	mode
2	uid
2	gid
2	nlink
2	rdev
4	mtime
2	namesize
4	filesize

Table 2: Binary Header Format for cpio File

After this information comes the file name (with namesize rounded up to the nearest 2 byte boundary). Then the file contents appear as in the ASCII archive. The byte ordering of the 2 and 4 byte integers in the binary format is machine dependent and thus portability of this format is not easily guaranteed.

---

PORTABILITY

cpio archives are fully compatible between UNIX and Windows systems. For maximum portability among different system architectures, only the ASCII archive format should be used.

Because the Windows file systems lack many features of the UNIX file system, much of the header information is meaningless.

---

AVAILABILITY

MKS Toolkit for System Administrators
MKS Toolkit for Developers
MKS Toolkit for Interoperability
MKS Toolkit for Professional Developers
MKS Toolkit for Enterprise Developers
MKS Toolkit for Enterprise Developers 64-Bit Edition

---

SEE ALSO

Commands:

cpio, pax, tar

File Formats:

tar

Miscellaneous:

stat