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<p>CPIO(5) BSD File Formats Manual CPIO(5)</p>

<p style="margin-top: 1em"><b>NAME</b></p>

<p style="margin-left:6%;"><b>cpio</b> &mdash; format of
cpio archive files</p>

<p style="margin-top: 1em"><b>DESCRIPTION</b></p>

<p style="margin-left:6%;">The <b>cpio</b> archive format
collects any number of files, directories, and other file
system objects (symbolic links, device nodes, etc.) into a
single stream of bytes.</p>

<p style="margin-left:6%; margin-top: 1em"><b>General
Format</b> <br>
Each file system object in a <b>cpio</b> archive comprises a
header record with basic numeric metadata followed by the
full pathname of the entry and the file data. The header
record stores a series of integer values that generally
follow the fields in <i>struct stat</i>. (See stat(2) for
details.) The variants differ primarily in how they store
those integers (binary, octal, or hexadecimal). The header
is followed by the pathname of the entry (the length of the
pathname is stored in the header) and any file data. The end
of the archive is indicated by a special record with the
pathname &rsquo;&rsquo;TRAILER!!!&rsquo;&rsquo;.</p>

<p style="margin-left:6%; margin-top: 1em"><b>PWB
format</b> <br>
XXX Any documentation of the original PWB/UNIX 1.0 format?

<p style="margin-left:6%; margin-top: 1em"><b>Old Binary
Format</b> <br>
The old binary <b>cpio</b> format stores numbers as 2-byte
and 4-byte binary values. Each entry begins with a header in
the following format:</p>

<p style="margin-left:14%; margin-top: 1em">struct
header_old_cpio { <br>
unsigned short c_magic; <br>
unsigned short c_dev; <br>
unsigned short c_ino; <br>
unsigned short c_mode; <br>
unsigned short c_uid; <br>
unsigned short c_gid; <br>
unsigned short c_nlink; <br>
unsigned short c_rdev;</p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="24%"></td>
<td width="11%">

<p>unsigned short c_mtime[2];</p></td>
<td width="65%">

<p style="margin-left:14%;">unsigned short c_namesize;</p>

<table width="100%" border="0" rules="none" frame="void"
       cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="24%"></td>
<td width="76%">

<p>unsigned short c_filesize[2];</p></td></tr>

<p style="margin-left:14%;">};</p>

<p style="margin-left:6%; margin-top: 1em">The <i>unsigned
short</i> fields here are 16-bit integer values; the
<i>unsigned int</i> fields are 32-bit integer values. The
fields are as follows</p>

<p style="margin-top: 1em"><i>magic</i></p>

<p style="margin-left:17%; margin-top: 1em">The integer
value octal 070707. This value can be used to determine
whether this archive is written with little-endian or
big-endian integers.</p>

<p style="margin-top: 1em"><i>dev</i>, <i>ino</i></p>

<p style="margin-left:17%;">The device and inode numbers
from the disk. These are used by programs that read
<b>cpio</b> archives to determine when two entries refer to
the same file. Programs that synthesize <b>cpio</b> archives
should be careful to set these to distinct values for each

<p style="margin-top: 1em"><i>mode</i></p>

<p style="margin-left:17%; margin-top: 1em">The mode
specifies both the regular permissions and the file type. It
consists of several bit fields as follows:</p>


<p style="margin-left:28%; margin-top: 1em">This masks the
file type bits.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for sockets.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for symbolic links. For symbolic links, the link body is
stored as file data.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for regular files.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for block special devices.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for directories.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for character special devices.</p>


<p style="margin-left:28%; margin-top: 1em">File type value
for named pipes or FIFOs.</p>


<p style="margin-left:28%; margin-top: 1em">SUID bit.</p>


<p style="margin-left:28%; margin-top: 1em">SGID bit.</p>


<p style="margin-left:28%; margin-top: 1em">Sticky bit. On
some systems, this modifies the behavior of executables
and/or directories.</p>


<p style="margin-left:28%; margin-top: 1em">The lower 9
bits specify read/write/execute permissions for world,
group, and user following standard POSIX conventions.</p>

<p style="margin-top: 1em"><i>uid</i>, <i>gid</i></p>

<p style="margin-left:17%;">The numeric user id and group
id of the owner.</p>

<p style="margin-top: 1em"><i>nlink</i></p>

<p style="margin-left:17%; margin-top: 1em">The number of
links to this file. Directories always have a value of at
least two here. Note that hardlinked files include file data
with every copy in the archive.</p>

<p style="margin-top: 1em"><i>rdev</i></p>

<p style="margin-left:17%; margin-top: 1em">For block
special and character special entries, this field contains
the associated device number. For all other entry types, it
should be set to zero by writers and ignored by readers.</p>

<p style="margin-top: 1em"><i>mtime</i></p>

<p style="margin-left:17%; margin-top: 1em">Modification
time of the file, indicated as the number of seconds since
the start of the epoch, 00:00:00 UTC January 1, 1970. The
four-byte integer is stored with the most-significant 16
bits first followed by the least-significant 16 bits. Each
of the two 16 bit values are stored in machine-native byte

<p style="margin-top: 1em"><i>namesize</i></p>

<p style="margin-left:17%;">The number of bytes in the
pathname that follows the header. This count includes the
trailing NUL byte.</p>

<p style="margin-top: 1em"><i>filesize</i></p>

<p style="margin-left:17%;">The size of the file. Note that
this archive format is limited to four gigabyte file sizes.
See <i>mtime</i> above for a description of the storage of
four-byte integers.</p>

<p style="margin-left:6%; margin-top: 1em">The pathname
immediately follows the fixed header. If the <b>namesize</b>
is odd, an additional NUL byte is added after the pathname.
The file data is then appended, padded with NUL bytes to an
even length.</p>

<p style="margin-left:6%; margin-top: 1em">Hardlinked files
are not given special treatment; the full file contents are
included with each copy of the file.</p>

<p style="margin-left:6%; margin-top: 1em"><b>Portable
ASCII Format</b> <br>
Version&nbsp;2 of the Single UNIX Specification
(&rsquo;&rsquo;SUSv2&rsquo;&rsquo;) standardized an ASCII
variant that is portable across all platforms. It is
commonly known as the &rsquo;&rsquo;old
character&rsquo;&rsquo; format or as the
&rsquo;&rsquo;odc&rsquo;&rsquo; format. It stores the same
numeric fields as the old binary format, but represents them
as 6-character or 11-character octal values.</p>

<p style="margin-left:14%; margin-top: 1em">struct
cpio_odc_header { <br>
char c_magic[6]; <br>
char c_dev[6]; <br>
char c_ino[6]; <br>
char c_mode[6]; <br>
char c_uid[6]; <br>
char c_gid[6]; <br>
char c_nlink[6]; <br>
char c_rdev[6]; <br>
char c_mtime[11]; <br>
char c_namesize[6]; <br>
char c_filesize[11]; <br>

<p style="margin-left:6%; margin-top: 1em">The fields are
identical to those in the old binary format. The name and
file body follow the fixed header. Unlike the old binary
format, there is no additional padding after the pathname or
file contents. If the files being archived are themselves
entirely ASCII, then the resulting archive will be entirely
ASCII, except for the NUL byte that terminates the name

<p style="margin-left:6%; margin-top: 1em"><b>New ASCII
Format</b> <br>
The &quot;new&quot; ASCII format uses 8-byte hexadecimal
fields for all numbers and separates device numbers into
separate fields for major and minor numbers.</p>

<p style="margin-left:14%; margin-top: 1em">struct
cpio_newc_header { <br>
char c_magic[6]; <br>
char c_ino[8]; <br>
char c_mode[8]; <br>
char c_uid[8]; <br>
char c_gid[8]; <br>
char c_nlink[8]; <br>
char c_mtime[8]; <br>
char c_filesize[8]; <br>
char c_devmajor[8]; <br>
char c_devminor[8]; <br>
char c_rdevmajor[8]; <br>
char c_rdevminor[8]; <br>
char c_namesize[8]; <br>
char c_check[8]; <br>

<p style="margin-left:6%; margin-top: 1em">Except as
specified below, the fields here match those specified for
the old binary format above.</p>

<p style="margin-top: 1em"><i>magic</i></p>

<p style="margin-left:17%; margin-top: 1em">The string

<p style="margin-top: 1em"><i>check</i></p>

<p style="margin-left:17%; margin-top: 1em">This field is
always set to zero by writers and ignored by readers. See
the next section for more details.</p>

<p style="margin-left:6%; margin-top: 1em">The pathname is
followed by NUL bytes so that the total size of the fixed
header plus pathname is a multiple of four. Likewise, the
file data is padded to a multiple of four bytes. Note that
this format supports only 4 gigabyte files (unlike the older
ASCII format, which supports 8 gigabyte files).</p>

<p style="margin-left:6%; margin-top: 1em">In this format,
hardlinked files are handled by setting the filesize to zero
for each entry except the last one that appears in the

<p style="margin-left:6%; margin-top: 1em"><b>New CRC
Format</b> <br>
The CRC format is identical to the new ASCII format
described in the previous section except that the magic
field is set to &rsquo;&rsquo;070702&rsquo;&rsquo; and the
<i>check</i> field is set to the sum of all bytes in the
file data. This sum is computed treating all bytes as
unsigned values and using unsigned arithmetic. Only the
least-significant 32 bits of the sum are stored.</p>

<p style="margin-left:6%; margin-top: 1em"><b>HP
variants</b> <br>
The <b>cpio</b> implementation distributed with HPUX used
XXXX but stored device numbers differently XXX.</p>

<p style="margin-left:6%; margin-top: 1em"><b>Other
Extensions and Variants</b> <br>
Sun Solaris uses additional file types to store extended
file data, including ACLs and extended attributes, as
special entries in cpio archives.</p>

<p style="margin-left:6%; margin-top: 1em">XXX Others?

<p style="margin-top: 1em"><b>SEE ALSO</b></p>

<p style="margin-left:6%;">cpio(1), tar(5)</p>

<p style="margin-top: 1em"><b>STANDARDS</b></p>

<p style="margin-left:6%;">The <b>cpio</b> utility is no
longer a part of POSIX or the Single Unix Standard. It last
appeared in Version&nbsp;2 of the Single UNIX Specification
(&rsquo;&rsquo;SUSv2&rsquo;&rsquo;). It has been supplanted
in subsequent standards by pax(1). The portable ASCII format
is currently part of the specification for the pax(1)

<p style="margin-top: 1em"><b>HISTORY</b></p>

<p style="margin-left:6%;">The original cpio utility was
written by Dick Haight while working in AT&amp;T&rsquo;s
Unix Support Group. It appeared in 1977 as part of PWB/UNIX
1.0, the &rsquo;&rsquo;Programmer&rsquo;s Work
Bench&rsquo;&rsquo; derived from Version&nbsp;6 AT&amp;T
UNIX that was used internally at AT&amp;T. Both the old
binary and old character formats were in use by 1980,
according to the System III source released by SCO under
their &rsquo;&rsquo;Ancient Unix&rsquo;&rsquo; license. The
character format was adopted as part of IEEE Std 1003.1-1988
(&rsquo;&rsquo;POSIX.1&rsquo;&rsquo;). XXX when did
&quot;newc&quot; appear? Who invented it? When did HP come
out with their variant? When did Sun introduce ACLs and
extended attributes? XXX</p>

<p style="margin-top: 1em"><b>BUGS</b></p>

<p style="margin-left:6%;">The
&rsquo;&rsquo;CRC&rsquo;&rsquo; format is mis-named, as it
uses a simple checksum and not a cyclic redundancy

<p style="margin-left:6%; margin-top: 1em">The old binary
format is limited to 16 bits for user id, group id, device,
and inode numbers. It is limited to 4 gigabyte file

<p style="margin-left:6%; margin-top: 1em">The old ASCII
format is limited to 18 bits for the user id, group id,
device, and inode numbers. It is limited to 8 gigabyte file

<p style="margin-left:6%; margin-top: 1em">The new ASCII
format is limited to 4 gigabyte file sizes.</p>

<p style="margin-left:6%; margin-top: 1em">None of the cpio
formats store user or group names, which are essential when
moving files between systems with dissimilar user or group

<p style="margin-left:6%; margin-top: 1em">Especially when
writing older cpio variants, it may be necessary to map
actual device/inode values to synthesized values that fit
the available fields. With very large filesystems, this may
be necessary even for the newer formats.</p>

<p style="margin-left:6%; margin-top: 1em">BSD
December&nbsp;23, 2011 BSD</p>