245 lines
9.7 KiB
Groff
245 lines
9.7 KiB
Groff
.\" Copyright (c) 2003-2004 Tim Kientzle
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd April 27, 2004
|
|
.Dt libarchive-formats 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm libarchive-formats
|
|
.Nd archive formats supported by the libarchive library
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Xr libarchive 3
|
|
library reads and writes a variety of streaming archive formats.
|
|
Generally speaking, all of these archive formats consist of a series of
|
|
.Dq entries .
|
|
Each entry stores a single file system object, such as a file, directory,
|
|
or symbolic link.
|
|
.Pp
|
|
The following provides a brief description of each format supported
|
|
by libarchive, with some information about recognized extensions or
|
|
limitations of the current library support.
|
|
Note that just because a format is supported by libarchive does not
|
|
imply that a program that uses libarchive will support that format.
|
|
Applications that use libarchive specify which formats they wish
|
|
to support.
|
|
.Ss Tar Formats
|
|
The
|
|
.Xr libarchive 3
|
|
library can read most tar archives.
|
|
However, it only writes POSIX-standard
|
|
.Dq ustar
|
|
and
|
|
.Dq pax interchange
|
|
formats.
|
|
.Pp
|
|
All tar formats store each entry in one or more 512-byte records.
|
|
The first record is used for file metadata, including filename,
|
|
timestamp, and mode information, and the file data is stored in
|
|
subsequent records.
|
|
Later variants have extended this by either appropriating undefined
|
|
areas of the header record, extending the header to multiple records,
|
|
or by storing special entries that modify the interpretation of
|
|
subsequent entries.
|
|
.Pp
|
|
.Bl -tag -width indent
|
|
.It Cm gnutar
|
|
The
|
|
.Xr libarchive 3
|
|
library can read GNU-format tar archives.
|
|
It currently supports the most popular GNU extensions, including
|
|
modern long filename and linkname support, as well as atime and ctime data.
|
|
The libarchive library does not support sparse files, multi-volume
|
|
archives, nor the old GNU long filename format.
|
|
.It Cm pax
|
|
The
|
|
.Xr libarchive 3
|
|
library can read and write POSIX-compliant pax interchange format
|
|
archives.
|
|
Pax interchange format archives are an extension of the older ustar
|
|
format that adds a separate entry with additional attributes stored
|
|
as key/value pairs.
|
|
The presence of this additional entry is the only difference between
|
|
pax interchange format and the older ustar format.
|
|
The extended attributes are of unlimited length and are stored
|
|
as UTF-8 Unicode strings.
|
|
Keywords defined in the standard are in all lowercase; vendors are allowed
|
|
to define custom keys by preceding them with the vendor name in all uppercase.
|
|
When writing pax archives, libarchive uses many of the SCHILY keys
|
|
defined by Joerg Schilling's
|
|
.Dq star
|
|
archiver.
|
|
The libarchive library can read most of the SCHILY keys.
|
|
It ignores any keywords that it does not understand.
|
|
.It Cm restricted pax
|
|
The libarchive library can also write pax archives in which it
|
|
attempts to suppress the extended attributes entry whenever
|
|
possible.
|
|
The result will be identical to a ustar archive unless the
|
|
extended attributes entry is required to store a long file
|
|
name, long linkname, extended ACL, file flags, or if any of the standard
|
|
ustar data (user name, group name, UID, GID, etc) cannot be fully
|
|
represented in the ustar header.
|
|
In all cases, the result can be dearchived by any program that
|
|
can read POSIX-compliant pax interchange format archives.
|
|
.It Cm ustar
|
|
The libarchive library can both read and write this format.
|
|
This format has the following limitations:
|
|
.Bl -bullet -compact
|
|
.It
|
|
Device major and minor numbers are limited to 21 bits.
|
|
Nodes with larger numbers will not be added to the archive.
|
|
.It
|
|
Path names in the archive are limited to 255 bytes.
|
|
(Shorter if there is no / character in exactly the right place.)
|
|
.It
|
|
Symbolic links and hard links are stored in the archive with
|
|
the name of the referenced file.
|
|
This name is limited to 100 bytes.
|
|
.It
|
|
Extended attributes, file flags, and other extended
|
|
security information cannot be stored.
|
|
.It
|
|
Archive entries are limited to 2 gigabytes in size.
|
|
.El
|
|
Note that the pax interchange format has none of these restrictions.
|
|
.El
|
|
.Pp
|
|
The libarchive library can also read a variety of commonly-used extensions to
|
|
the basic tar format.
|
|
In particular, it supports base-256 values in certain numeric fields.
|
|
This essentially removes the limitations on file size, modification time,
|
|
and device numbers.
|
|
.Pp
|
|
The first tar program appeared in Sixth Edition Unix (circa 1976).
|
|
This makes the tar format one of the oldest and most widely-supported
|
|
archive formats.
|
|
The first official standard for the tar file format was the
|
|
.Dq ustar
|
|
(Unix Standard Tar) format defined by POSIX in 1988.
|
|
POSIX.1-2001 extended the ustar format to create the
|
|
.Dq pax interchange
|
|
format.
|
|
There have also been many custom variations.
|
|
.Ss Cpio Formats
|
|
The libarchive library can read a number of common cpio variants and can write
|
|
.Dq odc
|
|
format archives.
|
|
A cpio archive stores each entry as a fixed-size header followed
|
|
by a variable-length filename and variable-length data.
|
|
Unlike tar, cpio does only minimal padding of the header or file data.
|
|
There are a variety of cpio formats, which differ primarily in
|
|
how they store the initial header: some store the values as
|
|
octal or hexadecimal numbers in ASCII, others as binary values of
|
|
varying byte order and length.
|
|
.Bl -tag -width indent
|
|
.It Cm binary
|
|
The libarchive library can read both big-endian and little-endian
|
|
variants of the original binary cpio format.
|
|
This format used 32-bit binary values for file size and mtime,
|
|
and 16-bit binary values for the other fields.
|
|
.It Cm odc
|
|
The libarchive library can both read and write this
|
|
POSIX-standard format.
|
|
This format stores the header contents as octal values in ASCII.
|
|
It is standard, portable, and immune from byte-order confusion.
|
|
File sizes and mtime are limited to 33 bits (8GB file size),
|
|
other fields are limited to 18 bits.
|
|
.It Cm SVR4
|
|
The libarchive library can read both CRC and non-CRC variants of
|
|
this format.
|
|
The SVR4 format uses eight-digit hexadecimal values for
|
|
all header fields.
|
|
This limits file size to 4GB, and also limits the mtime and
|
|
other fields to 32 bits.
|
|
The SVR4 format can optionally include a CRC of the file
|
|
contents, although libarchive does not currently verify this CRC.
|
|
.El
|
|
.Pp
|
|
Cpio is an old format that was widely used because of its simplicity
|
|
and its support for very long filenames.
|
|
Unfortunately, it has many limitations that make it unsuitable
|
|
for widespread use.
|
|
Only the POSIX format permits files over 4GB, and its 18-bit
|
|
limit for most other fields makes it unsuitable for modern systems.
|
|
In addition, cpio formats only store numeric UID/GID values (not
|
|
usernames and group names), which can make it very difficult to correctly
|
|
transfer archives across systems.
|
|
Finally, there is no good way to extend the format, which means that
|
|
ACLs, file flags, character encoding information, and non-standard file
|
|
types can not be added except by breaking compatibility with existing
|
|
implementations.
|
|
.Ss Shar Formats
|
|
A
|
|
.Dq shell archive
|
|
is a shell script that, when executed on a POSIX-compliant
|
|
system, will recreate a collection of file system objects.
|
|
The libarchive library can write two different kinds of shar archives:
|
|
.Bl -tag -width indent
|
|
.It Cm shar
|
|
The traditional shar format uses a limited set of POSIX
|
|
commands, including
|
|
.Xr echo 1 ,
|
|
.Xr mkdir 1 ,
|
|
and
|
|
.Xr sed 1 .
|
|
It is suitable for portably archiving small collections of plain text files.
|
|
However, it is not generally well-suited for large archives
|
|
(many implementations of
|
|
.Xr sh 1
|
|
have limits on the size of a script) nor should it be used with non-text files.
|
|
.It Cm shardump
|
|
This format is similar to shar but encodes files using
|
|
.Xr uuencode 1
|
|
so that the result will be a plain text file regardless of the file contents.
|
|
It also includes additional shell commands that attempt to reproduce as
|
|
many file attributes as possible, including owner, mode, and flags.
|
|
The additional commands used to restore file attributes make
|
|
shardump archives less portable than plain shar archives.
|
|
.El
|
|
.Ss ISO9660 format
|
|
Libarchive can read and extract from files containing ISO9660-compliant
|
|
CDROM images.
|
|
It also has partial support for Rockridge extensions.
|
|
In many cases, this can remove the need to burn a physical CDROM.
|
|
It also avoids security and complexity issues that come with
|
|
virtual mounts and loopback devices.
|
|
.Ss Zip format
|
|
Libarchive can extract from most zip format archives.
|
|
It currently only supports uncompressed entries and entries
|
|
compressed with the
|
|
.Dq deflate
|
|
algorithm.
|
|
Older zip compression algorithms are not supported.
|
|
.Sh SEE ALSO
|
|
.Xr cpio 1 ,
|
|
.Xr mkisofs 1 ,
|
|
.Xr shar 1 ,
|
|
.Xr tar 1 ,
|
|
.Xr zip 1 ,
|
|
.Xr zlib 3 ,
|
|
.Xr tar 5
|