README.md

   1 # Welcome to libarchive!
   2
   3 The libarchive project develops a portable, efficient C library that
   4 can read and write streaming archives in a variety of formats.  It
   5 also includes implementations of the common `tar`, `cpio`, and `zcat`
   6 command-line tools that use the libarchive library.
   7
   8 ## Questions?  Issues?
   9
  10 * http://www.libarchive.org is the home for ongoing
  11   libarchive development, including documentation,
  12   and links to the libarchive mailing lists.
  13 * To report an issue, use the issue tracker at
  14   https://github.com/libarchive/libarchive/issues
  15 * To submit an enhancement to libarchive, please
  16   submit a pull request via GitHub: https://github.com/libarchive/libarchive/pulls
  17
  18 ## Contents of the Distribution
  19
  20 This distribution bundle includes the following major components:
  21
  22 * **libarchive**: a library for reading and writing streaming archives
  23 * **tar**: the 'bsdtar' program is a full-featured 'tar' implementation built on libarchive
  24 * **cpio**: the 'bsdcpio' program is a different interface to essentially the same functionality
  25 * **cat**: the 'bsdcat' program is a simple replacement tool for zcat, bzcat, xzcat, and such
  26 * **examples**: Some small example programs that you may find useful.
  27 * **examples/minitar**: a compact sample demonstrating use of libarchive.
  28 * **contrib**:  Various items sent to me by third parties; please contact the authors with any questions.
  29
  30 The top-level directory contains the following information files:
  31
  32 * **NEWS** - highlights of recent changes
  33 * **COPYING** - what you can do with this
  34 * **INSTALL** - installation instructions
  35 * **README** - this file
  36 * **CMakeLists.txt** - input for "cmake" build tool, see INSTALL
  37 * **configure** - configuration script, see INSTALL for details.  If your copy of the source lacks a `configure` script, you can try to construct it by running the script in `build/autogen.sh` (or use `cmake`).
  38
  39 The following files in the top-level directory are used by the 'configure' script:
  40 * `Makefile.am`, `aclocal.m4`, `configure.ac` - used to build this distribution, only needed by maintainers
  41 * `Makefile.in`, `config.h.in` - templates used by configure script
  42
  43 ## Documentation
  44
  45 In addition to the informational articles and documentation
  46 in the online [libarchive Wiki](https://github.com/libarchive/libarchive/wiki),
  47 the distribution also includes a number of manual pages:
  48
  49  * bsdtar.1 explains the use of the bsdtar program
  50  * bsdcpio.1 explains the use of the bsdcpio program
  51  * bsdcat.1 explains the use of the bsdcat program
  52  * libarchive.3 gives an overview of the library as a whole
  53  * archive_read.3, archive_write.3, archive_write_disk.3, and
  54    archive_read_disk.3 provide detailed calling sequences for the read
  55    and write APIs
  56  * archive_entry.3 details the "struct archive_entry" utility class
  57  * archive_internals.3 provides some insight into libarchive's
  58    internal structure and operation.
  59  * libarchive-formats.5 documents the file formats supported by the library
  60  * cpio.5, mtree.5, and tar.5 provide detailed information about these
  61    popular archive formats, including hard-to-find details about
  62    modern cpio and tar variants.
  63
  64 The manual pages above are provided in the 'doc' directory in
  65 a number of different formats.
  66
  67 You should also read the copious comments in `archive.h` and the
  68 source code for the sample programs for more details.  Please let us
  69 know about any errors or omissions you find.
  70
  71 ## Supported Formats
  72
  73 Currently, the library automatically detects and reads the following formats:
  74   * Old V7 tar archives
  75   * POSIX ustar
  76   * GNU tar format (including GNU long filenames, long link names, and sparse files)
  77   * Solaris 9 extended tar format (including ACLs)
  78   * POSIX pax interchange format
  79   * POSIX octet-oriented cpio
  80   * SVR4 ASCII cpio
  81   * Binary cpio (big-endian or little-endian)
  82   * PWB binary cpio
  83   * ISO9660 CD-ROM images (with optional Rockridge or Joliet extensions)
  84   * ZIP archives (with uncompressed or "deflate" compressed entries, including support for encrypted Zip archives)
  85   * ZIPX archives (with support for bzip2, ppmd8, lzma and xz compressed entries)
  86   * GNU and BSD 'ar' archives
  87   * 'mtree' format
  88   * 7-Zip archives
  89   * Microsoft CAB format
  90   * LHA and LZH archives
  91   * RAR and RAR 5.0 archives (with some limitations due to RAR's proprietary status)
  92   * XAR archives
  93
  94 The library also detects and handles any of the following before evaluating the archive:
  95   * uuencoded files
  96   * files with RPM wrapper
  97   * gzip compression
  98   * bzip2 compression
  99   * compress/LZW compression
 100   * lzma, lzip, and xz compression
 101   * lz4 compression
 102   * lzop compression
 103   * zstandard compression
 104
 105 The library can create archives in any of the following formats:
 106   * POSIX ustar
 107   * POSIX pax interchange format
 108   * "restricted" pax format, which will create ustar archives except for
 109     entries that require pax extensions (for long filenames, ACLs, etc).
 110   * Old GNU tar format
 111   * Old V7 tar format
 112   * POSIX octet-oriented cpio
 113   * SVR4 "newc" cpio
 114   * Binary cpio (little-endian)
 115   * PWB binary cpio
 116   * shar archives
 117   * ZIP archives (with uncompressed or "deflate" compressed entries)
 118   * GNU and BSD 'ar' archives
 119   * 'mtree' format
 120   * ISO9660 format
 121   * 7-Zip archives
 122   * XAR archives
 123
 124 When creating archives, the result can be filtered with any of the following:
 125   * uuencode
 126   * gzip compression
 127   * bzip2 compression
 128   * compress/LZW compression
 129   * lzma, lzip, and xz compression
 130   * lz4 compression
 131   * lzop compression
 132   * zstandard compression
 133
 134 ## Notes about the Library Design
 135
 136 The following notes address many of the most common
 137 questions we are asked about libarchive:
 138
 139 * This is a heavily stream-oriented system.  That means that
 140   it is optimized to read or write the archive in a single
 141   pass from beginning to end.  For example, this allows
 142   libarchive to process archives too large to store on disk
 143   by processing them on-the-fly as they are read from or
 144   written to a network or tape drive.  This also makes
 145   libarchive useful for tools that need to produce
 146   archives on-the-fly (such as webservers that provide
 147   archived contents of a users account).
 148
 149 * In-place modification and random access to the contents
 150   of an archive are not directly supported.  For some formats,
 151   this is not an issue: For example, tar.gz archives are not
 152   designed for random access.  In some other cases, libarchive
 153   can re-open an archive and scan it from the beginning quickly
 154   enough to provide the needed abilities even without true
 155   random access.  Of course, some applications do require true
 156   random access; those applications should consider alternatives
 157   to libarchive.
 158
 159 * The library is designed to be extended with new compression and
 160   archive formats.  The only requirement is that the format be
 161   readable or writable as a stream and that each archive entry be
 162   independent.  There are articles on the libarchive Wiki explaining
 163   how to extend libarchive.
 164
 165 * On read, compression and format are always detected automatically.
 166
 167 * The same API is used for all formats; it should be very
 168   easy for software using libarchive to transparently handle
 169   any of libarchive's archiving formats.
 170
 171 * Libarchive's automatic support for decompression can be used
 172   without archiving by explicitly selecting the "raw" and "empty"
 173   formats.
 174
 175 * I've attempted to minimize static link pollution.  If you don't
 176   explicitly invoke a particular feature (such as support for a
 177   particular compression or format), it won't get pulled in to
 178   statically-linked programs.  In particular, if you don't explicitly
 179   enable a particular compression or decompression support, you won't
 180   need to link against the corresponding compression or decompression
 181   libraries.  This also reduces the size of statically-linked
 182   binaries in environments where that matters.
 183
 184 * The library is generally _thread safe_ depending on the platform:
 185   it does not define any global variables of its own.  However, some
 186   platforms do not provide fully thread-safe versions of key C library
 187   functions.  On those platforms, libarchive will use the non-thread-safe
 188   functions.  Patches to improve this are of great interest to us.
 189
 190 * In particular, libarchive's modules to read or write a directory
 191   tree do use `chdir()` to optimize the directory traversals.  This
 192   can cause problems for programs that expect to do disk access from
 193   multiple threads.  Of course, those modules are completely
 194   optional and you can use the rest of libarchive without them.
 195
 196 * The library is _not_ thread aware, however.  It does no locking
 197   or thread management of any kind.  If you create a libarchive
 198   object and need to access it from multiple threads, you will
 199   need to provide your own locking.
 200
 201 * On read, the library accepts whatever blocks you hand it.
 202   Your read callback is free to pass the library a byte at a time
 203   or mmap the entire archive and give it to the library at once.
 204   On write, the library always produces correctly-blocked output.
 205
 206 * The object-style approach allows you to have multiple archive streams
 207   open at once.  bsdtar uses this in its "@archive" extension.
 208
 209 * The archive itself is read/written using callback functions.
 210   You can read an archive directly from an in-memory buffer or
 211   write it to a socket, if you wish.  There are some utility
 212   functions to provide easy-to-use "open file," etc, capabilities.
 213
 214 * The read/write APIs are designed to allow individual entries
 215   to be read or written to any data source:  You can create
 216   a block of data in memory and add it to a tar archive without
 217   first writing a temporary file.  You can also read an entry from
 218   an archive and write the data directly to a socket.  If you want
 219   to read/write entries to disk, there are convenience functions to
 220   make this especially easy.
 221
 222 * Note: The "pax interchange format" is a POSIX standard extended tar
 223   format that should be used when the older _ustar_ format is not
 224   appropriate.  It has many advantages over other tar formats
 225   (including the legacy GNU tar format) and is widely supported by
 226   current tar implementations.
 227