1# Welcome to libarchive! 2 3The libarchive project develops a portable, efficient C library that 4can read and write streaming archives in a variety of formats. It 5also includes implementations of the common `tar`, `cpio`, and `zcat` 6command-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 20This 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 30The 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 39The 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 45In addition to the informational articles and documentation 46in the online [libarchive Wiki](https://github.com/libarchive/libarchive/wiki), 47the 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 64The manual pages above are provided in the 'doc' directory in 65a number of different formats. 66 67You should also read the copious comments in `archive.h` and the 68source code for the sample programs for more details. Please let us 69know about any errors or omissions you find. 70 71## Supported Formats 72 73Currently, the library automatically detects and reads the following fomats: 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 * ISO9660 CD-ROM images (with optional Rockridge or Joliet extensions) 83 * ZIP archives (with uncompressed or "deflate" compressed entries, including support for encrypted Zip archives) 84 * ZIPX archives (with support for bzip2, ppmd8, lzma and xz compressed entries) 85 * GNU and BSD 'ar' archives 86 * 'mtree' format 87 * 7-Zip archives 88 * Microsoft CAB format 89 * LHA and LZH archives 90 * RAR and RAR 5.0 archives (with some limitations due to RAR's proprietary status) 91 * XAR archives 92 93The library also detects and handles any of the following before evaluating the archive: 94 * uuencoded files 95 * files with RPM wrapper 96 * gzip compression 97 * bzip2 compression 98 * compress/LZW compression 99 * lzma, lzip, and xz compression 100 * lz4 compression 101 * lzop compression 102 * zstandard compression 103 104The library can create archives in any of the following formats: 105 * POSIX ustar 106 * POSIX pax interchange format 107 * "restricted" pax format, which will create ustar archives except for 108 entries that require pax extensions (for long filenames, ACLs, etc). 109 * Old GNU tar format 110 * Old V7 tar format 111 * POSIX octet-oriented cpio 112 * SVR4 "newc" cpio 113 * shar archives 114 * ZIP archives (with uncompressed or "deflate" compressed entries) 115 * GNU and BSD 'ar' archives 116 * 'mtree' format 117 * ISO9660 format 118 * 7-Zip archives 119 * XAR archives 120 121When creating archives, the result can be filtered with any of the following: 122 * uuencode 123 * gzip compression 124 * bzip2 compression 125 * compress/LZW compression 126 * lzma, lzip, and xz compression 127 * lz4 compression 128 * lzop compression 129 * zstandard compression 130 131## Notes about the Library Design 132 133The following notes address many of the most common 134questions we are asked about libarchive: 135 136* This is a heavily stream-oriented system. That means that 137 it is optimized to read or write the archive in a single 138 pass from beginning to end. For example, this allows 139 libarchive to process archives too large to store on disk 140 by processing them on-the-fly as they are read from or 141 written to a network or tape drive. This also makes 142 libarchive useful for tools that need to produce 143 archives on-the-fly (such as webservers that provide 144 archived contents of a users account). 145 146* In-place modification and random access to the contents 147 of an archive are not directly supported. For some formats, 148 this is not an issue: For example, tar.gz archives are not 149 designed for random access. In some other cases, libarchive 150 can re-open an archive and scan it from the beginning quickly 151 enough to provide the needed abilities even without true 152 random access. Of course, some applications do require true 153 random access; those applications should consider alternatives 154 to libarchive. 155 156* The library is designed to be extended with new compression and 157 archive formats. The only requirement is that the format be 158 readable or writable as a stream and that each archive entry be 159 independent. There are articles on the libarchive Wiki explaining 160 how to extend libarchive. 161 162* On read, compression and format are always detected automatically. 163 164* The same API is used for all formats; it should be very 165 easy for software using libarchive to transparently handle 166 any of libarchive's archiving formats. 167 168* Libarchive's automatic support for decompression can be used 169 without archiving by explicitly selecting the "raw" and "empty" 170 formats. 171 172* I've attempted to minimize static link pollution. If you don't 173 explicitly invoke a particular feature (such as support for a 174 particular compression or format), it won't get pulled in to 175 statically-linked programs. In particular, if you don't explicitly 176 enable a particular compression or decompression support, you won't 177 need to link against the corresponding compression or decompression 178 libraries. This also reduces the size of statically-linked 179 binaries in environments where that matters. 180 181* The library is generally _thread safe_ depending on the platform: 182 it does not define any global variables of its own. However, some 183 platforms do not provide fully thread-safe versions of key C library 184 functions. On those platforms, libarchive will use the non-thread-safe 185 functions. Patches to improve this are of great interest to us. 186 187* In particular, libarchive's modules to read or write a directory 188 tree do use `chdir()` to optimize the directory traversals. This 189 can cause problems for programs that expect to do disk access from 190 multiple threads. Of course, those modules are completely 191 optional and you can use the rest of libarchive without them. 192 193* The library is _not_ thread aware, however. It does no locking 194 or thread management of any kind. If you create a libarchive 195 object and need to access it from multiple threads, you will 196 need to provide your own locking. 197 198* On read, the library accepts whatever blocks you hand it. 199 Your read callback is free to pass the library a byte at a time 200 or mmap the entire archive and give it to the library at once. 201 On write, the library always produces correctly-blocked output. 202 203* The object-style approach allows you to have multiple archive streams 204 open at once. bsdtar uses this in its "@archive" extension. 205 206* The archive itself is read/written using callback functions. 207 You can read an archive directly from an in-memory buffer or 208 write it to a socket, if you wish. There are some utility 209 functions to provide easy-to-use "open file," etc, capabilities. 210 211* The read/write APIs are designed to allow individual entries 212 to be read or written to any data source: You can create 213 a block of data in memory and add it to a tar archive without 214 first writing a temporary file. You can also read an entry from 215 an archive and write the data directly to a socket. If you want 216 to read/write entries to disk, there are convenience functions to 217 make this especially easy. 218 219* Note: The "pax interchange format" is a POSIX standard extended tar 220 format that should be used when the older _ustar_ format is not 221 appropriate. It has many advantages over other tar formats 222 (including the legacy GNU tar format) and is widely supported by 223 current tar implementations. 224 225