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 * POSIX octet-oriented cpio 82 * Binary cpio (big-endian or little-endian) 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 * GNU and BSD 'ar' archives 86 * 'mtree' format 87 * 7-Zip archives 88 * Microsoft CAB format 89 * LHA and LZH archives 90 * RAR 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 103The library can create archives in any of the following formats: 104 * POSIX ustar 105 * POSIX pax interchange format 106 * "restricted" pax format, which will create ustar archives except for 107 entries that require pax extensions (for long filenames, ACLs, etc). 108 * Old GNU tar format 109 * Old V7 tar format 110 * POSIX octet-oriented cpio 111 * SVR4 "newc" cpio 112 * shar archives 113 * ZIP archives (with uncompressed or "deflate" compressed entries) 114 * GNU and BSD 'ar' archives 115 * 'mtree' format 116 * ISO9660 format 117 * 7-Zip archives 118 * XAR archives 119 120When creating archives, the result can be filtered with any of the following: 121 * uuencode 122 * gzip compression 123 * bzip2 compression 124 * compress/LZW compression 125 * lzma, lzip, and xz compression 126 * lz4 compression 127 * lzop compression 128 129## Notes about the Library Design 130 131The following notes address many of the most common 132questions we are asked about libarchive: 133 134* This is a heavily stream-oriented system. That means that 135 it is optimized to read or write the archive in a single 136 pass from beginning to end. For example, this allows 137 libarchive to process archives too large to store on disk 138 by processing them on-the-fly as they are read from or 139 written to a network or tape drive. This also makes 140 libarchive useful for tools that need to produce 141 archives on-the-fly (such as webservers that provide 142 archived contents of a users account). 143 144* In-place modification and random access to the contents 145 of an archive are not directly supported. For some formats, 146 this is not an issue: For example, tar.gz archives are not 147 designed for random access. In some other cases, libarchive 148 can re-open an archive and scan it from the beginning quickly 149 enough to provide the needed abilities even without true 150 random access. Of course, some applications do require true 151 random access; those applications should consider alternatives 152 to libarchive. 153 154* The library is designed to be extended with new compression and 155 archive formats. The only requirement is that the format be 156 readable or writable as a stream and that each archive entry be 157 independent. There are articles on the libarchive Wiki explaining 158 how to extend libarchive. 159 160* On read, compression and format are always detected automatically. 161 162* The same API is used for all formats; in particular, it's very 163 easy for software using libarchive to transparently handle 164 any of libarchive's archiving formats. 165 166* Libarchive's automatic support for decompression can be used 167 without archiving by explicitly selecting the "raw" and "empty" 168 formats. 169 170* I've attempted to minimize static link pollution. If you don't 171 explicitly invoke a particular feature (such as support for a 172 particular compression or format), it won't get pulled in to 173 statically-linked programs. In particular, if you don't explicitly 174 enable a particular compression or decompression support, you won't 175 need to link against the corresponding compression or decompression 176 libraries. This also reduces the size of statically-linked 177 binaries in environments where that matters. 178 179* The library is generally _thread safe_ depending on the platform: 180 it does not define any global variables of its own. However, some 181 platforms do not provide fully thread-safe versions of key C library 182 functions. On those platforms, libarchive will use the non-thread-safe 183 functions. Patches to improve this are of great interest to us. 184 185* In particular, libarchive's modules to read or write a directory 186 tree do use `chdir()` to optimize the directory traversals. This 187 can cause problems for programs that expect to do disk access from 188 multiple threads. Of course, those modules are completely 189 optional and you can use the rest of libarchive without them. 190 191* The library is _not_ thread aware, however. It does no locking 192 or thread management of any kind. If you create a libarchive 193 object and need to access it from multiple threads, you will 194 need to provide your own locking. 195 196* On read, the library accepts whatever blocks you hand it. 197 Your read callback is free to pass the library a byte at a time 198 or mmap the entire archive and give it to the library at once. 199 On write, the library always produces correctly-blocked output. 200 201* The object-style approach allows you to have multiple archive streams 202 open at once. bsdtar uses this in its "@archive" extension. 203 204* The archive itself is read/written using callback functions. 205 You can read an archive directly from an in-memory buffer or 206 write it to a socket, if you wish. There are some utility 207 functions to provide easy-to-use "open file," etc, capabilities. 208 209* The read/write APIs are designed to allow individual entries 210 to be read or written to any data source: You can create 211 a block of data in memory and add it to a tar archive without 212 first writing a temporary file. You can also read an entry from 213 an archive and write the data directly to a socket. If you want 214 to read/write entries to disk, there are convenience functions to 215 make this especially easy. 216 217* Note: The "pax interchange format" is a POSIX standard extended tar 218 format that should be used when the older _ustar_ format is not 219 appropriate. It has many advantages over other tar formats 220 (including the legacy GNU tar format) and is widely supported by 221 current tar implementations. 222 223